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Muscle activation during fast walking with two types of foot orthoses in participants with cavus feet
Journal of Electromyography and Kinesiology 43 (2018) 7–13
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Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin
Muscle activation during fast walking with two types of foot orthoses in participants with cavus feet
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Gabriel Moisana,b,c, , Martin Descarreauxb,c, Vincent Cantinb,c a
Département d’anatomie, Université du Québec à Trois-Rivières, 3351 Boul Des Forges, Trois-Rivières, Quebec G9A 5H7, Canada Département des sciences de l’activité physique, Université du Québec à Trois-Rivières, 3351 Boul Des Forges, Trois-Rivières, Quebec G9A 5H7, Canada c Groupe de recherche sur les affections neuro-musculo-squelettiques (GRAN), Université du Québec à Trois-Rivières, 3351 Boul Des Forges, Trois-Rivières, Quebec G9A 5H7, Canada b
A R T I C LE I N FO
A B S T R A C T
Keywords: Foot orthoses Foot orthoses with a lateral bar Electromyography Walking
The aim of this study was to quantify the effects of foot orthoses (FOs) with and without a lateral bar on muscle activity of participants with cavus feet. Fifteen participants were recruited from the Université du Québec à Trois-Rivières students and podiatry clinic. The muscle activity of the tibialis anterior, fibularis longus, gastrocnemius lateralis and medialis, vastus medialis and lateralis, biceps femoris and gluteus medius were recorded during fast walking under two experimental conditions (FOs with and without a lateral bar) and a control condition (shoes). Experimentations were completed after a one-month adaptation period to each experimental condition. The root mean square of the electromyography (EMG) data was analyzed. To compare the effects between conditions, a curve analysis was performed using one-dimensional statistical parametric mapping. The main result of this study was an increased gastrocnemius lateralis muscle activity (maximum mean difference: +28%) during the propulsion phase of gait (44–46%) when participants wore FOs compared to the control condition. This result will help researchers and clinicians better understand the FOs’ EMG effects of individuals with cavus feet. As FOs are mainly prescribed for symptomatic patients, future studies should assess their effects on individuals suffering of a pathology, such as Achilles tendinopathy.
1. Introduction Foot orthoses (FOs) are often used to manage, with an overall good efficacy, numerous musculoskeletal pathologies such as posterior tibial tendon dysfunction (Kulig et al., 2009), patellofemoral pain syndrome (Munuera and Mazoteras-Pardo, 2011) and medial tibial stress syndrome (Loudon and Dolphino, 2010). Their effects on muscle activity could perhaps explain their efficacy as numerous studies have demonstrated that they affect muscle activity during walking (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley et al., 2010a). It has also been shown that, by adding modifications to FOs, it is possible to modulate muscle activity (Moisan and Cantin, 2016, Mundermann et al., 2006) during locomotion. FOs modifications can be described as any material you remove or add to the orthoses to increase their specificity. One of these modifications is a lateral bar. This modification was described by Moisan and Cantin (2016) as a one-centimeter wide ethylene-vinylacetate (EVA) bar glued under the lateral part of the FOs lying from the extrinsic rearfoot post to the distal end of the shell. The utilization of the lateral bar is based on the subtalar axis location rotational
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equilibrium (SALRE) theory (Kirby, 2001) according to which any force acting laterally to the ankle and subtalar joint axes will produce a pronatory moment around these joints. Consequently, the addition of a lateral bar should decrease pronatory muscles activity. In fact, it has been observed that FOs with a lateral bar decrease the fibularis longus muscle activity during walking (Moisan and Cantin, 2016). In clinical contexts, lateral bars are used to treat patients with pain or discomfort associated with excessive rearfoot supination moments during gait or injuries to lateral ligaments and muscles of the ankle and leg, such as chronic ankle instability and fibular tendinopathy. However, the effects of this modification have never been studied in individuals with cavus feet. These individuals present increased peak pressures under the rearfoot and pressure–time integrals under the rearfoot and forefoot (Burns et al., 2005), less peak ankle eversion (Powell et al., 2011) and more lateral ground reaction forces (Hillstrom et al., 2013) compared to individuals with flatter feet during walking. The differences in muscle activity between individuals with cavus feet compared to those with flatter feet are still poorly documented. However, according to the SALRE theory (Kirby, 2001), it can be hypothesized that individuals
Corresponding author. E-mail addresses: [email protected] (G. Moisan), [email protected] (M. Descarreaux), [email protected] (V. Cantin).
https://doi.org/10.1016/j.jelekin.2018.08.002 Received 28 March 2018; Received in revised form 10 July 2018; Accepted 14 August 2018 1050-6411/ © 2018 Elsevier Ltd. All rights reserved.
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Fig. 1. Muscle activity with shoes and FOs.
mean activity (Moisan and Cantin, 2016, Murley et al., 2010a, Telfer et al., 2013a, Tomaro and Burdett, 1993). It has been previously found that performing these zero-dimensional analyses (timing, peak or mean activity) produce a high rate of false positive results (Pataky et al., 2016). A false positive is observed when an effect is inferred but in fact, none exists. The convention in most biomechanics studies is to set α at 0.05, which implies that one accepts a 5% false positive rate when conducting the hypothesis testing. However, Pataky et al. (2016) found that for biomechanical data (EMG, kinematics and kinetics), the median false positive rate was 0.382 and was as high as 0.764 for variables with a three-dimensional vector (e.g. joint angles during gait). The high false positive rate could be explained by the fact that hypotheses pertaining to one-dimensional data are tested using a traditional zero-dimensional Gaussian model of randomness, but variance in these datasets is unidimensional. To avoid this problem, it has been suggested to use unidimensional procedures, such as one-dimensional statistical parametric mapping (SPM) (Pataky, 2012, Pataky et al., 2016). The main objective of this study was to quantify the effects of FOs with and without lateral bar on muscle activity of participants with cavus feet. It was hypothesized that FOs will decrease pronator muscles activity and increase supinator muscles activity.
