Gastrocnemius tightness on joint angle and work of lower extremity during gait

Clinical Biomechanics 24 (2009) 744–750

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Gastrocnemius tightness on joint angle and work of lower extremity during gait Jia-Yuan You a, Hsin-Min Lee a, Hong-Ji Luo b, Chwan-Chin Leu b,c, Pen-Gang Cheng d, Shyi-Kuen Wu b,* a

Department of Physical Therapy, I-Shou University, Kaohsiung County, Taiwan Department of Physical Therapy, HungKuang University, Shalu, Taichung County, Taiwan c Department of Physical Medicine and Rehabilitation, Taichung Hospital, Department of Health, Taiwan d Department of Orthopedic Surgery, Kuang-Tien General Hospital, Taichung County, Taiwan b

a r t i c l e

i n f o

Article history: Received 20 March 2009 Accepted 3 July 2009

Keywords: Muscle tightness Gastrocnemius Joint work Gait analysis

a b s t r a c t Background: Muscular tightness is a common clinical musculoskeletal disorder and is regarded as a predisposing factor for muscle injuries. In this study, a two-way mixed design ANOVA was applied to investigate the effects of the gastrocnemius tightness on the joint angle and joint work during walking. Methods: Twenty-two patients with muscular tightness of gastrocnemius muscle (<12° of ankle dorsiflexion with knee extended) and 22 age- and gender-matched subjects with normal gastrocnemius flexibility (>15° of ankle dorsiflexion with knee extended) participated in this study. The joint angle and work at hip, knee, and ankle joints during the stance phase were analyzed at two preset cadences of 100 steps/ min and 140 steps/min. Findings: Significantly greater flexion angles at hip (P = 0.025) and knee (P = 0.001) were found in the tightness group at the time of maximal ankle dorsiflexion. Significantly less work generation at knee (P = 0.034) and greater work absorption at ankle (P = 0.024) were detected in the tightness group. Interpretation: The subjects with gastrocnemius tightness revealed a compensatory gait pattern, which included the changes in the joint angles and associated work productions. The potential disturbance of the knee control and strain injuries of plantar flexors might be crucial in the clinical considerations for subjects with gastrocnemius tightness. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Muscle tightness is a common muscular dysfunction and it predisposes individuals to musculoskeletal injuries (Hertling and Kessler, 2006; Neely, 1998; Wang et al., 1993; Ekstrand and Gillquist, 1982; Kisner and Colby, 2007). Overuse, poor posture, decreased flexibility, and spasticity are all considered to contribute the muscle tightness (Hertling and Kessler, 2006; Wang et al., 1993; Ekstrand and Gillquist, 1982, 1983; Moseley et al., 2003; Baddar et al., 2002). The gastrocnemius muscle is one of the most common tight muscles found in lower extremities, which are characterized by crossing ankle and knee joints. Lack of flexibility in gastrocnemius muscle can reduce the range of motion (RoM) in the ankle dorsiflexion and knee extension (Hertling and Kessler, 2006; Neely, 1998; Wang et al., 1993; Ekstrand and Gillquist, 1982; Kisner and Colby, 2007). Limited ankle joint dorsiflexion has often been regarded to be a predisposing factor for a number of lower limb injuries including muscle strains (Ekstrand and Gillquist, 1982), plantar fasciitis (Riddle et al., 2003), Achilles tendin-

* Corresponding author. Address: Department of Physical Therapy, HungKuang University, No. 34, Chung-Chie Rd., Shalu, Taichung County 433, Taiwan. E-mail address: [email protected] (S.-K. Wu). 0268-0033/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2009.07.002

