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The effect of falling height on muscle activity and foot motion during landings
Journal of Electromyography and Kinesiology 13 (2003) 533–544 www.elsevier.com/locate/jelekin
The effect of falling height on muscle activity and foot motion during landings Adamantios Arampatzis ∗, Gaspar Morey-Klapsing, Gert-Peter Bru¨ggemann Institute for Biomechanics, German Sport University of Cologne, Carl-Diem-Weg 6, 50933 Cologne, Germany Received 10 July 2002; received in revised form 24 April 2003; accepted 1 May 2003
Abstract The aims of this study were: (a) to examine the effect of falling height on the kinematics of the tibiotalar, talonavicular and calcaneocuboid joints and (b) to study the influence of falling height on the muscle activity of the leg during landings. Six female gymnasts (height: 1.63 ± 0.04 m, weight: 58.21 ± 3.46 kg) participated in this study. All six gymnasts carried out barefoot landings, falling from 1.0, 1.5 and 2.0 m height onto a mat. Three genlocked digital high speed video cameras (250 Hz) captured the motion of the left shank and foot. Surface electromyography (EMG) was used to measure muscle activity (1000 Hz) from five muscles (gastrocnemius medialis, tibialis anterior, peroneus longus, vastus lateralis and hamstrings) of the left leg. The kinematics of the tibiotalar, talonavicular and calcaneocuboid joints were studied. The lower-leg and the foot were modelled by means of a multibody system, comprising seven rigid bodies. The falling height does not show any influence on the kinematics neither of the tibiotalar nor of the talonavicular joints during landing. The eversion at the calcaneocuboid joint increases with increasing falling height. When augmenting falling height, the myoelectric activity of the muscles of the lower limb increases as well during the preactivation phase as during the landing itself. The muscles of the lower extremities are capable of stabilizing the tibiotalar and the talonavicular joints actively, restricting their maximal motion by means of a higher activation before and after touchdown. Maximal eversion at the calcaneocuboid joint increases about 52% when landing from 2.0 m. 2003 Elsevier Ltd. All rights reserved. Keywords: Modelling; Rearfoot kinematics; Forefoot kinematics; Eversion; Tibial rotation; Foot stability; Mat deformation; EMG-activity
1. Introduction In the literature it is reported that, an excessive eversion at the ankle joint and an excessive internal rotation of the tibia during running may lead to overload and injury at the foot and the knee [1,2]. As an example, an excessive eversion has been associated to Achilles tendon diseases and an excessive tibial rotation has been associated to patellofemoral pain syndrome [3,4]. It has also been suggested that eversion of the ankle joint may be induced by ground reaction forces [5] and that higher ground reaction forces can alter this eversion [4]. In gymnastic landings, the ground reaction forces reach values above 10 times bodyweight [6] which may lead to an overload of the lower extremities. On the other hand, muscle activity and enhanced muscle strength are
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1050-6411/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1050-6411(03)00059-2
able to reduce the eversion at the ankle joint, protecting it from excessive motion [7,8]. Falling height has an effect on ground reaction forces [9,10] and on the myoelectric activity of the muscles of the lower limb [9]. All these observations point towards the potential influence that falling height might have on ankle joint motion, leading to excessive joint excursions. They also show that the muscles of the lower limb exhibit a higher myoelectric activity which in turn may result in a higher joint stability. Therefore it can be hypothesized that the muscles, by means of a higher activation, could be able to restrict the excessive eversion of the ankle joint and the excessive tibia-rotation induced by an increased falling height. Whether or not changes in eversion of the ankle joint or in tibia rotation are induced by falling height has not yet been studied. Furthermore, recent studies [3] mention that midfoot and forefoot kinematics may be more important than those of the calcaneus for understanding orthotic effects. The motion of the midfoot or the forefoot during landings have not yet been
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studied either. Therefore the aims of this study were: (a) to examine the effect of falling height on the kinematics of the tibiotalar, talonavicular and calcaneocuboid joints using a shank–foot model and (b) to study the influence of falling height on the activity of leg muscles during landings.
3. Tuberositas naviculare (most medial point) 4. Os Cuboideum (diagonal superior to the basis of the fifth metatarsal) 5. Malleolus medialis (most medial point) 6. Malleolus lateralis (most lateral point) 7. Condilus medialis tibiae (most medial point) 8. Caput fibula (most lateral point)
2. Methods
Other markers
2.1. Experimental protocol
9. Caput metatarsale I (medial superior) 10. Caput metatarsale V (lateral superior) 11. Caput metatarsale II-III (between second and third metatarsal heads) 12. Metatarsus I (more proximal) 13. Metatarsus V (more proximal) 14. Os naviculare (on the instep) 15. Calcaneus medial (more anterior) 16. Calcaneus medial (more posterior) 17. Calcaneus lateral 18. Fascies tibiae
Six female gymnasts (height: 1.63 ± 0.04 m, weight: 58.21 ± 3.46 kg), active members of the university gymnastics team, participated in this study. The six gymnasts performed barefoot landings falling from 1.0, 1.5 and 2.0 m height onto a mat. The order of the falling heights was systematically changed among subjects. The first and the fourth gymnasts started the experiment with 1.0 m height and then continued with the 1.5 and 2.0 m heights. The second and the fifth gymnasts started with the 1.5 m height and finally the third and the sixth gymnasts started with the 2.0 m height. The size of the mat was 200 × 200 × 30 cm3. The mechanical properties of the mat (stiffness and damping) was similar to those used in gymnastic training and competition. Three genlocked digital high speed video cameras (250 Hz) captured the motion of the left shank and foot. Eighteen reflective markers were attached to the left shank and foot (Fig. 1). Eight markers were fixed on pre-defined anatomical landmarks to allow the definition of the joint coordinate systems. The remaining markers were placed on not strictly defined anatomical positions but rather on locations were lesser skin movements were expected. Below is a list of the marker locations: Bony landmarks 1. Caput metatarsale I (most medial point) 2. Caput metatarsale V (most lateral point)
Fig. 1.
The video sequences were digitised using the automatic tracking option from the “Peak Motus” system. When marker reflection was not good enough for automatic tracking, those points were digitised manually. Those trials where a marker was hidden (for example by arm movement), were excluded from the analysis. All three cameras covered a volume of approximately 60 x 60 x 60 cm3. A 30 x 30 x 30 cm3 cube was used to calibrate the cameras. To estimate the accuracy of the measurement 11 points from the calibration frame having known coordinates were digitised. These points were different to those used for calibration. All points were manually digitised and their coordinates calculated for 14 different calibrations. The absolute differences between real and measured coordinates ranged from 0.59 ± 0.06 to 2.06 ± 0.20 mm. A former estimation of the accuracy was done by considering the distance
Medial, front and lateral view of the marker placement used to define the shank–foot model
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between both malleolar markers during landing. This was compared to the same distance as calculated from the reference sequence. The malleoli were chosen because almost no deformation and therefore no change in the distance between them is expected. The absolute observed change was ±3 mm. Bipolar EMG leadoffs, with pre-amplification (bandwidth 10–500 Hz), were used to record muscle activity. Adhesive surface electrodes (Ag/AgCl) with an electrolytic gel interface and a pickup surface of 0.8 cm2 (blue sensor-Medicotest Denmark) were positioned above the midpoint of the muscle belly. The inter-electrode distance was 2 cm and electrodes were placed parallel to the presumed direction of the muscle fibers. The electrodes were further secured to the skin with elastic tape together with the pre-amplifier to reduce motion artefacts. The skin was carefully prepared (shaved and cleaned with alcohol) to reduce skin impedance. The studied muscles were: gastrocnemius medialis (GM), tibialis anterior (TA), peroneus longus (PL), vastus lateralis (VL) and hamstrings (HA). Muscles were identified by palpation. The EMG signal was recorded at 1000 Hz sampling frequency. Before the experiment started, the EMG signal for each muscle was checked online for artefacts due to mechanical causes by passively shaking the leg. Additionally, several tests of muscle activity were undertaken to determine whether a good signal was obtained from each muscle. The test included isometric contractions for each muscle group and one and two legged hopping. The preparation was renewed when such artefacts were observed. All landings were performed within one testing period, and no electrode replacement was necessary during the measurements. The synchronization of the kinematic and EMG data was done by starting the measurement systems with a common trigger. 2.2. Reference measurement Foot motion was determined with reference to a neutral position (Fig. 1). To define the neutral position, the left foot and shank from each subject were placed in an inertial reference coordinate system (RCS). The RCS had axis 1 pointing forward, axis 2 in mediolateral direction and axis 3 being vertical pointing towards the ground. The plane defined by axis 1 and 2 was parallel to the ground. The neutral position of the shank and foot was defined as follows: the shank was vertical (tip of the lateral malleolus directly below the tip of the caput fibula with no lateral inclination) corresponding to the direction of the third axis of the RCS. The foot was flat on the ground, its longitudinal axis (Tuberositas calcanei–Caput metatarsale III) parallel to the first axis of the RCS and the medial aspect of the foot pointing in direction of axis 2 from the RCS. All 18 markers were filmed in this neutral position using 3 cameras (50 Hz) to calculate their 3D coordinates.