with cavus feet present a laterally deviated subtalar joint axis. This deviation could decrease the level arm of the pronator muscles and therefore increase the activity of these muscles. Previous studies assessing the effects of FOs on muscle activity during walking used a self-selected (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley and Bird, 2006, Murley et al., 2010a, Telfer et al., 2013a) or a predetermined speed (Tomaro and Burdett, 1993). It has been demonstrated that muscle activity of the lower limb increases at faster walking speeds (Chiu and Wang, 2007, Den Otter et al., 2004, Murley et al., 2014). However, FOs’ effects at a fast walking pace have not been quantified. It is then unknown if FOs have similar effects on muscle activity when walking at a faster pace. Therefore, there is a need to assess the effects of FOs on muscle activity at a fast walking speed, as it could have clinically important implications. It will help better understanding the underlying mechanisms explaining the FOs’ therapeutic efficacy. The FOs’ effects on muscle activity are regularly studied in the literature, but according to Pataky et al. (2016), the analyses used in the previously published studies could be problematic. Indeed, by having a time component, muscle activity data are considered one-dimensional. However, in most previous studies assessing the effects of FOs on muscle activity, electromyography (EMG) data were analyzed with variables that are a zero-dimensional representation (punctual representation), such as timing (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley and Bird, 2006, Murley et al., 2010a), peak activity (Murley and Bird, 2006, Murley et al., 2010a, Telfer et al., 2013a) and 8
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Fig. 1. (continued)
2. Methods and materials
described by Root et al. (1971). Positive casts were then produced and the FOs’ shells were molded on them. The orthotist technician removed all gross abnormalities on the positive casts but no other modification was performed. During the experiments, the FOs were worn by each participant in the same shoe model (Athletic Works, Model: Rupert), but in their proper shoe size.
2.1. Participants In this study, 15 participants, nine men and six women (age: 27.7 ± 9.0 yr, height 174.9 ± 10.9 cm, weight 74.5 ± 17.7 kg, Foot Posture Index score: −4.3 ± 2.3), with no history of macrovascular symptoms, neuromuscular diseases or traumatic injuries affecting their ability to walk six months prior to the experimentations were recruited. No participants had worn FOs on a regular basis for at least 6 months prior to the study. Their ≪Foot Posture Index≫ (Redmond et al., 2006) score had to be −2 or less (Crosbie and Burns, 2008). All participants provided a written informed consent prior to their enrolment in the study. The experimental protocol was approved by the Université du Québec à Trois-Rivières (UQTR) (Canada) Ethics Committee. Potential participants were recruited among the UQTR students and from the UQTR outpatient podiatry clinic between April 1st and July 1st 2016.
2.3. Instrumentation Walking speed was recorded with electronic photocells timing gates (Brower Timing System, USA). EMG data were collected using the Delsys EMGworks(®) software. Muscle activity of the gluteus medius, vastus lateralis, vastus medialis, biceps femoris, gastrocnemius medialis, gastrocnemius lateralis, fibularis longus and tibialis anterior were recorded with a wireless surface EMG system (Delsys Trigno, Boston, USA). The muscles chosen are commonly assessed in gait analysis studies with and without FOs (Murley et al., 2009) and represent muscle groups that are greatly solicited during walking. Skin impedance was reduced by shaving, abrading with fine-grade sandpaper and wiping with alcohol swabs. The EMG electrodes positioning was carried out according to the SENIAM recommendations (Hermens et al., 2000). The electrodes (27 mm × 37 mm × 15 mm) were 99% silver contact material with a four-bar formation. The distance between the electrodes was 10 mm. Data were sampled at 1.93 kHz. The gain was 1000; the maximum intraelectrode impedance was 6 kOhm; common noise removal ratio (CNRR) of the EMG amplifier was > 80 dB and a 16 bits A/D
2.2. Foot orthoses The FOs used in this study were fabricated by a certified orthotist technician and were made of a 3.2 mm thick polypropylene shell. These ¾ length FOs had an EVA straight extrinsic rearfoot post, cut at 75% of the length of the heel cup. All FOs had an EVA lateral bar that could easily be removed with a heat gun when needed. FOs were made from plaster casts taken with the subtalar joint held in neutral position, as 9
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Fig. 2. Muscle activity with shoes and FOs with a lateral bar.