opathy (Kaufman et al., 1999; Wilder and Sethi, 2004), stress fractures (Neely, 1998; Wilder and Sethi, 2004), shin splints (Neely, 1998; Wilder and Sethi, 2004; Messier and Pittala, 1988), iliotibial band friction syndrome (Neely, 1998; Messier and Pittala, 1988), and patellofemoral syndrome (Lun et al., 2004). Ambulation is an important functional task for human locomotion and it requires complex interactions and coordination among the major joints of the body, particularly the lower extremities. The disturbance at the ankle motion resulting from muscular tightness during gait may affect not only the ankle–foot complex but also the remainder joints of the lower extremities. From a biomechanical viewpoint, previous studies have revealed the significantly different joint angles and moments during ambulation between normal subjects and neurological patients with cerebral palsy or stroke (Baddar et al., 2002; Armand et al., 2006; Maluf et al., 2004; Wren et al., 2004). Mueller et al. also found that the ankle motion in the patients with diabetes and peripheral neuropathies led to the lesser peak ankle power during terminal stance (Mueller et al., 1995). Chronic calf muscle tightness caused by the myofascial pain syndrome has been documented to increase the peak knee flexion angle and knee extensor moment during stance phase (Wu et al., 2005). Recently, Matjacic et al. artificially induced the gastrocnemius contracture of subjects to analyze the effect of a toe-walking movement. They found the significant changes in the

J.-Y. You et al. / Clinical Biomechanics 24 (2009) 744–750

ankle and knee angle trajectories, and increased ankle power absorption, as compared to normal subjects (Matjacic´ et al., 2006). Although these studies have provided valuable information about biomechanical alterations that resulted from the tightness of gastrocnemius muscle or limited ankle motion, other important parameters such as joint work or energy consumption of the lower extremities during gait have been less extensively investigated. The joint power and work can provide further information about the patterns of muscle contraction than the typical spatial– temporal measures. Joint power denotes the generation or absorption of mechanical energy by different forms of muscle concentric and eccentric contractions. The cerebral palsy patients were reported to have less power generation by the ankle plantar flexors at push-off and less power absorption by the ankle joint during midstance (Baddar et al., 2002; Olney et al., 1990). Furthermore, the work parameter integrated from the power curve over time was used to quantify the effect of both time and peak of power curves (Chen et al., 1997; Teixeira-Salmela et al., 2008). The concentric contractions of muscles were found to create positive work and generate energy to move the body segments during gait. In contrast, the eccentric contractions of muscles produce negative work and absorb energy to resist against the lengthening of muscles (Teixeira-Salmela et al., 2008; Proske et al., 2004). It is generally accepted that the eccentric contraction is one of the major mechanisms in muscle strain, for example, hamstring strain during the terminal swing of sprinting (Hertling and Kessler, 2006; Schache et al., 2009; Norkin and White, 2003). Therefore, joint work could be a parameter to assess the pattern of muscular contraction and the potential for eccentric muscle strains. As a considerable inter-subject variability has been found in the gastrocnemius flexibility of adults (Wang et al., 1993; Ekstrand and Gillquist, 1982; Moseley et al., 2003; Johanson et al., 2008), few studies have explored the role of the gastrocnemius tightness on gait performance. The purpose of this study was to investigate the effect of the gastrocnemius tightness on the joint angle and work during walking in order to better understand the compensatory movement patterns which are important for designing effective interventions for preventing injury and disabilities. 2. Methods 2.1. Subjects A total of 44 subjects served as the experimental (n = 22) and control (n = 22) groups in this study. Twenty-two adult patients, thirteen females and nine males, with the gastrocnemius muscle tightness and 22 healthy subjects age- and gender-matched were recruited and completed the study. All subjects ranged in age from 20 to 34 years, with a mean age of 22.9 years (SD = 2.5). This study was approved by an ethics committee for human research. The experimental procedures were fully explained to all the participants and the signed informed consents were obtained. The eligibility criterion for gastrocnemius tightness, which was the same as that used in a previous investigation, was the passive ankle dorsiflexion with knee fully extended less than 12° (Johanson et al., 2008). The subjects in the control group met the criterion that passive ankle dorsiflexion with knee fully extended was greater than 15°. Subjects were excluded from participation in the experiment if they had: (1) history of ankle trauma or surgery, (2) bone pathology, (3) arthritic or other inflammatory disease, (4) neurological system dysfunction, or (5) ankle or knee symptoms within 2 weeks prior to enrollment. 2.2. Range of motion (RoM) measurements The passive RoM of ankle dorsiflexion with knee fully extended was used to test the tightness condition of gastrocnemius muscle