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2.3. The shank–foot model The lower-leg and the foot were modelled by means of a multi-body system, comprising seven rigid bodies (Fig. 2). The software used for modelling purposes was the simulation software “alaska” (advanced lagrangian solver in kinetic analysis, version 3.0, Chemnitz, [11]). For the elaboration of the model special attention was given to the functional anatomy of the foot [12]. The definition of the model is represented in Table 1. The talocalcaneal and the two metatarsophalangeal joints were not used in the present study. We did not consider the talocalcaneal joint, because it is very difficult to identify adequate points on the talus. The following constraints were imposed for the whole motion process: No motion at the three last cited joints was allowed. Due to the simplifications done in the model, the tibiotalar joint included the motion of both, the tibiotalar and the talocalcaneal joints. The talonavicular joint represents the motion occurring between the medial forefoot and the rearfoot and in the same fashion the calcaneocuboid joint represents the motion between the lateral forefoot and the rearfoot. This should clarify that, the reported data were calculated by means of a model and do not exactly represent the motion of the bones of the foot. However, to our belief, the model allows to examine the effect of different falling heights on forefoot and rearfoot motion during landings. For each joint, two joint coordinate systems (JCS) attached to each of the connected segments were defined. The JCS were defined in the neutral position using the above-mentioned bony landmarks (markers 1 to 8). The definition of each JCS is described below: 2.3.1. Tibiotalar joint (TTJ) JCS1: Origin was set at the midpoint of the line joining both malleoli. Axis 3 is defined by the line joining
Fig. 2.
Shank–foot model
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Table 1 Definition of the segments and joints of the shank–foot model Segments
Bones
Joints
Connected segments
Degree of freedom
Segment Segment Segment Segment
Tibia and fibula Talus Calcaneus Os naviculare, three cuneiformi, and metatarsals I,II,III Cuboid and metatarsals IV,V Phalanges I,II,III Phalanges IV,V
Free joint Tibiotalar joint Talocalcaneal joint Talonavicular joint
Space–segment1 Segment1–segment2 Segment2–segment3 Segment2–segment4
6 3 1 3
Calcaneocuboid joint Metatarsophalan-geal joint 1 Metatarsophalan-geal joint 2
Segment3–segment5 Segment4–segment6 Segment5–segment7
3 (ball-socket joint) 1 (rotational joint) 1 (rotational joint)
1 2 3 4
Segment5 Segment 6 Segment 7
the origin with the midpoint between landmarks 7 and 8. Axis 3 points downwards. Axis 2 is orthogonal to axis 3 and contained in the plane defined by axis 3 and the line joining the malleoli. Axis 2 points towards medial. Axis 1 results from the cross product of axes 3 and 2. JCS2: Results from moving the RCS to the origin as defined for JCS1. 2.3.2. Talonavicular joint (TNJ) JCS1: Results from moving the RCS to the origin, which is located at the level of landmark 3, at the midpoint of the 3/5 of the mediolateral distance between Tuberositas naviculare and Os cuboideum. JCS2: Same origin as JCS1. Axis 2 corresponds to axis 2 of the RCS transported to the origin. Axis 1 is orthogonal to axis 2 and contained in the plane defined by axis 2 and the line joining landmarks 1 and 3. Axis 3 results from the cross product of axes 1 and 2. 2.3.3. Calcaneocuboid joint (CCJ) JCS1: Results from moving the RCS to the origin which is located at the level of the Os cuboideum, at the midpoint of the 2/5 of the mediolateral distance between Os cuboideum and tuberositas naviculare. JCS2: Same origin as JCS1. Axis 2 corresponds to axis 2 of the RCS transported to the origin. Axis 1 is orthogonal to axis 2 and contained in the plane defined by axis 2 and the line joining landmarks 2 and 4. Axis 3 results from the cross product of axes 1 and 2. Markers 9–18 were fixed onto the segments of the model, using their 3D coordinates from the reference measurement in neutral position. These markers (9–18) plus both malleoli were used for the dynamic tracking. The remaining six markers were detached before performing the landings. The 12 markers kept were tracked in space during the analysis of the landings. Their 3D coordinates allowed the calculation of the model motion and hence, the motion at the tibiotalar, calcaneonavicular and calcaneocuboid joints as defined above. Segment 1 contains markers 5, 6 and 18, segment 2 markers 15, 16 and 17, segment 3 markers 9, 12 and 14 and segment 4 markers 10, 11 and 13. In an attempt to account for the relative motion of the markers caused by soft tissue
(free joint) (ball-socket joint) (rotational joint) (ball-socket joint)
movements and deformation, the markers were attached to the model using 3D linear spring damping elements. This method does not harm the constraints of the model. From 106 N/m on, the spring constant chosen for the tracking gives back stable coordinates without oscillation. Based on experience, the damping was set a hundredfold lower. For this application the spring constant was set to k = 106 N / m and the damping constant was set to b = 104 N s / m. 2.4. Data analysis The kinematics of the tibiotalar, talonavicular and calcaneocuboid joints, were defined by the orientation of the second bone coordinate system with respect to the first one. Eversion–inversion, dorsi–plantar flexion and adduction–abduction are defined by the bryant angles (α,β,γ) as follows: α (eversion–inversion): Angle between the second axis of JCS1 (‘2’JCS1) and the nodal line ‘3’JCS2 × ‘1’JCS1. a ⬎ 0, when (‘2’JCS1, ‘3’JCS2 × ‘1’JCS1, ‘1’JCS1) form a right handed system. This motion corresponds to a rotation about the first axis of JCS1 (‘1’JCS1). This rotation transfers JCS1 in JCS1,2. β (dorsal–plantar flexion): Angle between ‘3’JCS1 and ‘3’JCS2 b ⬎ 0 when (‘3’JCS1,2, ‘3’JCS2, ‘2’JCS1,2) form a right handed system. This motion corresponds to a rotation about ‘2’JCS1,2. γ (adduction–abduction): Angle between ‘2’JCS1,2 and ‘2’JCS2. g ⬎ 0, when (‘2’JCS1,2, ‘2’JCS2, ‘3’JCS2) form a right handed system. This motion corresponds to a rotation about ‘3’JCS2. The tibial rotation is defined by the g Bryant angle of JCS1 in relation to the JCS2 of the tibiotalar joint. This definition makes the tibial rotation axes fixed to the tibia. The mat deformation at the forefoot area was calculated as the mean value of the vertical coordinates of points 9, 10 and 11. In the same manner, the mat deformation at the rearfoot area was calculated as the mean value from points 15, 16 and 17. The EMG-data were rectified and smoothed using a second-order Butterworth lowpass filter with a cut-off frequency of 10 Hz [13]. The
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resulting linear envelope EMG data were normalized as follows: EMGNk ⫽
EMGFk ·100 EMGmax,k
(1)
EMGNk: Normalized EMG-Data from k-Muscle EMGFk: Linear envelope EMG-Data from k-Muscle EMGmax,k: Maximum linear envelope EMG-Data from k-Muscle of each athlete during the landing from 1.0 m. The pre-activation time (PAtime) (from onset of muscle activity until touch down), the integral of the pre-activation phase (IEMGPA), the integral of the landing phase (IEMGLA, 300 ms after touchdown) and the maximum of the EMG-activity (EMGmax) were all calculated from the normalized EMG data. The onset for the pre-activation time of each muscle was considered to be at the point where the normalized EMG value exceeded the mean value plus three standard deviations of the normalized EMG signal when the given muscle was relaxed. The observation window for the relaxed muscle signal was 200 ms. The magnitude of the EMG signal (RMS, root mean square) was calculated from the raw EMG data from onset of EMG activity to 300 ms after touch down. The differences between the three falling heights were checked using a non parametric test for several dependent samples (Friedman-test). At those parameters where differences were found a nonparametric test (Wilcoxontest) and a parametric t-test for two dependent samples were applied to assess the differences between falling heights. The level of significance was set at p ⬍ 0.05. 2.5. Sensitivity analysis The aim of the sensitivity analysis was to check the influence of the variation of selected input parameters from the model on the resulting data. The input parameters that were systematically varied, were the coordinates of the origin from all three joints (TTJ, TNJ, CCJ). These were changed ±5% of their original values in each direction. Then the motion was calculated again. Six variations per joint were considered. The results of the sensitivity analysis can be seen at Fig. 3. The maximal deviations were: for the tibiotalar joint approximately 1.87°, for the talonavicular joint approximately 1.98°, and for the calcaneocuboid joint approximately 2.01°.