lateral bar) one hour the first day, and one hour more each following days until the participant could wear them all day. This protocol is commonly used in clinical practice to reduce pain and discomfort experienced by patients during the first days of wearing orthoses. Then, participants had to wear the assigned orthoses in their everyday activities for one month. Everyday, participants completed a logbook in which they had to quantify the level of pain felt when wearing the orthoses on a visual analog scale ranging from 0 to 10 and to report the number of hours they were worn. After the adaptation period, participants attended their first experimental session at UQTR’s gait analysis laboratory. The experimental protocol consisted of walking on a 10 m walkway with and without the assigned orthoses as fast as they could, without running. Participants were first asked to perform five familiarization trials. During these trials, walking speed was recorded with photocells timing gates positioned at 2.5 and 7.5 m on the walkway and was averaged for each participant. Then, five trials were completed in the assigned orthoses and finally five trials in the control condition (shoes only). All trials with walking speed varying from ± 5% of the mean speed established during the familiarization trials were rejected and immediately repeated. A 5-min break was given to the participants between the FOs’ and the control trials. After the first testing session, the experimental conditions were interchanged for all participants: a lateral bar was added to the FOs and was removed from the FOs with a lateral bar. All participants had to wear the new orthoses in their everyday activities for the next month and subsequently completed the second testing
converter was used. The EMG data were filtered with a zero phase lag, bi-directional, 20–450 Hz bandpass fourth-order Butterworth filter and full-wave rectified. Analyses were performed on the EMG data root mean square (RMS), calculated with a moving window of 50 ms width with an overlap of 25 ms and were visually inspected for movement artifact or crosstalk. RMS data were normalized with the mean peak RMS of all trials of the control condition for each testing session. To determine the initial contact of the foot, an accelerometer (Delsys Trigno, Boston, USA) was positioned on the tibial tuberosity of the participant’s tested leg. The initial contact was defined as the peak amplitude of the accelerometer curve as described by Mizrahi et al. (2000). The accelerometer’s sampling rate was 148.15 Hz. All measurements were recorded on the leg of the participant that presented the lowest FPI score. If no differences were observed between both feet, the dominant leg (Moisan and Cantin, 2016) was chosen. Three strides by trial were used for the analyses, for a total of 15 strides evaluated for each condition for each speed. 2.4. Protocol Approximately two weeks after the plaster casts were made, the experimental conditions were dispensed to the participants. Seven participants were randomly asked to wear FOs and eight participants were asked to wear FOs with a lateral bar. One of the researchers (GM) confirmed the FOs’ conformity and explained the progressive adaptation protocol consisting of wearing the assigned FOs (with or without a 10
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Fig. 2. (continued)
session during which the same protocol was performed. They had to fill the same logbook to quantify the pain felt when wearing the orthoses and the number of hours they were worn.
No comparison between FOs and FOs with a lateral bar was performed as it has been shown that between-session absolute reliability of EMG data was poor (Moisan and Cantin, 2016, Murley et al., 2010b).
2.5. Analysis
3. Results
The Shapiro-Wilk test value was used to assess normality of descriptive data. As they were not normally distributed, Wilcoxon tests were performed with a level of statistical significance set at p ≤ 0.05 to compare the descriptive data between groups. The D’Agostino-Pearson test was used to evaluate the distribution of EMG data. To compare the effects of experimental conditions on muscle activity between the two conditions, a curve analysis was performed using SPM (Friston, 2007, Pataky, 2012). Each individual stride was normalized to 100% according to its duration. To compare the differences between each normalized point of the curves, the non-parametric permutation method test (SnPM) (Nichols and Holmes, 2002, Pataky et al., 2015) was used. The SnPM threshold above which only α = 5% of the data would be expected, had the test statistic trajectory resulted from an equivalently smooth random process, was calculated. The individual probability that each supra-threshold cluster could have resulted from an equivalently smooth random process was determined. Cohen’s d effect sizes and maximum mean differences (MD) were calculated when statistically significant differences were observed. All EMG analyses (D’AgostinoPearson and permutation tests) were implemented using the open access SPM1D code (www.spm1d.org) in Python software (Version 2.7).
No difference was found in the average time the experimental conditions were worn per day during the one-month adaptation periods between testing sessions (FOs: 6.54 ± 1.78 h, FOs with a lateral bar: 5.94 ± 1.85 h, p = 0.14) and in level of pain felt on a 0 to 10 scale when wearing the experimental conditions (FOs: 0.79 ± 1.24, FOs with a lateral bar: 0.93 ± 1.25, p = 0.92). No difference in walking speed was found for FOs (FOs: 2.55 ± 0.56 vs control 2.53 ± 0.54 m/ s, p = 0.39) and FOs with a lateral bar (FOs with a lateral bar: 2.52 ± 0.51 vs control: 2.52 ± 0.48 m/s, p = 0.43) compared to the control condition. For the tibialis anterior muscle, results for the FOs with a lateral bar of one participant had to be excluded from the analyses due to high levels of artifact caused by excessive perspiration. For both experimental conditions, the activity of all muscles was similar compared to the control condition (see Figs. 1 and 2). However, one supra-threshold cluster (44–46%) exceeded the critical threshold of 15.29 as the activity of the gastrocnemius lateralis muscle was significantly increased with FOs (Fig. 1e). The precise probability that a supra-threshold cluster of this size would be observed in repeated random samplings was p < 0.01, the Cohen’s d effect size was 0.32 and MD was + 28% (at 45% of the gait cycle). One supra-threshold cluster 11
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the SALRE theory (Kirby, 2001). Participants with cavus feet present less peak ankle eversion (Powell et al., 2011) and more lateral ground reaction forces (Hillstrom et al., 2013) compared to population with flatter feet during walking. It can be hypothesized that the medial longitudinal arch of the 3.2 mm polypropylene FOs’ shell could counterbalance the effects of the lateral bar for this population that already has a more inverted gait pattern. Future studies should consider using a thinner and more flexible FOs’ shell or add a valgus wedge as it has been shown that it increases external ankle eversion moment (Telfer et al., 2013b). Researchers should also consider assessing other biomechanical parameters such as kinematics and kinetics to better interpret the EMG differences and better understand the underlying FOs mechanism of action. Also, the absence of results for muscles such as fibularis longus, tibialis anterior and gastrocnemius medialis compared to previous studies that found significant differences when wearing FOs (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley and Bird, 2006, Murley et al., 2010a) could perhaps be explained by the analyses performed. As mentioned previously, most studies that assessed the effects of FOs on muscle activity used a traditional zero-dimensional approach to analyze one-dimensional datasets. This implies that the results have a high risk of having yielded statistical significance when, in fact, they were only false positive results. The results of previous studies are not entirely invalidated because large effects, when present, can generally be observed irrespective of the analysis procedure (Pataky et al., 2016). However, smaller effects should be interpreted with caution. Further studies using a unidimensional approaches are needed to confirm or infirm the results of the previous studies. The difference between studies could also be explained by the heterogeneity between the recruited participants. A number of limitations should be taken into account. First, only asymptomatic participants were recruited for this study whereas FOs are mainly prescribed for patients with musculoskeletal pathologies. These results should be extrapolated with caution to a symptomatic population. Second, during the one-month period of wear before each testing session, the participants wore the experimental conditions in their own shoes. By using standardized shoes during the experimental protocol, it was possible to control confounding variables. However, it may not have been representative of their everyday shoes. Third, the fast walking speed chosen in this study limits the external validity of the results. The mean walking speed of the participants of this study may not be reachable for males over 50 years old and females over 40 years old (Bohannon, 1997) or for symptomatic individuals.