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(Johanson et al., 2008; Norkin and White, 2003). The passive RoM of ankle dorsiflexion with knee flexed to 90° was also measured. RoM measurements were performed by an experienced physical therapist. Subjects were placed in the prone position with their foot and ankle hanging over the edge of the table. According to the standard goniometric procedures, the subtalar joint was palpated for attempting to keep it in neutral during measurement. A standard plastic goniometer (Model J00240, Lafayette Instrument Co., IN, USA) with the precision of 1° increments was used to measure the ankle RoM. The fulcrum of the goniometer was centered over the lateral malleolus. The stationary arm was aligned along the lateral midline of the fibula and the moving arm was positioned along the lateral midline of the fifth metatarsal bone. The RoM of ankle dorsiflexion was measured by passive bringing the foot toward the anterior aspect of lower leg (Johanson et al., 2008). Three trials for each measurement were recorded and the measurements were averaged to yield the representative values. The intra-examiner reliability was examined at a 2-week interval for eight subjects in the pilot study, the intraclass correlation coefficients (ICC) for measuring the ankle dorsiflexion range of motion varied between 0.88 and 0.95 (average = 0.92) and the corresponding mean absolute difference (MAD) averaged 1.2° within examiner. 2.3. Gait testing Three-dimensional motions of body segments were measured by the five camera motion analysis system (Evart 5.0, Motion Analysis Corporation, Santa Rosa, CA, USA) operating at 60 Hz sample rate. Two AMTI forceplates (Advanced Mechanical Technology, Inc., Watertown, MA, USA) were used to measure the ground reaction forces with 1000 Hz sample rate. Data collection was simultaneously triggered and synchronized before each subject stepped onto the first forceplate. The subjects were instructed to walk along the walkway at two cadences. The metronome was set at 100 steps/min and 140 steps/min, and the subjects were encouraged to match the beeps of the metronome. Before the data collection, several practice walks were allowed to habituate the subjects to the testing environment. After the testing, the results of five successful trails were collected for further analysis. Fifteen reflective markers were placed on body segments according to the anatomical positions suggested by Kadaba et al. (1990). These markers were on the sacrum top in line with the spinal plane, bilateral anterior superior iliac spines, bilateral midthighs and lateral femoral epicondyles, bilateral mid-shanks and bilateral lateral malleolus, heels and foot between 2nd and 3rd metatarsal heads. The diameter of each reflective marker was 20 mm. The position data of markers and ground reaction forces were processed with the Ortho Trak software (Motion Analysis Corporation, Santa Rosa, CA, USA) to generate the kinematic data and joint power (Power) for sequential analysis. The joint work at each joint during the stance phase was derived as the area under the power–time history curves and was partitioned into positive and negative phases. The time integral of the power measurements was computed using the trapezoidal approximation (Hansen et al., 2004; Chen et al., 1997). The positive phase of the power–time curve represented the joint work generation (Wpositive; Eq. (1)), whereas the negative phase of power–time curve represented the joint work absorption (Wnegative; Eq. (2)) ve W positi ¼ J ve W negati ¼ J

Z

tf

Power dt for Power > 0

ð1Þ

Power dt for Power < 0

ð2Þ

ti

Z

tf

ti

where J represented the joint (ankle, knee or hip), Power the joint power, and ti and tf represented the initial and final time in the stance phase, respectively.