3. Results During the first 70–80 ms of the landing, the tibiotalar joint everted, dorsiflexed and abducted; i.e. the foot pro-
Fig. 3. Variation of the angles of all three considered joints due to changing the origin of the corresponding joint coordinate system (the bold line represents the original values) TTJ: tibiotalar joint; TNJ: talonavicular joint; CCJ: calcaneocuboid joint; Ev–Inv: eversion-inversion; Dor–Pl: dorsi–plantar flexion; Add–Abd: adduction–abduction
nated (Fig. 4). During the first 100 ms of the landing the tibia displayed an inwards rotation with respect to the rearfoot and then showed a plateau (Fig. 5). At the tibiotalar joint the maximal joint excursion was not influenced by the different falling heights (Table 2). The maximal tibial rotation during landing was not altered either by
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Fig. 4. Eversion-inversion, dorsal flexion-plantar flexion and adduction-abduction for the three joints (mean, n = 6) during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) TTJ: Tibiotalar joint, TNJ: Talonavicular joint, CCJ: Calcaneocuboid joint
changing the falling height (Table 3). No significant differences (p ⬍ 0.05) in the studied parameters could be found (Tables 2 and 3). The mean maximal eversion was about 8–9° and the maximal tibia rotation was between 9 and 11°. The kinematics at the talonavicular joint showed an eversion and a dorsiflexion. The maximal joint excursion at the talonavicular joint was found not to be influenced by the different falling heights (Table 2). The mean maximal eversion at this joint was about 3–5°. At the calcaneocuboid joint the eversion was much higher compared to the talonavicular joint (Fig. 4) and it showed to be influenced by the different falling heights (Table 2). At falling height 3 (2.0 m) the eversion angles reached values up to 17° which is significantly (p ⬍ 0.05) higher than the values attained when falling from height 1 (1.0 m, Table 2). As expected, falling height also influenced the maximal mat deformation as well under the forefoot as under the rearfoot (Fig. 6, Table 3). The deformation at the forefoot is always higher and reached values up to 17.5 cm (Table 3). The EMG activity of the five studied muscles is represented in Fig. 7. All muscles were active for more than 90 ms before touchdown (Tables 4 and 5). The activation of the gastrocnemius medialis is notable. This muscle was very active during pre-activation and the maximal
EMG-activity was reached near touchdown (Fig. 7). After touchdown its activity decreased. On the other hand, the vastus lateralis (knee extensor) reached its maximal activity about 80–90 ms after touchdown. The hamstrings also showed maximal activity before touchdown (Fig. 7). The activity pattern of all muscles was similar for all three falling heights, but the activity level was influenced. The IEMG during pre-activation and during the landing phase, the maximal EMG-activity and the RMS all showed significantly (p ⬍ 0.05) higher values for all muscles, when falling from height 3 (2.0 m, Tables 4 and 5). The differences in the IEMG during the pre-activation and the landing phases were about 146% and 87%, respectively. For the maximal EMG activity and the RMS the differences were up to 76% and 81%. However, the pre-activation time did not show any statistically significant (p ⬍ 0.05) differences, except for the hamstrings (Table 5).
4. Discussion The main results of this study were: (a) The falling height does not show any influence on the kinematic of the tibiotalar and the talonavicular joints during landing, (b) the eversion at the calcaneocuboid joint increases with increasing falling height and (c) when augmenting
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Fig. 5. Rotation of the tibia (mean ± SD, n = 6) during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m)
falling height, the myoelectric activity of the muscles of the lower limb increases during the pre-activation phase as well as during the landing itself. The mean maximal eversion values for the tibiotalar joint were about 8–9°, which is close to the range of values reported for running in 3D analyses [14,15]. The fairly lower maximal eversion angles during running (mean value about 4°) reported by van Gheluwe et al. [16]) and Stacoff et al. [3,4] can be explained as follows: (a) The ground reac-
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tion forces when landing from higher than 1.0 m are much higher (five times bodyweight per leg, [6]) as those occurring while running at paces from 2.5 to 4.5 m/s (2.3–3.0 times bodyweight, [17]). In this manner the higher ground reaction forces could be made responsible for the higher eversion, (b) the individual differences and hence the subject sample can also influence the maximal values [3,4] and (c) the position of the foot at touchdown, which is different between running and landing [3,4,16], can change the maximal eversion during contact time. Despite increasing falling height up to 2.0 m, the maximal eversion at the tibiotalar joint and the maximal inward rotation of the tibia were not significantly affected. This result raises a question about the suggestion made by Stacoff et al. [4] pointing out that the motion at the tibiotalar joint could be changed by higher ground reaction forces. Despite the fact that ground reaction forces were not measured for this study, it is reasonable to suppose that by increasing falling height, the ground reaction forces are also increased [9,10,18]. This is also supported by the higher deformation of the mat under the forefoot as well as under the rearfoot (Table 3). Nevertheless the maximal angular excursion at the tibiotalar joint was not altered. The changes in EMG-activity of the muscles of the lower limb support the proposal from Stacoff et al. [4], stating that muscle activity should be taken into account to help explaining some phenomena in the motion of the foot. All observed muscles showed an increased myolectrical activity during pre-activation as well as during the landing itself when increasing falling height. Tibialis anterior and peroneus longus demonstrate a similar behavior while landing. Both are active before touchdown and reach their maximal activity about 150 ms after ground contact (Fig. 7). The tibialis anterior functions as a dorsiflexor and invertor [19], its higher activation when falling from height3 (2.0 m) may prevent an excessive eversion at the tibiotalar joint. The peroneus longus, in addition to its plantarflexing function, provides stability to the subtalar joint [8]. In general also the other plantarflexor muscles as for example the gastrocnemius medialis, can contribute to the stabiliz-
Table 2 Maximal joint motion [degrees, mean (SD), n = 6] at the tibiotalar, talonavicular, and calcaneocuboid joints of the left foot during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) Parameter Tibiotalar joint H1: 1.0 m amax bmax ⌬gSmax
H2: 1.5 m
Talonavicular joint H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
Calcaneocuboid joint H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
7.90 (3.20) 9.29 (3.45) 7.99 (3.20) 1.50 (4.32) 5.46 (4.56) 3.73 (4.67) 11.36 (4.25) 14.59 (4.01) 17.32 (4.18)a 13.19 (5.44) 15.81 (4.21) 18.85 (8.29) 10.08 (5.35) 10.67 (4.57) 13.50 (6.26) 13.43 (6.74) 13.86 (5.38) 16.21 (6.09) 9.92 (2.37) 10.78 (4.61) 13.69 (4.17) 9.23 (4.54) 9.12 (4.61) 7.06 (3.99) 5.51 (2.24) 7.42 (4.18) 7.50 (3.43)
αmax: Maximal eversion. βmax: Maximal dorsiflexion. ⌬γSmax: Adduction-abduction amplitude until maximum of the mat deformation. a Statistically significant (p ⬍ 0.05) difference between height1 and height3.
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Table 3 Maximal rotation of the tibia and maximal mat deformation [mean (SD), n = 6] of the left foot during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) Parameter
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
θmax (°) ⌬Srearfoot (cm) ⌬Sforefoot(cm)
9.91 (4.11) 12.55 (0.75) 14.35 (0.82)
8.42 (3.18) 15.67 (1.12)a 16.90 (0.57)a
11.59 (2.39) 16.80 (1.15)b 17.47 (0.99)b
θmax: Maximal tibiarotation. ⌬Srearfoot: Mat deformation at the rearfoot area. ⌬Sforefoot: Mat deformation at the forefoot area. a Statisticaly significant (p ⬍ 0.05) difference between height1 and height2. b Statisticaly significant (p ⬍ 0.05) difference between height1 and height3.