(77–78%) also exceeded the critical threshold of 15.62 as the activity of the tibialis anterior muscle was significantly decreased with FOs with a lateral bar with p = 0.01, d = 0.27 and MD was −15% (at 78% of the gait cycle) (see Fig. 2h). 4. Discussion The main objective of this study was to quantify the effects of FOs with and without a lateral bar on muscle activity of participants with cavus feet. When assessing the effects of FOs on muscle activity compared to a control condition, an increased gastrocnemius lateralis activity from 44 to 46% of the walking cycle with a MD of +28% was observed. This significant difference occurred in the peak amplitude region during the beginning of the propulsion phase of walking. It has been shown that peak gastrocnemius lateralis muscle activity occurs around 40 to 45% of the walking cycle, which corresponds to the time the heel lifts from the ground (Clancy et al., 2004). When visually comparing the curves with and without FOs for this muscle (see Fig. 1), one can note that they separate from each other through a significant portion (37–51%) of the gait cycle. Even if the differences are not statistically significant throughout this period, such differences could be of clinical significance. However, it is still unknown how much changes (increase or decrease) in muscle activity is needed to produce a clinical impact. Future studies should include EMG assessments and pain evaluation with a longitudinal experimental protocol to try to determine the minimal clinically significant EMG differences for symptomatic individuals. As mentioned earlier, participants with cavus feet have less peak ankle eversion (Powell et al., 2011) and more lateral ground reaction forces (Hillstrom et al., 2013). According to the SALRE theory (Kirby, 2001), it can be hypothesized that the medial longitudinal arch of the FOs creates an inversion moment around the subtalar and ankle joints axes during the end of the midstance and the beginning of the propulsive phases of gait. For these individuals that already have a more inverted gait pattern, the gastrocnemius lateralis muscle might compensate this increased load by increasing its activity. One can hypothesize that adding a lateral bar to the FOs creates a pronatory moment around these joints and therefore cancelling the effects of the medial longitudinal arch, explaining the absence of EMG differences when comparing FOs with a lateral bar to the shod condition. This result is not consistent with previous studies that quantified the effects of FOs on peak gastrocnemius lateralis muscle activity, in which no difference (Telfer et al., 2013a) and a decreased activity (Moisan and Cantin, 2016) was observed. The heterogeneity of participants’ foot type, walking speed and FOs used could perhaps explain the variability of results across studies. However, the results of this study are novative as the effects of FOs on muscle activity of participants with cavus feet during fast walking have never been previously studied. When comparing FOs with a lateral bar and the control condition effects on muscle activity, a decreased tibialis anterior activity from 77 to 78% of the walking cycle was observed. The effects of different types of FOs on the activity of the tibialis anterior muscle are inconsistent in previous studies. Indeed, no difference (Murley et al., 2010a, Telfer et al., 2013a), a decreased activity (Dedieu et al., 2013, Moisan and Cantin, 2016) and an increased activity (Tomaro and Burdett, 1993) were previously observed. However, only one study assessed FOs with a lateral bar and found no difference during the stance phase of walking (Moisan and Cantin, 2016). Considering the very short period of time the supra-threshold cluster exceeded the critical threshold and the small Cohen’s d effect size, this result should be interpreted with caution. Based on earlier published data, we hypothesized that the activity of the fibularis longus muscle would be decreased with FOs with a lateral bar (Moisan and Cantin, 2016). The lack of significant differences could perhaps be explained by the type of FOs used. As previously mentioned, the clinical goal of adding the lateral bar to the FOs is to increase the pronatory moments across the ankle and subtalar joints according to
5. Conclusion This study suggests that FOs with a lateral bar have very limited effects on lower limb muscle activity of participants with cavus feet during fast walking. The study also suggests that the gastrocnemius lateralis muscle activity is increased with FOs in the early stages of the propulsion phase during fast walking. This result will help researchers and clinicians better understand the effects of different FO types on muscle activity of individuals with cavus feet.
Conflict of interest The authors declare that they have no conflict of interest relating to the material presented in this article.
Acknowledgements This study was funded by the Canadian Institutes of Health Research (CIHR) and the Fonds de Recherche du Québec-Santé (FRQS) through scholarships received by the first author. 12
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Appendix A. Supplementary matreial
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Gabriel Moisan received his M.Sc. in kinesiology at ‘‘Université du Québec à Trois-Rivières ” (UQTR), Canada, in 2015, where he is currently pursuing a doctoral degree in biomedical sciences. He is also involved in research conducted by the ‘‘Groupe de Recherche surles Affections Neuro-musculo-squelettiques’’ (GRAN). His primary research interests are locomotion, foot and ankle biomechanics and foot orthoses.
Martin Descarreaux received his Ph.D. from ‘‘Université Laval’’, Canada, in 2004. He is a Full Professor at ‘‘Université du Québec à Trois-Rivières’’ (UQTR)’’, Canada, in the department of Human Kinetics. He is the director of the ‘‘Groupe de Recherche sur les Affections Neuro-musculo-squelettiques’’ (GRAN). His main research interests are motor control and proprioceptive deficits associated with chronic and recurrent low back pain.