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2.4. Statistical analyses

3.1. Joint angle

The RoM measurements included the ankle dorsiflexion ranges with knee in full extension and at 90° of flexion. The tempospatial parameters (step length, cadence, velocity, and the proportion of the stance phase), joint angle and joint work were analyzed in the gait cycle. An independent sample t-test was performed to assess the tightness condition of gastrocnemius muscle and the ankle dorsiflexion ranges between tightness and control groups. A twoway mixed design ANOVA was performed to examine the effects of group and cadence. All parameters were statistically analyzed using computer software, Statistical Package for the Social Sciences (version 11, SPSS, Chicage, IL, USA), and the values of P < 0.05 were considered significant. Whenever the main effect or interaction effect was significant, subsequent post hoc multiple comparisons with the Bonferroni procedure were used to analyses. Pearson’s correlation was performed to calculate the correlation of flexion angle between ankle and knee joints during single-limb stance phase for each subject.

The averaged time histories of the joint angles in the sagittal plane for both groups at different cadences are shown in Fig. 1. The curve patterns of joint angles at hip, knee and ankle joints were similar for both groups. However, there were greater flexion degrees at hip joint throughout the gait cycle and at knee joint during the midstance phase in the tightness group. Considering the joint angles at the time of maximal ankle dorsiflexion, the significant differences were found at hip (P = 0.025) and at knee (P = 0.001) joints between the tightness and control groups (Table 3). The subsequent analysis revealed that the tightness group had significantly greater hip and knee joint angles at both preset cadences. The hip and ankle joint angles at the time of maximal ankle dorsiflexion were also significantly affected by the preset cadences (P = 0.009 and P = 0.001, respectively). The post hoc multiple comparisons showed that both groups had the significantly greater hip flexion but smaller ankle dorsiflexion angles at the faster preset cadence of 140 steps/min. The control group had a higher negative correlation between ankle and knee motion at the cadences of 100 steps/min (r = 0.904, P = 0.001) and of 140 steps/min (r = 0.928, P = 0.001). The tightness group had less negative correlations between knee and ankle motion at the cadences of 100 steps/min (r = 0.762, P = 0.001) and of 140 steps/ min cadence (r = 0.895, P = 0.001).

3. Results The average body height and weight of the subjects in the muscle tightness group and control group are presented in Table 1. The body height and weight were not significantly different between the tightness and control groups (P = 0.796–0.825). The mean range of the ankle dorsiflexion with knee extended was significantly smaller in the tightness group than in the control group (9.0° vs. 18.7°, P = 0.001). The mean range of ankle dorsiflexion with knee flexed at 90° was not significantly different between tightness and control groups (19.5° vs. 21.6°, P = 0.053). The tempospatial parameters during different preset cadences in both groups are listed in Table 2. The two preset cadences significantly affected the actual cadence (P = 0.001), step velocity (P = 0.001), stride length (P = 0.032), and percentage of stance phase (P = 0.001) during gait cycle.

Table 1 Tempospatial parameter values grouped by tightness for each gait speed task, expressed in mean (SD). Group

Tightness group (n = 22)

Control group (n = 22)

Significant effect

Height (cm) Weight (kg) Passive RoM of ankle dorsiflexion (degree) Tightness condition of gastrocnemius muscle (degree)

166.5 (8.0) 59.4 (9.7) 19.5 (3.3)

167.0 (7.0) 60.0 (10.6) 21.6 (3.7)

P = 0.796 P = 0.825 P = 0.053

18.7 (2.0)

P = 0.001

9.0 (2.2)

3.2. Joint work The averaged power–time history curves of ankle, knee and hip joints for both groups at different cadences are presented in Fig. 2. The curve patterns of joint power in the tightness group were similar to those of control group. The work generation of the knee joint was noted to be statistically different between the tightness and control groups (P = 0.034) and the post hoc multiple comparisons revealed the significantly less knee work generation in the tightness group at the cadence of 100 steps/min (Table 3). The cadence effect on work generation was detected for each joint (all P = 0.001) and the post hoc analysis indicated that the significantly greater work generation occurred at the faster cadence in both groups. For the work absorption, the ankle joint showed the significant difference between two groups (P = 0.024) and the post hoc comparison demonstrated the significantly greater ankle work absorption in the tightness group only at the faster cadence. The cadence effect on work absorption was detected for the knee and ankle joints (both P = 0.001). The post hoc analysis revealed the significantly greater knee work absorption and less ankle work absorption at the faster cadence in both groups. 4. Discussion The present study assessed the effect of gastrocnemius tightness on joint angle and joint work of the lower extremities during