Fig. 6. Mat deformation over time (mean ± SD, n = 6) under the left fore- and rearfoot during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m)
ation of the tibiocalcaneal joint via co-contraction together with the tibialis anterior and the peroneus longus [8,20]. From this point of view, it can be argued that the higher muscle activity around the ankle when falling height is increased, improves the stability of the tibiotalar joint. This would explain that the kinematics at this joint remain unaltered during landing. The vastus lateralis and the hamstrings also show increased myoelectric activity at greater falling heights. As the function of the vastus lateralis is to extend the knee, a higher activity was expected because of greater falling heights causing higher moments and a higher energy to be absorbed [10]. It has also been reported [20] that the vastus lateralis may contribute to the control of the tibial rotation. On the other hand, the hamstrings, apart of being knee flexors and hip extensors, also contribute to the regulation of tibia rotation [20,21]. Again it seems as if the lack of differences in maximal tibia rotation when changing falling height is due to the ability of the muscles to improve joint stability and hence to control tibia rotation. Except for the hamstrings, no differences in pre-activation times were found. This
means that rather than the instant of activation, it is more likely that the level of activation is carrying a leading role in joint stabilization. What we can say is that the athletes adjust their behavior to the expected landings and are able to stabilize the tibiotalar joint in a manner that its motion remains within a restricted range. A coupling effect between calcaneus and tibia has often been reported in the literature [2,5,22]. Hintermann and Nigg [2,5] found a higher coupling coefficient between inversion and external rotation of the tibia than between eversion and internal tibia rotation (in vitro). On the other hand, Stacoff et al. [22] reported for in vivo running that, the coupling coefficient between eversion and internal rotation of the tibia was higher than between inversion and external tibial rotation. They also reported that the coupling between the calcaneus and the tibia increased from the unloading to the loading phase of running [22]. At the landings the calcaneus everts during the first 70–80 ms while the tibia shows an internal rotation (Figs. 5 and 6). Afterwards, despite the fact that the calcaneus inverts, the tibia still rotates inwards, reaching a plateau after about 100 ms (Fig. 5). This
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Fig. 7. Normalized EMG-activation (mean, n = 6) during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m, the vertical line indicates the instant of touch-down) GM: gastrocnemius medialis; TA: tibialis anterior; PL: peroneus longus; VL: vastus lateralis; HA: hamstrings
means that no coupling effect between calcaneus inversion and the external rotation of the tibia takes place during this phase. It seems as if the described transmission effects seen in vitro between calcaneus and tibia [2,5], are much more complex and task specific in vivo, depending on the kind of motion. For the landings, maximal eversion is achieved about the same time as maximal mat deformation (Figs. 4 and 6) which is also about the same time as maximal ground reaction force [18]. Later on during the landing, the knee joint keeps moving anterior and medially in relation to the tibiotalar joint and the tibia keeps rotating inwards. It seems as if the ongoing internal rotation of the tibia is related to the knee motion during this phase. During the landing, the talonavicular and the calcaneocuboid joints evert and dorsiflex with respect to the rearfoot. Similar to the tibiotalar joint, maximal joint
541
excursions at the talonavicular joint were not influenced by changes in falling height. On the contrary, differences were found at the calcaneocuboid joint. When comparing falling height 1 (1.0 m) with falling height3 (2.0 m) the maximal eversion rises up to 52%. Using the actual version of the model it is not possible to achieve a quantification of the risk of injury by calculating the load on the calcaneocuboid joint. The peroneus longus, which is acting on the calcaneocuboid joint, demonstrates an increased myoelectric activity during the landing phase. The increased myoelectric activity of the peroneus longus and the higher eversion at the calcaneocuboid joint induced by a greater falling height can influence both the contact force and the contact area and hence the stress at the calcaneocuboid joint. At this point it may be speculated that, the higher eversion at the calcaneocuboid joint might be important for the impact absorption at the beginning of the contact phase and be rated as positive for landing performance. However, such a reasoning does not seem to be very accurate, because the higher eversion is only found at the calcaneocuboid joint (not at the other two joints) when landing from 2.0 m. It seems much more plausible that the higher eversion of the calcaneocuboid joint occurs because of the higher deformation and the deformation hollow of the mat. This explanation is further supported by the fact that, comparing stiffer and softer mats, the latter while providing a better impact absorption, cause higher eversions at the calcaneocuboid joint during landings from the same height, because of a higher mat deformation [18]. From this point of view it seems as if the motion at the mid- and forefoot is an important issue when studying the collision between athlete and mat. In conclusion, maximal joint excursions at the tibiotalar joint, at the talonavicular joint and the maximal inward rotation of the tibia are not influenced by an increase in falling height up to 2.0 m. The muscles of the lower extremities are capable of stabilizing these joints, actively restricting their maximal motion by means of higher activation levels before and after touchdown. Maximal eversion at the calcaneocuboid joint increases about 52% when landing from 2.0 m. Even though this is not directly proving that, the observed higher eversion might lead to injury, it is still true that, the calcaneocuboid joint is the only joint, from all three considered, whose motion is not actively restricted by the athletes.
Acknowledgements
This project has been supported by the BISp (Federal Institute for Sport Science Germany).
1.80 (0.86) 17.24 (3.60) 100 (–) 87 (46) 56.44 (10.37)
5.40 (1.46) 11.88 (4.21) 114 (51) 139 (63) 52.64 (12.45)
7.51 (1.53)a 19.43 (5.27)a,b 176 (55)a,b 112 (49) 79.29 (16.43)a,b
5.12 (1.99) 10.41 (3.68) 100 (–) 110 (49) 43.72 (8.43)
H1: 1.0 m
H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
TA
GM
2.70 (1.15) 22.79 (3.14)a 122 (18)a 99 (46) 71.17 (8.09)a
H2: 1.5 m
GM: Gastrocnemius medialis. TA: Tibialis anterior. PL: Peroneus longus. a Statistically significant (p ⬍ 0.05) difference between height1 and height2, height1 and height3. b Statistically significant (p ⬍ 0.05) difference between height2 and height3.
IEMGPA (% s) IEMGLA (% s) EMGmax (%) PAtime (ms) RMS (mV)
Parameter
3.51 (0.37)a 23.70 (3.31)a 131 (11)a 96 (24) 75.59 (8.56)a
H3: 2.0 m
3.92 (2.71) 14.78 (3.27) 100 (–) 120 (68) 53.61 (10.34)
H1: 1.0 m
PL
5.56 (3.68) 19.78 (7.55) 111 (52) 105 (30) 65.42 (18.75)
H2: 1.5 m
7.91 (4.42)a,b 22.44 (9.47)a 126 (55) 139 (57) 80.47 (22.96)a
H3: 2.0 m
Table 4 Integrated EMG during the pre-activation phase (IEMGPA), integrated EMG during the landing phase (IEMGLA), maximum EMG-activity (EMGmax), pre-activation time (PAtime), and root mean square (RMS) [mean (SD), n = 6] during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m)
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Table 5 Integrated EMG during the pre-activation phase (IEMGPA), integrated EMG during the landing phase (IEMGLA), maximum EMG-activity (EMGmax), pre-activation time (PAtime), and root mean square (RMS) [mean (SD), n = 6] during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) Parameter
IEMGPA (% s) IEMGLA (% s) EMGmax (% ) PAtime (ms) RMS (mV)
VL
HA
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
1.58 (1.02) 15.09 (2.80) 100 (–) 160 (69) 46.84 (3.10)
2.95 (1.35) 18.87 (5.29) 131 (23)a 175 (54) 59.70 (12.82)
3.89 (1.15)a 21.50 (6.32)a 161 (29)a,b 174 (45) 68.10 (14.73)a
4.97 (1.67) 14.96 (4.74) 100 (–) 124 (43) 52.45 (10.64)
4.57 (2.35) 13.65 (7.67) 93 (35) 132 (47) 48.17 (16.27)
7.61 (1.41)a,b 17.54 (5.19) 145 (39)a,b 164 (48)a,b 63.87 (15.37)a,b
VL: Vastus lateralis. HA: Hamstrings. a Statistically significant (p ⬍ 0.05) difference between height1 and height2, height1 and height3. b Statistically significant (p ⬍ 0.05) difference between height2 and height3.
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A. Arampatzis et al. / Journal of Electromyography and Kinesiology 13 (2003) 533–544 Gaspar Morey Klapsing was born in 1971. He graduated in sport sciences in 1994 (Spain). For 2 years he enjoyed a grant at the Institute of Biomechanics in Valencia (Spain). In 1995 he moved to Cologne (Germany) where he joined the biomechanics research group lead by Prof. Dr. Bru¨ ggemann at the German Sport Universtiy of Cologne. Still in the same group, he is doing his PhD thesis in the field of joint stability. The main research areas he is involved in are: joint stability, movement analysis and muscle mechanics.
Gert-Peter Bru¨ ggemann completed his studies in sport and mathematics in 1976. He completed his doctorate work in Biomechanics at the Johann-Wolfgang-Goethe-University in Frankfurt, Germany in 1980. In 1983 ws named head of the Department of Track and Field and Gymnastics department and in 2000 he became Chair of the Biomechanics Department at the German Sport University of Cologne. His main research interests are biomechanics of elite and normal sports, occupational biomechanics and biomechanics of the spine.