Vincent Cantin received his Ph.D. from ‘‘Université Laval’’, Canada, in 2009. He is a Full Professor at ‘‘Université du Québec à Trois-Rivières’’ (UQTR), Canada, in the department of Human Kinetics and an active member of the ‘‘Groupe de Recherche sur les Affections Neuromusculosquelettiques’’ (GRAN). His primary research interests are locomotion and foot biomechanics.
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Journal of Electromyography and Kinesiology journal homepage: www.elsevier.com/locate/jelekin
Muscle activation during fast walking with two types of foot orthoses in participants with cavus feet
T
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Gabriel Moisana,b,c, , Martin Descarreauxb,c, Vincent Cantinb,c a
Département d’anatomie, Université du Québec à Trois-Rivières, 3351 Boul Des Forges, Trois-Rivières, Quebec G9A 5H7, Canada Département des sciences de l’activité physique, Université du Québec à Trois-Rivières, 3351 Boul Des Forges, Trois-Rivières, Quebec G9A 5H7, Canada c Groupe de recherche sur les affections neuro-musculo-squelettiques (GRAN), Université du Québec à Trois-Rivières, 3351 Boul Des Forges, Trois-Rivières, Quebec G9A 5H7, Canada b
A R T I C LE I N FO
A B S T R A C T
Keywords: Foot orthoses Foot orthoses with a lateral bar Electromyography Walking
The aim of this study was to quantify the effects of foot orthoses (FOs) with and without a lateral bar on muscle activity of participants with cavus feet. Fifteen participants were recruited from the Université du Québec à Trois-Rivières students and podiatry clinic. The muscle activity of the tibialis anterior, fibularis longus, gastrocnemius lateralis and medialis, vastus medialis and lateralis, biceps femoris and gluteus medius were recorded during fast walking under two experimental conditions (FOs with and without a lateral bar) and a control condition (shoes). Experimentations were completed after a one-month adaptation period to each experimental condition. The root mean square of the electromyography (EMG) data was analyzed. To compare the effects between conditions, a curve analysis was performed using one-dimensional statistical parametric mapping. The main result of this study was an increased gastrocnemius lateralis muscle activity (maximum mean difference: +28%) during the propulsion phase of gait (44–46%) when participants wore FOs compared to the control condition. This result will help researchers and clinicians better understand the FOs’ EMG effects of individuals with cavus feet. As FOs are mainly prescribed for symptomatic patients, future studies should assess their effects on individuals suffering of a pathology, such as Achilles tendinopathy.
1. Introduction Foot orthoses (FOs) are often used to manage, with an overall good efficacy, numerous musculoskeletal pathologies such as posterior tibial tendon dysfunction (Kulig et al., 2009), patellofemoral pain syndrome (Munuera and Mazoteras-Pardo, 2011) and medial tibial stress syndrome (Loudon and Dolphino, 2010). Their effects on muscle activity could perhaps explain their efficacy as numerous studies have demonstrated that they affect muscle activity during walking (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley et al., 2010a). It has also been shown that, by adding modifications to FOs, it is possible to modulate muscle activity (Moisan and Cantin, 2016, Mundermann et al., 2006) during locomotion. FOs modifications can be described as any material you remove or add to the orthoses to increase their specificity. One of these modifications is a lateral bar. This modification was described by Moisan and Cantin (2016) as a one-centimeter wide ethylene-vinylacetate (EVA) bar glued under the lateral part of the FOs lying from the extrinsic rearfoot post to the distal end of the shell. The utilization of the lateral bar is based on the subtalar axis location rotational
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equilibrium (SALRE) theory (Kirby, 2001) according to which any force acting laterally to the ankle and subtalar joint axes will produce a pronatory moment around these joints. Consequently, the addition of a lateral bar should decrease pronatory muscles activity. In fact, it has been observed that FOs with a lateral bar decrease the fibularis longus muscle activity during walking (Moisan and Cantin, 2016). In clinical contexts, lateral bars are used to treat patients with pain or discomfort associated with excessive rearfoot supination moments during gait or injuries to lateral ligaments and muscles of the ankle and leg, such as chronic ankle instability and fibular tendinopathy. However, the effects of this modification have never been studied in individuals with cavus feet. These individuals present increased peak pressures under the rearfoot and pressure–time integrals under the rearfoot and forefoot (Burns et al., 2005), less peak ankle eversion (Powell et al., 2011) and more lateral ground reaction forces (Hillstrom et al., 2013) compared to individuals with flatter feet during walking. The differences in muscle activity between individuals with cavus feet compared to those with flatter feet are still poorly documented. However, according to the SALRE theory (Kirby, 2001), it can be hypothesized that individuals
Corresponding author. E-mail addresses: [email protected] (G. Moisan), [email protected] (M. Descarreaux), [email protected] (V. Cantin).
https://doi.org/10.1016/j.jelekin.2018.08.002 Received 28 March 2018; Received in revised form 10 July 2018; Accepted 14 August 2018 1050-6411/ © 2018 Elsevier Ltd. All rights reserved.