Table 2 The tempospatial parameters were grouped by tightness for different preset cadences and were expressed in mean (SD). Group

Tightness group (n = 22)

Control group (n = 22)

Preset cadence Condition

100 [1]

100 [3]

Step velocity (cm/s) Stride length (cm) Actual step cadence (steps/min) Stance phase (%)

93.1 107.9 102.8 62.3

140 [2] (6.9) (6.5) (3.6) (1.3)

128.0 110.9 138.3 61.8

(9.4) (8.5) (4.4) (1.3)

94.7 111.8 101.4 62.6

Significant main effect

Post hoc comparison (P < 0.025)

P = 0.001a P = 0.032a P = 0.001a P = 0.001a

[1,2] [3,4] [1,2] [1,2] [3,4] [1,2] [3,4]

140 [4] (8.0) (8.7) (2.8) (1.4)

128.1 113.2 136.5 61.8

(8.9) (9.1) (3.9) (1.4)

[1,2]: Significant difference between condition 1 (tightness group at 100 steps/min) and condition 2 (control group at 100 steps/min). a Cadence effect.

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40

A Joint power (Walt/kg)

Joint angle (degrees)

A

20

0

-20

0

50

100

1

0.5

0

-0.5

Percent of gait cycle

0

50

100

Joint angle (degrees)

B

80

B

60

Joint power (Walt/kg)

Percent of gait cycle

40

20

0

0

50

100

0.5

0

-0.5

-1

-1.5

Percent of gait cycle

0

50

100

Percent of gait cycle 20

C Joint power (Walt/kg)

Joint angle (degrees)

C

10

0

-10

-20

0

50

100

3

2

1

0

-1

Percent of gait cycle

0

50

100

Percent of gait cycle Fig. 1. Joint angle patterns (degrees) for each condition across the gait cycle: (A) at the hip, (B) at the knee, (C) at the ankle joint. The positive values represented the joint flexion at the hip and knee, and dorsiflexion at the ankle. The negative values represented the joint extension at the hip and knee, and plantarflexion at the ankle. Solid line, ‘-’, represented the control group at 100 steps/min of cadence. Dashed line, ‘–’, represented the tightness group at 100 steps/min of cadence. Dash-dot line, ‘--’, represented the control group at 140 steps/min of cadence. Dotted line, ‘. . .’, represented the tightness group at 140 steps/min of cadence.

gait. Our results indicated that the gastrocnemius tightness might lead to the greater hip and knee flexion angles at the time of maximal ankle dorsiflexion, the less knee work generation, and the greater ankle work absorption. The faster cadence was associated with the greater work generation at all joints, the greater work absorption at knee, and less work absorption at ankle.

Fig. 2. Joint power patterns (Walt/kg) for each condition across the gait cycle: (A) at the hip, (B) at the knee, (C) at the ankle joint. The positive values represented power generation and the negative values represented power absorption. Solid line, ‘-’, represented the control group at 100 steps/min of cadence. Dash line, ‘–’, represented the tightness group at 100 steps/min of cadence. Dash-dot line, ‘--’, represented the control group at 140 steps/min of cadence. Dotted line, ‘. . .’, represented the tightness group at 140 steps/min of cadence.