The effect of falling height on muscle activity and foot motion during landings Adamantios Arampatzis ∗, Gaspar Morey-Klapsing, Gert-Peter Bru¨ggemann Institute for Biomechanics, German Sport University of Cologne, Carl-Diem-Weg 6, 50933 Cologne, Germany Received 10 July 2002; received in revised form 24 April 2003; accepted 1 May 2003
Abstract The aims of this study were: (a) to examine the effect of falling height on the kinematics of the tibiotalar, talonavicular and calcaneocuboid joints and (b) to study the influence of falling height on the muscle activity of the leg during landings. Six female gymnasts (height: 1.63 ± 0.04 m, weight: 58.21 ± 3.46 kg) participated in this study. All six gymnasts carried out barefoot landings, falling from 1.0, 1.5 and 2.0 m height onto a mat. Three genlocked digital high speed video cameras (250 Hz) captured the motion of the left shank and foot. Surface electromyography (EMG) was used to measure muscle activity (1000 Hz) from five muscles (gastrocnemius medialis, tibialis anterior, peroneus longus, vastus lateralis and hamstrings) of the left leg. The kinematics of the tibiotalar, talonavicular and calcaneocuboid joints were studied. The lower-leg and the foot were modelled by means of a multibody system, comprising seven rigid bodies. The falling height does not show any influence on the kinematics neither of the tibiotalar nor of the talonavicular joints during landing. The eversion at the calcaneocuboid joint increases with increasing falling height. When augmenting falling height, the myoelectric activity of the muscles of the lower limb increases as well during the preactivation phase as during the landing itself. The muscles of the lower extremities are capable of stabilizing the tibiotalar and the talonavicular joints actively, restricting their maximal motion by means of a higher activation before and after touchdown. Maximal eversion at the calcaneocuboid joint increases about 52% when landing from 2.0 m. 2003 Elsevier Ltd. All rights reserved. Keywords: Modelling; Rearfoot kinematics; Forefoot kinematics; Eversion; Tibial rotation; Foot stability; Mat deformation; EMG-activity
1. Introduction In the literature it is reported that, an excessive eversion at the ankle joint and an excessive internal rotation of the tibia during running may lead to overload and injury at the foot and the knee [1,2]. As an example, an excessive eversion has been associated to Achilles tendon diseases and an excessive tibial rotation has been associated to patellofemoral pain syndrome [3,4]. It has also been suggested that eversion of the ankle joint may be induced by ground reaction forces [5] and that higher ground reaction forces can alter this eversion [4]. In gymnastic landings, the ground reaction forces reach values above 10 times bodyweight [6] which may lead to an overload of the lower extremities. On the other hand, muscle activity and enhanced muscle strength are
∗
Corresponding author. Fax: +49-221-497-3454. E-mail address: [email protected] (A. Arampatzis).
1050-6411/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1050-6411(03)00059-2
able to reduce the eversion at the ankle joint, protecting it from excessive motion [7,8]. Falling height has an effect on ground reaction forces [9,10] and on the myoelectric activity of the muscles of the lower limb [9]. All these observations point towards the potential influence that falling height might have on ankle joint motion, leading to excessive joint excursions. They also show that the muscles of the lower limb exhibit a higher myoelectric activity which in turn may result in a higher joint stability. Therefore it can be hypothesized that the muscles, by means of a higher activation, could be able to restrict the excessive eversion of the ankle joint and the excessive tibia-rotation induced by an increased falling height. Whether or not changes in eversion of the ankle joint or in tibia rotation are induced by falling height has not yet been studied. Furthermore, recent studies [3] mention that midfoot and forefoot kinematics may be more important than those of the calcaneus for understanding orthotic effects. The motion of the midfoot or the forefoot during landings have not yet been
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studied either. Therefore the aims of this study were: (a) to examine the effect of falling height on the kinematics of the tibiotalar, talonavicular and calcaneocuboid joints using a shank–foot model and (b) to study the influence of falling height on the activity of leg muscles during landings.
3. Tuberositas naviculare (most medial point) 4. Os Cuboideum (diagonal superior to the basis of the fifth metatarsal) 5. Malleolus medialis (most medial point) 6. Malleolus lateralis (most lateral point) 7. Condilus medialis tibiae (most medial point) 8. Caput fibula (most lateral point)
2. Methods
Other markers
2.1. Experimental protocol
9. Caput metatarsale I (medial superior) 10. Caput metatarsale V (lateral superior) 11. Caput metatarsale II-III (between second and third metatarsal heads) 12. Metatarsus I (more proximal) 13. Metatarsus V (more proximal) 14. Os naviculare (on the instep) 15. Calcaneus medial (more anterior) 16. Calcaneus medial (more posterior) 17. Calcaneus lateral 18. Fascies tibiae
Six female gymnasts (height: 1.63 ± 0.04 m, weight: 58.21 ± 3.46 kg), active members of the university gymnastics team, participated in this study. The six gymnasts performed barefoot landings falling from 1.0, 1.5 and 2.0 m height onto a mat. The order of the falling heights was systematically changed among subjects. The first and the fourth gymnasts started the experiment with 1.0 m height and then continued with the 1.5 and 2.0 m heights. The second and the fifth gymnasts started with the 1.5 m height and finally the third and the sixth gymnasts started with the 2.0 m height. The size of the mat was 200 × 200 × 30 cm3. The mechanical properties of the mat (stiffness and damping) was similar to those used in gymnastic training and competition. Three genlocked digital high speed video cameras (250 Hz) captured the motion of the left shank and foot. Eighteen reflective markers were attached to the left shank and foot (Fig. 1). Eight markers were fixed on pre-defined anatomical landmarks to allow the definition of the joint coordinate systems. The remaining markers were placed on not strictly defined anatomical positions but rather on locations were lesser skin movements were expected. Below is a list of the marker locations: Bony landmarks 1. Caput metatarsale I (most medial point) 2. Caput metatarsale V (most lateral point)
Fig. 1.
The video sequences were digitised using the automatic tracking option from the “Peak Motus” system. When marker reflection was not good enough for automatic tracking, those points were digitised manually. Those trials where a marker was hidden (for example by arm movement), were excluded from the analysis. All three cameras covered a volume of approximately 60 x 60 x 60 cm3. A 30 x 30 x 30 cm3 cube was used to calibrate the cameras. To estimate the accuracy of the measurement 11 points from the calibration frame having known coordinates were digitised. These points were different to those used for calibration. All points were manually digitised and their coordinates calculated for 14 different calibrations. The absolute differences between real and measured coordinates ranged from 0.59 ± 0.06 to 2.06 ± 0.20 mm. A former estimation of the accuracy was done by considering the distance
Medial, front and lateral view of the marker placement used to define the shank–foot model
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between both malleolar markers during landing. This was compared to the same distance as calculated from the reference sequence. The malleoli were chosen because almost no deformation and therefore no change in the distance between them is expected. The absolute observed change was ±3 mm. Bipolar EMG leadoffs, with pre-amplification (bandwidth 10–500 Hz), were used to record muscle activity. Adhesive surface electrodes (Ag/AgCl) with an electrolytic gel interface and a pickup surface of 0.8 cm2 (blue sensor-Medicotest Denmark) were positioned above the midpoint of the muscle belly. The inter-electrode distance was 2 cm and electrodes were placed parallel to the presumed direction of the muscle fibers. The electrodes were further secured to the skin with elastic tape together with the pre-amplifier to reduce motion artefacts. The skin was carefully prepared (shaved and cleaned with alcohol) to reduce skin impedance. The studied muscles were: gastrocnemius medialis (GM), tibialis anterior (TA), peroneus longus (PL), vastus lateralis (VL) and hamstrings (HA). Muscles were identified by palpation. The EMG signal was recorded at 1000 Hz sampling frequency. Before the experiment started, the EMG signal for each muscle was checked online for artefacts due to mechanical causes by passively shaking the leg. Additionally, several tests of muscle activity were undertaken to determine whether a good signal was obtained from each muscle. The test included isometric contractions for each muscle group and one and two legged hopping. The preparation was renewed when such artefacts were observed. All landings were performed within one testing period, and no electrode replacement was necessary during the measurements. The synchronization of the kinematic and EMG data was done by starting the measurement systems with a common trigger. 2.2. Reference measurement Foot motion was determined with reference to a neutral position (Fig. 1). To define the neutral position, the left foot and shank from each subject were placed in an inertial reference coordinate system (RCS). The RCS had axis 1 pointing forward, axis 2 in mediolateral direction and axis 3 being vertical pointing towards the ground. The plane defined by axis 1 and 2 was parallel to the ground. The neutral position of the shank and foot was defined as follows: the shank was vertical (tip of the lateral malleolus directly below the tip of the caput fibula with no lateral inclination) corresponding to the direction of the third axis of the RCS. The foot was flat on the ground, its longitudinal axis (Tuberositas calcanei–Caput metatarsale III) parallel to the first axis of the RCS and the medial aspect of the foot pointing in direction of axis 2 from the RCS. All 18 markers were filmed in this neutral position using 3 cameras (50 Hz) to calculate their 3D coordinates.