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Fig. 1. Muscle activity with shoes and FOs.
mean activity (Moisan and Cantin, 2016, Murley et al., 2010a, Telfer et al., 2013a, Tomaro and Burdett, 1993). It has been previously found that performing these zero-dimensional analyses (timing, peak or mean activity) produce a high rate of false positive results (Pataky et al., 2016). A false positive is observed when an effect is inferred but in fact, none exists. The convention in most biomechanics studies is to set α at 0.05, which implies that one accepts a 5% false positive rate when conducting the hypothesis testing. However, Pataky et al. (2016) found that for biomechanical data (EMG, kinematics and kinetics), the median false positive rate was 0.382 and was as high as 0.764 for variables with a three-dimensional vector (e.g. joint angles during gait). The high false positive rate could be explained by the fact that hypotheses pertaining to one-dimensional data are tested using a traditional zero-dimensional Gaussian model of randomness, but variance in these datasets is unidimensional. To avoid this problem, it has been suggested to use unidimensional procedures, such as one-dimensional statistical parametric mapping (SPM) (Pataky, 2012, Pataky et al., 2016). The main objective of this study was to quantify the effects of FOs with and without lateral bar on muscle activity of participants with cavus feet. It was hypothesized that FOs will decrease pronator muscles activity and increase supinator muscles activity.
with cavus feet present a laterally deviated subtalar joint axis. This deviation could decrease the level arm of the pronator muscles and therefore increase the activity of these muscles. Previous studies assessing the effects of FOs on muscle activity during walking used a self-selected (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley and Bird, 2006, Murley et al., 2010a, Telfer et al., 2013a) or a predetermined speed (Tomaro and Burdett, 1993). It has been demonstrated that muscle activity of the lower limb increases at faster walking speeds (Chiu and Wang, 2007, Den Otter et al., 2004, Murley et al., 2014). However, FOs’ effects at a fast walking pace have not been quantified. It is then unknown if FOs have similar effects on muscle activity when walking at a faster pace. Therefore, there is a need to assess the effects of FOs on muscle activity at a fast walking speed, as it could have clinically important implications. It will help better understanding the underlying mechanisms explaining the FOs’ therapeutic efficacy. The FOs’ effects on muscle activity are regularly studied in the literature, but according to Pataky et al. (2016), the analyses used in the previously published studies could be problematic. Indeed, by having a time component, muscle activity data are considered one-dimensional. However, in most previous studies assessing the effects of FOs on muscle activity, electromyography (EMG) data were analyzed with variables that are a zero-dimensional representation (punctual representation), such as timing (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley and Bird, 2006, Murley et al., 2010a), peak activity (Murley and Bird, 2006, Murley et al., 2010a, Telfer et al., 2013a) and 8
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Fig. 1. (continued)
2. Methods and materials
described by Root et al. (1971). Positive casts were then produced and the FOs’ shells were molded on them. The orthotist technician removed all gross abnormalities on the positive casts but no other modification was performed. During the experiments, the FOs were worn by each participant in the same shoe model (Athletic Works, Model: Rupert), but in their proper shoe size.
2.1. Participants In this study, 15 participants, nine men and six women (age: 27.7 ± 9.0 yr, height 174.9 ± 10.9 cm, weight 74.5 ± 17.7 kg, Foot Posture Index score: −4.3 ± 2.3), with no history of macrovascular symptoms, neuromuscular diseases or traumatic injuries affecting their ability to walk six months prior to the experimentations were recruited. No participants had worn FOs on a regular basis for at least 6 months prior to the study. Their ≪Foot Posture Index≫ (Redmond et al., 2006) score had to be −2 or less (Crosbie and Burns, 2008). All participants provided a written informed consent prior to their enrolment in the study. The experimental protocol was approved by the Université du Québec à Trois-Rivières (UQTR) (Canada) Ethics Committee. Potential participants were recruited among the UQTR students and from the UQTR outpatient podiatry clinic between April 1st and July 1st 2016.
2.3. Instrumentation Walking speed was recorded with electronic photocells timing gates (Brower Timing System, USA). EMG data were collected using the Delsys EMGworks(®) software. Muscle activity of the gluteus medius, vastus lateralis, vastus medialis, biceps femoris, gastrocnemius medialis, gastrocnemius lateralis, fibularis longus and tibialis anterior were recorded with a wireless surface EMG system (Delsys Trigno, Boston, USA). The muscles chosen are commonly assessed in gait analysis studies with and without FOs (Murley et al., 2009) and represent muscle groups that are greatly solicited during walking. Skin impedance was reduced by shaving, abrading with fine-grade sandpaper and wiping with alcohol swabs. The EMG electrodes positioning was carried out according to the SENIAM recommendations (Hermens et al., 2000). The electrodes (27 mm × 37 mm × 15 mm) were 99% silver contact material with a four-bar formation. The distance between the electrodes was 10 mm. Data were sampled at 1.93 kHz. The gain was 1000; the maximum intraelectrode impedance was 6 kOhm; common noise removal ratio (CNRR) of the EMG amplifier was > 80 dB and a 16 bits A/D
2.2. Foot orthoses The FOs used in this study were fabricated by a certified orthotist technician and were made of a 3.2 mm thick polypropylene shell. These ¾ length FOs had an EVA straight extrinsic rearfoot post, cut at 75% of the length of the heel cup. All FOs had an EVA lateral bar that could easily be removed with a heat gun when needed. FOs were made from plaster casts taken with the subtalar joint held in neutral position, as 9
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Fig. 2. Muscle activity with shoes and FOs with a lateral bar.