4.1. Joint angle Both groups in the present study demonstrated a similar dorsiflexion range of ankle with the knee at 90° flexion, while the tightness group had a significantly smaller ankle dorsiflexion range with the knee in full extension. Therefore, the interference effects

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Table 3 The joint angles and work of stance phase were grouped by tightness for different preset cadences, and were expressed in mean (SD). The positive values represented the joint flexion at the hip and knee, and dorsiflexion at the ankle. The negative values represented the joint extension at the hip and knee, and plantarflexion at the ankle. Group

Tightness group (n = 22)

Control group (n = 22)

Preset cadence Condition

100 [1]

100 [3]

140 [4]

8.9 (7.5) 8.7 (3.5) 13.5 (3.2)

6.7 (10.0) 9.4 (2.9) 12.3 (3.2)

140 [2]

Joint angle at the time of maximal ankle dorsiflexion Hip (degree) 2.5 0.6 (9.7) (9.9) Knee (degree) 13.1 13.3 (4.9) (4.7) Ankle (degree) 14.5 12.8 (3.6) (3.3) Joint work generation in the stance phase Hip (J/kg) 0.101 (0.056) Knee (J/kg) 0.041 (0.025) Ankle (J/kg) 0.144 (0.031)

0.159 (0.069) 0.058 (0.028) 0.177 (0.027)

0.084 (0.035) 0.058 (0.021) 0.151 (0.036)

0.135 (0.042) 0.071 (0.024) 0.172 (0.041)

Joint work absorption in the stance phase Hip (J/kg) 0.055 (0.039) Knee (J/kg) 0.055 (0.026) Ankle (J/kg) 0.147 (0.04)

0.055 (0.038) 0.109 (0.036) 0.107 (0.036)

0.076 (0.043) 0.06 (0.017) 0.128 (0.022)

0.074 (0.045) 0.108 (0.027) 0.085 (0.024)

Significant main effect

Post hoc comparison (P < 0.025)

P = 0.025a P = 0.009b P = 0.001a

[1,3] [2,4] [1,2] [3,4] [1,3] [2,4]

P = 0.001b

[1,2] [3,4]

P = 0.001b

[1,2] [3,4]

P = 0.034a P = 0.001b P = 0.001b

[1,3] [1,2] [3,4] [1,2] [3,4]

P = 0.001b

[1,2] [3,4]

P = 0.024a P = 0.001b

[2,4] [1,2] [3,4]

[1,2]: Significant difference between condition 1 (tightness group at 100 steps/min) and condition 2 (control group at 100 steps/min). a Group effect. b Cadence effect.

on the gait performance in this study might be mainly due to the muscular tightness of gastrocnemius rather than the soleus muscle, ligaments or joint capsules. The gastrocnemius muscle crosses the knee and ankle joints, and the tightness of gastrocnemius muscle may influence the kinematic patterns of lower extremities during gait. The equinus gait or toe walking resulted from the severe gastrocnemius spasticity or contracture was one of the common abnormal gait patterns in patients with cerebral palsy (Baddar et al., 2002; Armand et al., 2006; Wren et al., 2004; Matjacic´ et al., 2006). The characteristics of equinus gait are forefoot strike to initiate the gait cycle and premature plantar flexion in early stance to midstance. Nevertheless, a previous investigation demonstrated that the subjects with low gastrocnemius flexibility had a similar ankle kinematic pattern to those with high flexibility (Moseley et al., 2003). The results of our investigation were in good agreement with the above observation. The resemblance of ankle angular motion in the tightness group might be attributable to the compensatory motions occurring in the knee and hip joints. The knee and hip joints have been documented to remain more flexed throughout stance phase in the subjects with an equinus gait (Baddar et al., 2002; Armand et al., 2006; Matjacic´ et al., 2006). Our results showed the there was a comparable tendency toward the greater knee and hip flexion around midstance phase, and the knee and hip flexion angles further increased in the tightness group at the time of maximal ankle dorsiflexion. A normal gait requires tibial advancement over the foot during stance phase, which contributes to forward movement of the body. Considering the maximal range of ankle dorsiflexion during gait, both groups in our study had ranges which were consistent with the reported ranges (10–15°) in the studies (Barr and Backus, 2001; Smith et al., 1996). Gastrocnemius was a two-joint muscle crossing ankle and knee joints and the longest gastrocnemius length was in the midstance period (Orendurff et al., 2005). The tightness of gastrocnemius could affect the joint angles in the ankle, knee, or both joint. Baddar et al. (2002) and Matjacic´ et al. (2006) had reported that severe gastrocnemius contracture both decreased maximal ankle dorsiflexion and knee extension during stance phase. Our re-