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2.3. The shank–foot model The lower-leg and the foot were modelled by means of a multi-body system, comprising seven rigid bodies (Fig. 2). The software used for modelling purposes was the simulation software “alaska” (advanced lagrangian solver in kinetic analysis, version 3.0, Chemnitz, [11]). For the elaboration of the model special attention was given to the functional anatomy of the foot [12]. The definition of the model is represented in Table 1. The talocalcaneal and the two metatarsophalangeal joints were not used in the present study. We did not consider the talocalcaneal joint, because it is very difficult to identify adequate points on the talus. The following constraints were imposed for the whole motion process: No motion at the three last cited joints was allowed. Due to the simplifications done in the model, the tibiotalar joint included the motion of both, the tibiotalar and the talocalcaneal joints. The talonavicular joint represents the motion occurring between the medial forefoot and the rearfoot and in the same fashion the calcaneocuboid joint represents the motion between the lateral forefoot and the rearfoot. This should clarify that, the reported data were calculated by means of a model and do not exactly represent the motion of the bones of the foot. However, to our belief, the model allows to examine the effect of different falling heights on forefoot and rearfoot motion during landings. For each joint, two joint coordinate systems (JCS) attached to each of the connected segments were defined. The JCS were defined in the neutral position using the above-mentioned bony landmarks (markers 1 to 8). The definition of each JCS is described below: 2.3.1. Tibiotalar joint (TTJ) JCS1: Origin was set at the midpoint of the line joining both malleoli. Axis 3 is defined by the line joining
Fig. 2.
Shank–foot model
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Table 1 Definition of the segments and joints of the shank–foot model Segments
Bones
Joints
Connected segments
Degree of freedom
Segment Segment Segment Segment
Tibia and fibula Talus Calcaneus Os naviculare, three cuneiformi, and metatarsals I,II,III Cuboid and metatarsals IV,V Phalanges I,II,III Phalanges IV,V
Free joint Tibiotalar joint Talocalcaneal joint Talonavicular joint
Space–segment1 Segment1–segment2 Segment2–segment3 Segment2–segment4
6 3 1 3
Calcaneocuboid joint Metatarsophalan-geal joint 1 Metatarsophalan-geal joint 2
Segment3–segment5 Segment4–segment6 Segment5–segment7
3 (ball-socket joint) 1 (rotational joint) 1 (rotational joint)
1 2 3 4
Segment5 Segment 6 Segment 7
the origin with the midpoint between landmarks 7 and 8. Axis 3 points downwards. Axis 2 is orthogonal to axis 3 and contained in the plane defined by axis 3 and the line joining the malleoli. Axis 2 points towards medial. Axis 1 results from the cross product of axes 3 and 2. JCS2: Results from moving the RCS to the origin as defined for JCS1. 2.3.2. Talonavicular joint (TNJ) JCS1: Results from moving the RCS to the origin, which is located at the level of landmark 3, at the midpoint of the 3/5 of the mediolateral distance between Tuberositas naviculare and Os cuboideum. JCS2: Same origin as JCS1. Axis 2 corresponds to axis 2 of the RCS transported to the origin. Axis 1 is orthogonal to axis 2 and contained in the plane defined by axis 2 and the line joining landmarks 1 and 3. Axis 3 results from the cross product of axes 1 and 2. 2.3.3. Calcaneocuboid joint (CCJ) JCS1: Results from moving the RCS to the origin which is located at the level of the Os cuboideum, at the midpoint of the 2/5 of the mediolateral distance between Os cuboideum and tuberositas naviculare. JCS2: Same origin as JCS1. Axis 2 corresponds to axis 2 of the RCS transported to the origin. Axis 1 is orthogonal to axis 2 and contained in the plane defined by axis 2 and the line joining landmarks 2 and 4. Axis 3 results from the cross product of axes 1 and 2. Markers 9–18 were fixed onto the segments of the model, using their 3D coordinates from the reference measurement in neutral position. These markers (9–18) plus both malleoli were used for the dynamic tracking. The remaining six markers were detached before performing the landings. The 12 markers kept were tracked in space during the analysis of the landings. Their 3D coordinates allowed the calculation of the model motion and hence, the motion at the tibiotalar, calcaneonavicular and calcaneocuboid joints as defined above. Segment 1 contains markers 5, 6 and 18, segment 2 markers 15, 16 and 17, segment 3 markers 9, 12 and 14 and segment 4 markers 10, 11 and 13. In an attempt to account for the relative motion of the markers caused by soft tissue
(free joint) (ball-socket joint) (rotational joint) (ball-socket joint)
movements and deformation, the markers were attached to the model using 3D linear spring damping elements. This method does not harm the constraints of the model. From 106 N/m on, the spring constant chosen for the tracking gives back stable coordinates without oscillation. Based on experience, the damping was set a hundredfold lower. For this application the spring constant was set to k = 106 N / m and the damping constant was set to b = 104 N s / m. 2.4. Data analysis The kinematics of the tibiotalar, talonavicular and calcaneocuboid joints, were defined by the orientation of the second bone coordinate system with respect to the first one. Eversion–inversion, dorsi–plantar flexion and adduction–abduction are defined by the bryant angles (α,β,γ) as follows: α (eversion–inversion): Angle between the second axis of JCS1 (‘2’JCS1) and the nodal line ‘3’JCS2 × ‘1’JCS1. a ⬎ 0, when (‘2’JCS1, ‘3’JCS2 × ‘1’JCS1, ‘1’JCS1) form a right handed system. This motion corresponds to a rotation about the first axis of JCS1 (‘1’JCS1). This rotation transfers JCS1 in JCS1,2. β (dorsal–plantar flexion): Angle between ‘3’JCS1 and ‘3’JCS2 b ⬎ 0 when (‘3’JCS1,2, ‘3’JCS2, ‘2’JCS1,2) form a right handed system. This motion corresponds to a rotation about ‘2’JCS1,2. γ (adduction–abduction): Angle between ‘2’JCS1,2 and ‘2’JCS2. g ⬎ 0, when (‘2’JCS1,2, ‘2’JCS2, ‘3’JCS2) form a right handed system. This motion corresponds to a rotation about ‘3’JCS2. The tibial rotation is defined by the g Bryant angle of JCS1 in relation to the JCS2 of the tibiotalar joint. This definition makes the tibial rotation axes fixed to the tibia. The mat deformation at the forefoot area was calculated as the mean value of the vertical coordinates of points 9, 10 and 11. In the same manner, the mat deformation at the rearfoot area was calculated as the mean value from points 15, 16 and 17. The EMG-data were rectified and smoothed using a second-order Butterworth lowpass filter with a cut-off frequency of 10 Hz [13]. The
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resulting linear envelope EMG data were normalized as follows: EMGNk ⫽
EMGFk ·100 EMGmax,k
(1)
EMGNk: Normalized EMG-Data from k-Muscle EMGFk: Linear envelope EMG-Data from k-Muscle EMGmax,k: Maximum linear envelope EMG-Data from k-Muscle of each athlete during the landing from 1.0 m. The pre-activation time (PAtime) (from onset of muscle activity until touch down), the integral of the pre-activation phase (IEMGPA), the integral of the landing phase (IEMGLA, 300 ms after touchdown) and the maximum of the EMG-activity (EMGmax) were all calculated from the normalized EMG data. The onset for the pre-activation time of each muscle was considered to be at the point where the normalized EMG value exceeded the mean value plus three standard deviations of the normalized EMG signal when the given muscle was relaxed. The observation window for the relaxed muscle signal was 200 ms. The magnitude of the EMG signal (RMS, root mean square) was calculated from the raw EMG data from onset of EMG activity to 300 ms after touch down. The differences between the three falling heights were checked using a non parametric test for several dependent samples (Friedman-test). At those parameters where differences were found a nonparametric test (Wilcoxontest) and a parametric t-test for two dependent samples were applied to assess the differences between falling heights. The level of significance was set at p ⬍ 0.05. 2.5. Sensitivity analysis The aim of the sensitivity analysis was to check the influence of the variation of selected input parameters from the model on the resulting data. The input parameters that were systematically varied, were the coordinates of the origin from all three joints (TTJ, TNJ, CCJ). These were changed ±5% of their original values in each direction. Then the motion was calculated again. Six variations per joint were considered. The results of the sensitivity analysis can be seen at Fig. 3. The maximal deviations were: for the tibiotalar joint approximately 1.87°, for the talonavicular joint approximately 1.98°, and for the calcaneocuboid joint approximately 2.01°.