lateral bar) one hour the first day, and one hour more each following days until the participant could wear them all day. This protocol is commonly used in clinical practice to reduce pain and discomfort experienced by patients during the first days of wearing orthoses. Then, participants had to wear the assigned orthoses in their everyday activities for one month. Everyday, participants completed a logbook in which they had to quantify the level of pain felt when wearing the orthoses on a visual analog scale ranging from 0 to 10 and to report the number of hours they were worn. After the adaptation period, participants attended their first experimental session at UQTR’s gait analysis laboratory. The experimental protocol consisted of walking on a 10 m walkway with and without the assigned orthoses as fast as they could, without running. Participants were first asked to perform five familiarization trials. During these trials, walking speed was recorded with photocells timing gates positioned at 2.5 and 7.5 m on the walkway and was averaged for each participant. Then, five trials were completed in the assigned orthoses and finally five trials in the control condition (shoes only). All trials with walking speed varying from ± 5% of the mean speed established during the familiarization trials were rejected and immediately repeated. A 5-min break was given to the participants between the FOs’ and the control trials. After the first testing session, the experimental conditions were interchanged for all participants: a lateral bar was added to the FOs and was removed from the FOs with a lateral bar. All participants had to wear the new orthoses in their everyday activities for the next month and subsequently completed the second testing
converter was used. The EMG data were filtered with a zero phase lag, bi-directional, 20–450 Hz bandpass fourth-order Butterworth filter and full-wave rectified. Analyses were performed on the EMG data root mean square (RMS), calculated with a moving window of 50 ms width with an overlap of 25 ms and were visually inspected for movement artifact or crosstalk. RMS data were normalized with the mean peak RMS of all trials of the control condition for each testing session. To determine the initial contact of the foot, an accelerometer (Delsys Trigno, Boston, USA) was positioned on the tibial tuberosity of the participant’s tested leg. The initial contact was defined as the peak amplitude of the accelerometer curve as described by Mizrahi et al. (2000). The accelerometer’s sampling rate was 148.15 Hz. All measurements were recorded on the leg of the participant that presented the lowest FPI score. If no differences were observed between both feet, the dominant leg (Moisan and Cantin, 2016) was chosen. Three strides by trial were used for the analyses, for a total of 15 strides evaluated for each condition for each speed. 2.4. Protocol Approximately two weeks after the plaster casts were made, the experimental conditions were dispensed to the participants. Seven participants were randomly asked to wear FOs and eight participants were asked to wear FOs with a lateral bar. One of the researchers (GM) confirmed the FOs’ conformity and explained the progressive adaptation protocol consisting of wearing the assigned FOs (with or without a 10
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Fig. 2. (continued)
session during which the same protocol was performed. They had to fill the same logbook to quantify the pain felt when wearing the orthoses and the number of hours they were worn.
No comparison between FOs and FOs with a lateral bar was performed as it has been shown that between-session absolute reliability of EMG data was poor (Moisan and Cantin, 2016, Murley et al., 2010b).
2.5. Analysis
3. Results
The Shapiro-Wilk test value was used to assess normality of descriptive data. As they were not normally distributed, Wilcoxon tests were performed with a level of statistical significance set at p ≤ 0.05 to compare the descriptive data between groups. The D’Agostino-Pearson test was used to evaluate the distribution of EMG data. To compare the effects of experimental conditions on muscle activity between the two conditions, a curve analysis was performed using SPM (Friston, 2007, Pataky, 2012). Each individual stride was normalized to 100% according to its duration. To compare the differences between each normalized point of the curves, the non-parametric permutation method test (SnPM) (Nichols and Holmes, 2002, Pataky et al., 2015) was used. The SnPM threshold above which only α = 5% of the data would be expected, had the test statistic trajectory resulted from an equivalently smooth random process, was calculated. The individual probability that each supra-threshold cluster could have resulted from an equivalently smooth random process was determined. Cohen’s d effect sizes and maximum mean differences (MD) were calculated when statistically significant differences were observed. All EMG analyses (D’AgostinoPearson and permutation tests) were implemented using the open access SPM1D code (www.spm1d.org) in Python software (Version 2.7).
No difference was found in the average time the experimental conditions were worn per day during the one-month adaptation periods between testing sessions (FOs: 6.54 ± 1.78 h, FOs with a lateral bar: 5.94 ± 1.85 h, p = 0.14) and in level of pain felt on a 0 to 10 scale when wearing the experimental conditions (FOs: 0.79 ± 1.24, FOs with a lateral bar: 0.93 ± 1.25, p = 0.92). No difference in walking speed was found for FOs (FOs: 2.55 ± 0.56 vs control 2.53 ± 0.54 m/ s, p = 0.39) and FOs with a lateral bar (FOs with a lateral bar: 2.52 ± 0.51 vs control: 2.52 ± 0.48 m/s, p = 0.43) compared to the control condition. For the tibialis anterior muscle, results for the FOs with a lateral bar of one participant had to be excluded from the analyses due to high levels of artifact caused by excessive perspiration. For both experimental conditions, the activity of all muscles was similar compared to the control condition (see Figs. 1 and 2). However, one supra-threshold cluster (44–46%) exceeded the critical threshold of 15.29 as the activity of the gastrocnemius lateralis muscle was significantly increased with FOs (Fig. 1e). The precise probability that a supra-threshold cluster of this size would be observed in repeated random samplings was p < 0.01, the Cohen’s d effect size was 0.32 and MD was + 28% (at 45% of the gait cycle). One supra-threshold cluster 11
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the SALRE theory (Kirby, 2001). Participants with cavus feet present less peak ankle eversion (Powell et al., 2011) and more lateral ground reaction forces (Hillstrom et al., 2013) compared to population with flatter feet during walking. It can be hypothesized that the medial longitudinal arch of the 3.2 mm polypropylene FOs’ shell could counterbalance the effects of the lateral bar for this population that already has a more inverted gait pattern. Future studies should consider using a thinner and more flexible FOs’ shell or add a valgus wedge as it has been shown that it increases external ankle eversion moment (Telfer et al., 2013b). Researchers should also consider assessing other biomechanical parameters such as kinematics and kinetics to better interpret the EMG differences and better understand the underlying FOs mechanism of action. Also, the absence of results for muscles such as fibularis longus, tibialis anterior and gastrocnemius medialis compared to previous studies that found significant differences when wearing FOs (Dedieu et al., 2013, Moisan and Cantin, 2016, Murley and Bird, 2006, Murley et al., 2010a) could perhaps be explained by the analyses performed. As mentioned previously, most studies that assessed the effects of FOs on muscle activity used a traditional zero-dimensional approach to analyze one-dimensional datasets. This implies that the results have a high risk of having yielded statistical significance when, in fact, they were only false positive results. The results of previous studies are not entirely invalidated because large effects, when present, can generally be observed irrespective of the analysis procedure (Pataky et al., 2016). However, smaller effects should be interpreted with caution. Further studies using a unidimensional approaches are needed to confirm or infirm the results of the previous studies. The difference between studies could also be explained by the heterogeneity between the recruited participants. A number of limitations should be taken into account. First, only asymptomatic participants were recruited for this study whereas FOs are mainly prescribed for patients with musculoskeletal pathologies. These results should be extrapolated with caution to a symptomatic population. Second, during the one-month period of wear before each testing session, the participants wore the experimental conditions in their own shoes. By using standardized shoes during the experimental protocol, it was possible to control confounding variables. However, it may not have been representative of their everyday shoes. Third, the fast walking speed chosen in this study limits the external validity of the results. The mean walking speed of the participants of this study may not be reachable for males over 50 years old and females over 40 years old (Bohannon, 1997) or for symptomatic individuals.