sults implied that the increased hip and knee flexion angles during midstance might be a compensatory gait pattern in response to the gastrocnemius tightness. The increase in knee flexion could be the direct effect of gastrocnemius tightness due to the passive length– tension properties of the two-joint muscle. Moseley et al. (2003) also demonstrated that the subjects with low gastrocnemius flexibility had a similar ankle kinematical pattern to those who with high flexibility, but they did not investigate the patterns of knee kinematics. Though there was no difference of ankle joint at the time of max ankle dorsiflexion between groups in our experiment, the effect of gastrocnemius tightness could be detected through the knee joint kinematics. The compensatory increased knee flexion (4–5° relative to the control group) could be the result of gastrocnemius tightness. The hip adaptation might be associated with the increased knee flexion to retain the appropriate muscle length of quadriceps and provide suitable stride length during gait cycle. Baddar et al. proposed that during the stance phase, there was a negative correlation (r = 0.7) between ankle and knee motions in the normal subjects whereas there was a positive correlation (r = 0.7) in the subjects with equinus gait. The positive correlation of the ankle dorsiflexion and knee flexion could signify the coupling motion between these two joints resulted from gastrocnemius shortening (Baddar et al., 2002). Motion couplings between the ankle and knee joints for tightness and control groups were further analyzed in the present study. Our analysis revealed that the control group resembled the high negative correlation between ankle and knee motion at the both cadences. The tightness group had a less negative correlation between knee and ankle motion at the both cadences. The negative correlation in the tightness group might infer that the effect of gastrocnemius tightness on coupling motion in the present study was not as severe as that in the subjects with equinus gait. 4.2. Joint work The ankle power trajectories in the subjects with equinus gait or gastrocnemius contracture emulation were reported to show the

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greater work absorption during early stance phase compared to the normal gait pattern (Baddar et al., 2002; Armand et al., 2006; Matjacic´ et al., 2006). Though our subjects with gastrocnemius tightness demonstrated the similar power curves of ankle joint with those of the control group, they tended to have the greater ankle work absorption during the stance phase. The ankle work absorption reflected the plantar flexors performing the eccentric contractions to control the tibial advancement over the foot during stance phase (Proske et al., 2004). The insufficient flexibility exacerbated the muscular demands during the eccentric muscle contractions and was one of the major factors contributing to muscle strains (Hertling and Kessler, 2006). Therefore, the greater ankle work absorption in gastrocnemius tightness group predisposed the plantar flexors to strain injuries especially at the faster cadence. The knee and hip power trajectories in subjects with equinus gait or simulated gastrocnemius contracture have been documented to be similar to those of normal subjects (Armand et al., 2006; Matjacic´ et al., 2006). Our study also demonstrated a similarity between tightness and control groups in the knee and hip power patterns. The knee joint extended almost fully during the midstance phase, and the quadriceps contracted to generate work for supporting body while the contralateral limb was engaged in swing. Unlike the greater knee work generation observed in the previous studies (Baddar et al., 2002; Armand et al., 2006; Matjacic´ et al., 2006), our tightness group showed the decreased knee work generation during stance phase. One possible explanation for this discrepancy might be that the gastrocnemius tightness increased the knee flexion angle, unlocking knee joint, during midstance phase. Rose and Gamble also proposed that work generation and absorption at knee joints could be characterized as a control process in normal walking (Rose and Gamble, 1994). The scenario of the unlocking knee might render the inadequate control of knee joint and the reduction in work generation. Studies on urban pedestrians indicated that the medium range of cadences for adults was around 100–120 steps/min (Inman et al., 1981). The beeps of the metronome in the present study were preset at 100 steps/min for the regular cadence and at 140 steps/min for the faster cadence. The preset cadence has usually been applied to control the walking velocity for research purposes and could influence the joint work of lower extremities (Chen et al., 1997; Teixeira-Salmela et al., 2008; Graf et al., 2005). Teixeira-Salmela et al. (2008) had reported that true step cadence at the natural cadence was similar to those at 120 steps/min controlled by a metronome. The energy generation and absorption for each joint in lower extremity were not different between the natural cadence and controlled cadence by a metronome. The self-selected normal and fast walking speeds were also tested in our preliminary experiment. The average cadences were around 92–107 steps/min for the normal walking and 126–148 steps/min for fast walking. Barr and Backus (2001) proposed that the larger variations in step cadence, 90–140 steps/min, for walking at selfselected walking speed. The similar finding of variation in the actual step cadence with self-selected walking speed was observed in our preliminary experiment. Therefore, we considered that the self-selected walking speed might influence the effect of gastrocnemius tightness on gait pattern. In order to study the cadence effect on joint angle and joint work of lower extremity during gait, a metronome was applied to decrease the variation of the self-selected walking speed. The subjects would practice walking several times to habituate the preset cadence before the experiments, so the alteration of natural gait patterns by the preset cadence might be minimized. Our results were in coincidence with the previously published findings that a faster preset cadence was correlated with the greater work generation for all joints. It is believed that the faster cadence increases the work generation by accelerating the body segments with the concentric muscle contractions.