3. Results During the first 70–80 ms of the landing, the tibiotalar joint everted, dorsiflexed and abducted; i.e. the foot pro-
Fig. 3. Variation of the angles of all three considered joints due to changing the origin of the corresponding joint coordinate system (the bold line represents the original values) TTJ: tibiotalar joint; TNJ: talonavicular joint; CCJ: calcaneocuboid joint; Ev–Inv: eversion-inversion; Dor–Pl: dorsi–plantar flexion; Add–Abd: adduction–abduction
nated (Fig. 4). During the first 100 ms of the landing the tibia displayed an inwards rotation with respect to the rearfoot and then showed a plateau (Fig. 5). At the tibiotalar joint the maximal joint excursion was not influenced by the different falling heights (Table 2). The maximal tibial rotation during landing was not altered either by
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Fig. 4. Eversion-inversion, dorsal flexion-plantar flexion and adduction-abduction for the three joints (mean, n = 6) during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) TTJ: Tibiotalar joint, TNJ: Talonavicular joint, CCJ: Calcaneocuboid joint
changing the falling height (Table 3). No significant differences (p ⬍ 0.05) in the studied parameters could be found (Tables 2 and 3). The mean maximal eversion was about 8–9° and the maximal tibia rotation was between 9 and 11°. The kinematics at the talonavicular joint showed an eversion and a dorsiflexion. The maximal joint excursion at the talonavicular joint was found not to be influenced by the different falling heights (Table 2). The mean maximal eversion at this joint was about 3–5°. At the calcaneocuboid joint the eversion was much higher compared to the talonavicular joint (Fig. 4) and it showed to be influenced by the different falling heights (Table 2). At falling height 3 (2.0 m) the eversion angles reached values up to 17° which is significantly (p ⬍ 0.05) higher than the values attained when falling from height 1 (1.0 m, Table 2). As expected, falling height also influenced the maximal mat deformation as well under the forefoot as under the rearfoot (Fig. 6, Table 3). The deformation at the forefoot is always higher and reached values up to 17.5 cm (Table 3). The EMG activity of the five studied muscles is represented in Fig. 7. All muscles were active for more than 90 ms before touchdown (Tables 4 and 5). The activation of the gastrocnemius medialis is notable. This muscle was very active during pre-activation and the maximal
EMG-activity was reached near touchdown (Fig. 7). After touchdown its activity decreased. On the other hand, the vastus lateralis (knee extensor) reached its maximal activity about 80–90 ms after touchdown. The hamstrings also showed maximal activity before touchdown (Fig. 7). The activity pattern of all muscles was similar for all three falling heights, but the activity level was influenced. The IEMG during pre-activation and during the landing phase, the maximal EMG-activity and the RMS all showed significantly (p ⬍ 0.05) higher values for all muscles, when falling from height 3 (2.0 m, Tables 4 and 5). The differences in the IEMG during the pre-activation and the landing phases were about 146% and 87%, respectively. For the maximal EMG activity and the RMS the differences were up to 76% and 81%. However, the pre-activation time did not show any statistically significant (p ⬍ 0.05) differences, except for the hamstrings (Table 5).
4. Discussion The main results of this study were: (a) The falling height does not show any influence on the kinematic of the tibiotalar and the talonavicular joints during landing, (b) the eversion at the calcaneocuboid joint increases with increasing falling height and (c) when augmenting
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Fig. 5. Rotation of the tibia (mean ± SD, n = 6) during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m)
falling height, the myoelectric activity of the muscles of the lower limb increases during the pre-activation phase as well as during the landing itself. The mean maximal eversion values for the tibiotalar joint were about 8–9°, which is close to the range of values reported for running in 3D analyses [14,15]. The fairly lower maximal eversion angles during running (mean value about 4°) reported by van Gheluwe et al. [16]) and Stacoff et al. [3,4] can be explained as follows: (a) The ground reac-
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tion forces when landing from higher than 1.0 m are much higher (five times bodyweight per leg, [6]) as those occurring while running at paces from 2.5 to 4.5 m/s (2.3–3.0 times bodyweight, [17]). In this manner the higher ground reaction forces could be made responsible for the higher eversion, (b) the individual differences and hence the subject sample can also influence the maximal values [3,4] and (c) the position of the foot at touchdown, which is different between running and landing [3,4,16], can change the maximal eversion during contact time. Despite increasing falling height up to 2.0 m, the maximal eversion at the tibiotalar joint and the maximal inward rotation of the tibia were not significantly affected. This result raises a question about the suggestion made by Stacoff et al. [4] pointing out that the motion at the tibiotalar joint could be changed by higher ground reaction forces. Despite the fact that ground reaction forces were not measured for this study, it is reasonable to suppose that by increasing falling height, the ground reaction forces are also increased [9,10,18]. This is also supported by the higher deformation of the mat under the forefoot as well as under the rearfoot (Table 3). Nevertheless the maximal angular excursion at the tibiotalar joint was not altered. The changes in EMG-activity of the muscles of the lower limb support the proposal from Stacoff et al. [4], stating that muscle activity should be taken into account to help explaining some phenomena in the motion of the foot. All observed muscles showed an increased myolectrical activity during pre-activation as well as during the landing itself when increasing falling height. Tibialis anterior and peroneus longus demonstrate a similar behavior while landing. Both are active before touchdown and reach their maximal activity about 150 ms after ground contact (Fig. 7). The tibialis anterior functions as a dorsiflexor and invertor [19], its higher activation when falling from height3 (2.0 m) may prevent an excessive eversion at the tibiotalar joint. The peroneus longus, in addition to its plantarflexing function, provides stability to the subtalar joint [8]. In general also the other plantarflexor muscles as for example the gastrocnemius medialis, can contribute to the stabiliz-
Table 2 Maximal joint motion [degrees, mean (SD), n = 6] at the tibiotalar, talonavicular, and calcaneocuboid joints of the left foot during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) Parameter Tibiotalar joint H1: 1.0 m amax bmax ⌬gSmax
H2: 1.5 m
Talonavicular joint H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
Calcaneocuboid joint H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
7.90 (3.20) 9.29 (3.45) 7.99 (3.20) 1.50 (4.32) 5.46 (4.56) 3.73 (4.67) 11.36 (4.25) 14.59 (4.01) 17.32 (4.18)a 13.19 (5.44) 15.81 (4.21) 18.85 (8.29) 10.08 (5.35) 10.67 (4.57) 13.50 (6.26) 13.43 (6.74) 13.86 (5.38) 16.21 (6.09) 9.92 (2.37) 10.78 (4.61) 13.69 (4.17) 9.23 (4.54) 9.12 (4.61) 7.06 (3.99) 5.51 (2.24) 7.42 (4.18) 7.50 (3.43)
αmax: Maximal eversion. βmax: Maximal dorsiflexion. ⌬γSmax: Adduction-abduction amplitude until maximum of the mat deformation. a Statistically significant (p ⬍ 0.05) difference between height1 and height3.
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Table 3 Maximal rotation of the tibia and maximal mat deformation [mean (SD), n = 6] of the left foot during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) Parameter
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
θmax (°) ⌬Srearfoot (cm) ⌬Sforefoot(cm)
9.91 (4.11) 12.55 (0.75) 14.35 (0.82)
8.42 (3.18) 15.67 (1.12)a 16.90 (0.57)a
11.59 (2.39) 16.80 (1.15)b 17.47 (0.99)b
θmax: Maximal tibiarotation. ⌬Srearfoot: Mat deformation at the rearfoot area. ⌬Sforefoot: Mat deformation at the forefoot area. a Statisticaly significant (p ⬍ 0.05) difference between height1 and height2. b Statisticaly significant (p ⬍ 0.05) difference between height1 and height3.