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Our findings demonstrating the greater knee and lesser ankle work absorption at the faster cadence were in agreement with those of earlier investigations (Chen et al., 1997; Teixeira-Salmela et al., 2008; Graf et al., 2005). Teixeira-Salmela et al. suggested that the increased work absorption which was observed at the knee joint, the energy modulator, might be due to the work of numerous two-joint muscles in promoting energy flow between segments and transferring energy to optimize energy consumption at the faster cadences (Teixeira-Salmela et al., 2008). The present findings supported the evidence in favor of an alternating role in work absorption between the knee and ankle joints at different cadences. Though the ankle work absorption decreased companied with the increased knee absorption at the faster cadence, the tightness group still had the greater ankle work absorption compared to the controls. The tight gastrocnemius muscle might be strained by the vigorous motion from the eccentric gastrocnemius contractions, if the work shift between ankle and knee failed to occur. A limitation of this study was the biomechanical considerations for the major joints of the lower extremities mainly in the sagittal plane. A shortened Achilles tendon may cause the abnormal pronation of the hind foot with respect to the forefoot for the compensation of insufficient ankle dorsiflexion. Further kinematic researches might be necessary to analyze the lower extremities in different motion planes to reveal more complicated compensatory strategies for the inflexibility of gastrocnemius muscle. The neurological and physiological changes with aging were found to be: increase in reaction time, decrease in acuity of vestibular, visual, and somatosensory systems, general decrease in muscle strength, more energy consumption, and loss of passive range of motion in the joint. It has been reported that the older adults have decreased walking velocity and subtle changes at the amplitude level in joint and power profiles (Prince et al., 1997; Kerrigan et al., 1997). Due to the relatively young study group at the present study, we concerned our findings might not be suitable for generalizing the conclusions for the older adults. Though a recent study found no age-related differences in lengthening of the gastrocnemius lateralis muscle tendon complex during stance, both the physical changes associated with aging process and gastrocnemius tightness would result in the subtle gait alterations in the older adults (Mian et al., 2007). The effect of gastrocnemius tightness on the gait pattern of the older adults warrants further investigation.

5. Conclusions Subjects with gastrocnemius tightness significantly decreased the work generation at knee, and increased the work absorption at ankle joint. The potential disturbance of the knee control and the strain injuries of gastrocnemius muscle might be crucial in the clinical considerations for the subjects with gastrocnemius tightness.

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