Fig. 6. Mat deformation over time (mean ± SD, n = 6) under the left fore- and rearfoot during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m)
ation of the tibiocalcaneal joint via co-contraction together with the tibialis anterior and the peroneus longus [8,20]. From this point of view, it can be argued that the higher muscle activity around the ankle when falling height is increased, improves the stability of the tibiotalar joint. This would explain that the kinematics at this joint remain unaltered during landing. The vastus lateralis and the hamstrings also show increased myoelectric activity at greater falling heights. As the function of the vastus lateralis is to extend the knee, a higher activity was expected because of greater falling heights causing higher moments and a higher energy to be absorbed [10]. It has also been reported [20] that the vastus lateralis may contribute to the control of the tibial rotation. On the other hand, the hamstrings, apart of being knee flexors and hip extensors, also contribute to the regulation of tibia rotation [20,21]. Again it seems as if the lack of differences in maximal tibia rotation when changing falling height is due to the ability of the muscles to improve joint stability and hence to control tibia rotation. Except for the hamstrings, no differences in pre-activation times were found. This
means that rather than the instant of activation, it is more likely that the level of activation is carrying a leading role in joint stabilization. What we can say is that the athletes adjust their behavior to the expected landings and are able to stabilize the tibiotalar joint in a manner that its motion remains within a restricted range. A coupling effect between calcaneus and tibia has often been reported in the literature [2,5,22]. Hintermann and Nigg [2,5] found a higher coupling coefficient between inversion and external rotation of the tibia than between eversion and internal tibia rotation (in vitro). On the other hand, Stacoff et al. [22] reported for in vivo running that, the coupling coefficient between eversion and internal rotation of the tibia was higher than between inversion and external tibial rotation. They also reported that the coupling between the calcaneus and the tibia increased from the unloading to the loading phase of running [22]. At the landings the calcaneus everts during the first 70–80 ms while the tibia shows an internal rotation (Figs. 5 and 6). Afterwards, despite the fact that the calcaneus inverts, the tibia still rotates inwards, reaching a plateau after about 100 ms (Fig. 5). This
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Fig. 7. Normalized EMG-activation (mean, n = 6) during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m, the vertical line indicates the instant of touch-down) GM: gastrocnemius medialis; TA: tibialis anterior; PL: peroneus longus; VL: vastus lateralis; HA: hamstrings
means that no coupling effect between calcaneus inversion and the external rotation of the tibia takes place during this phase. It seems as if the described transmission effects seen in vitro between calcaneus and tibia [2,5], are much more complex and task specific in vivo, depending on the kind of motion. For the landings, maximal eversion is achieved about the same time as maximal mat deformation (Figs. 4 and 6) which is also about the same time as maximal ground reaction force [18]. Later on during the landing, the knee joint keeps moving anterior and medially in relation to the tibiotalar joint and the tibia keeps rotating inwards. It seems as if the ongoing internal rotation of the tibia is related to the knee motion during this phase. During the landing, the talonavicular and the calcaneocuboid joints evert and dorsiflex with respect to the rearfoot. Similar to the tibiotalar joint, maximal joint
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excursions at the talonavicular joint were not influenced by changes in falling height. On the contrary, differences were found at the calcaneocuboid joint. When comparing falling height 1 (1.0 m) with falling height3 (2.0 m) the maximal eversion rises up to 52%. Using the actual version of the model it is not possible to achieve a quantification of the risk of injury by calculating the load on the calcaneocuboid joint. The peroneus longus, which is acting on the calcaneocuboid joint, demonstrates an increased myoelectric activity during the landing phase. The increased myoelectric activity of the peroneus longus and the higher eversion at the calcaneocuboid joint induced by a greater falling height can influence both the contact force and the contact area and hence the stress at the calcaneocuboid joint. At this point it may be speculated that, the higher eversion at the calcaneocuboid joint might be important for the impact absorption at the beginning of the contact phase and be rated as positive for landing performance. However, such a reasoning does not seem to be very accurate, because the higher eversion is only found at the calcaneocuboid joint (not at the other two joints) when landing from 2.0 m. It seems much more plausible that the higher eversion of the calcaneocuboid joint occurs because of the higher deformation and the deformation hollow of the mat. This explanation is further supported by the fact that, comparing stiffer and softer mats, the latter while providing a better impact absorption, cause higher eversions at the calcaneocuboid joint during landings from the same height, because of a higher mat deformation [18]. From this point of view it seems as if the motion at the mid- and forefoot is an important issue when studying the collision between athlete and mat. In conclusion, maximal joint excursions at the tibiotalar joint, at the talonavicular joint and the maximal inward rotation of the tibia are not influenced by an increase in falling height up to 2.0 m. The muscles of the lower extremities are capable of stabilizing these joints, actively restricting their maximal motion by means of higher activation levels before and after touchdown. Maximal eversion at the calcaneocuboid joint increases about 52% when landing from 2.0 m. Even though this is not directly proving that, the observed higher eversion might lead to injury, it is still true that, the calcaneocuboid joint is the only joint, from all three considered, whose motion is not actively restricted by the athletes.
Acknowledgements
This project has been supported by the BISp (Federal Institute for Sport Science Germany).
1.80 (0.86) 17.24 (3.60) 100 (–) 87 (46) 56.44 (10.37)
5.40 (1.46) 11.88 (4.21) 114 (51) 139 (63) 52.64 (12.45)
7.51 (1.53)a 19.43 (5.27)a,b 176 (55)a,b 112 (49) 79.29 (16.43)a,b
5.12 (1.99) 10.41 (3.68) 100 (–) 110 (49) 43.72 (8.43)
H1: 1.0 m
H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
TA
GM
2.70 (1.15) 22.79 (3.14)a 122 (18)a 99 (46) 71.17 (8.09)a
H2: 1.5 m
GM: Gastrocnemius medialis. TA: Tibialis anterior. PL: Peroneus longus. a Statistically significant (p ⬍ 0.05) difference between height1 and height2, height1 and height3. b Statistically significant (p ⬍ 0.05) difference between height2 and height3.
IEMGPA (% s) IEMGLA (% s) EMGmax (%) PAtime (ms) RMS (mV)
Parameter
3.51 (0.37)a 23.70 (3.31)a 131 (11)a 96 (24) 75.59 (8.56)a
H3: 2.0 m
3.92 (2.71) 14.78 (3.27) 100 (–) 120 (68) 53.61 (10.34)
H1: 1.0 m
PL
5.56 (3.68) 19.78 (7.55) 111 (52) 105 (30) 65.42 (18.75)
H2: 1.5 m
7.91 (4.42)a,b 22.44 (9.47)a 126 (55) 139 (57) 80.47 (22.96)a
H3: 2.0 m
Table 4 Integrated EMG during the pre-activation phase (IEMGPA), integrated EMG during the landing phase (IEMGLA), maximum EMG-activity (EMGmax), pre-activation time (PAtime), and root mean square (RMS) [mean (SD), n = 6] during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m)
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Table 5 Integrated EMG during the pre-activation phase (IEMGPA), integrated EMG during the landing phase (IEMGLA), maximum EMG-activity (EMGmax), pre-activation time (PAtime), and root mean square (RMS) [mean (SD), n = 6] during landings from height1 (1.0 m), height2 (1.5 m), and height3 (2.0 m) Parameter
IEMGPA (% s) IEMGLA (% s) EMGmax (% ) PAtime (ms) RMS (mV)
VL
HA
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
H1: 1.0 m
H2: 1.5 m
H3: 2.0 m
1.58 (1.02) 15.09 (2.80) 100 (–) 160 (69) 46.84 (3.10)
2.95 (1.35) 18.87 (5.29) 131 (23)a 175 (54) 59.70 (12.82)
3.89 (1.15)a 21.50 (6.32)a 161 (29)a,b 174 (45) 68.10 (14.73)a
4.97 (1.67) 14.96 (4.74) 100 (–) 124 (43) 52.45 (10.64)
4.57 (2.35) 13.65 (7.67) 93 (35) 132 (47) 48.17 (16.27)
7.61 (1.41)a,b 17.54 (5.19) 145 (39)a,b 164 (48)a,b 63.87 (15.37)a,b
VL: Vastus lateralis. HA: Hamstrings. a Statistically significant (p ⬍ 0.05) difference between height1 and height2, height1 and height3. b Statistically significant (p ⬍ 0.05) difference between height2 and height3.
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A. Arampatzis et al. / Journal of Electromyography and Kinesiology 13 (2003) 533–544 Gaspar Morey Klapsing was born in 1971. He graduated in sport sciences in 1994 (Spain). For 2 years he enjoyed a grant at the Institute of Biomechanics in Valencia (Spain). In 1995 he moved to Cologne (Germany) where he joined the biomechanics research group lead by Prof. Dr. Bru¨ ggemann at the German Sport Universtiy of Cologne. Still in the same group, he is doing his PhD thesis in the field of joint stability. The main research areas he is involved in are: joint stability, movement analysis and muscle mechanics.
Gert-Peter Bru¨ ggemann completed his studies in sport and mathematics in 1976. He completed his doctorate work in Biomechanics at the Johann-Wolfgang-Goethe-University in Frankfurt, Germany in 1980. In 1983 ws named head of the Department of Track and Field and Gymnastics department and in 2000 he became Chair of the Biomechanics Department at the German Sport University of Cologne. His main research interests are biomechanics of elite and normal sports, occupational biomechanics and biomechanics of the spine.