(77–78%) also exceeded the critical threshold of 15.62 as the activity of the tibialis anterior muscle was significantly decreased with FOs with a lateral bar with p = 0.01, d = 0.27 and MD was −15% (at 78% of the gait cycle) (see Fig. 2h). 4. Discussion The main objective of this study was to quantify the effects of FOs with and without a lateral bar on muscle activity of participants with cavus feet. When assessing the effects of FOs on muscle activity compared to a control condition, an increased gastrocnemius lateralis activity from 44 to 46% of the walking cycle with a MD of +28% was observed. This significant difference occurred in the peak amplitude region during the beginning of the propulsion phase of walking. It has been shown that peak gastrocnemius lateralis muscle activity occurs around 40 to 45% of the walking cycle, which corresponds to the time the heel lifts from the ground (Clancy et al., 2004). When visually comparing the curves with and without FOs for this muscle (see Fig. 1), one can note that they separate from each other through a significant portion (37–51%) of the gait cycle. Even if the differences are not statistically significant throughout this period, such differences could be of clinical significance. However, it is still unknown how much changes (increase or decrease) in muscle activity is needed to produce a clinical impact. Future studies should include EMG assessments and pain evaluation with a longitudinal experimental protocol to try to determine the minimal clinically significant EMG differences for symptomatic individuals. As mentioned earlier, participants with cavus feet have less peak ankle eversion (Powell et al., 2011) and more lateral ground reaction forces (Hillstrom et al., 2013). According to the SALRE theory (Kirby, 2001), it can be hypothesized that the medial longitudinal arch of the FOs creates an inversion moment around the subtalar and ankle joints axes during the end of the midstance and the beginning of the propulsive phases of gait. For these individuals that already have a more inverted gait pattern, the gastrocnemius lateralis muscle might compensate this increased load by increasing its activity. One can hypothesize that adding a lateral bar to the FOs creates a pronatory moment around these joints and therefore cancelling the effects of the medial longitudinal arch, explaining the absence of EMG differences when comparing FOs with a lateral bar to the shod condition. This result is not consistent with previous studies that quantified the effects of FOs on peak gastrocnemius lateralis muscle activity, in which no difference (Telfer et al., 2013a) and a decreased activity (Moisan and Cantin, 2016) was observed. The heterogeneity of participants’ foot type, walking speed and FOs used could perhaps explain the variability of results across studies. However, the results of this study are novative as the effects of FOs on muscle activity of participants with cavus feet during fast walking have never been previously studied. When comparing FOs with a lateral bar and the control condition effects on muscle activity, a decreased tibialis anterior activity from 77 to 78% of the walking cycle was observed. The effects of different types of FOs on the activity of the tibialis anterior muscle are inconsistent in previous studies. Indeed, no difference (Murley et al., 2010a, Telfer et al., 2013a), a decreased activity (Dedieu et al., 2013, Moisan and Cantin, 2016) and an increased activity (Tomaro and Burdett, 1993) were previously observed. However, only one study assessed FOs with a lateral bar and found no difference during the stance phase of walking (Moisan and Cantin, 2016). Considering the very short period of time the supra-threshold cluster exceeded the critical threshold and the small Cohen’s d effect size, this result should be interpreted with caution. Based on earlier published data, we hypothesized that the activity of the fibularis longus muscle would be decreased with FOs with a lateral bar (Moisan and Cantin, 2016). The lack of significant differences could perhaps be explained by the type of FOs used. As previously mentioned, the clinical goal of adding the lateral bar to the FOs is to increase the pronatory moments across the ankle and subtalar joints according to
5. Conclusion This study suggests that FOs with a lateral bar have very limited effects on lower limb muscle activity of participants with cavus feet during fast walking. The study also suggests that the gastrocnemius lateralis muscle activity is increased with FOs in the early stages of the propulsion phase during fast walking. This result will help researchers and clinicians better understand the effects of different FO types on muscle activity of individuals with cavus feet.
Conflict of interest The authors declare that they have no conflict of interest relating to the material presented in this article.
Acknowledgements This study was funded by the Canadian Institutes of Health Research (CIHR) and the Fonds de Recherche du Québec-Santé (FRQS) through scholarships received by the first author. 12
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Appendix A. Supplementary matreial
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Gabriel Moisan received his M.Sc. in kinesiology at ‘‘Université du Québec à Trois-Rivières ” (UQTR), Canada, in 2015, where he is currently pursuing a doctoral degree in biomedical sciences. He is also involved in research conducted by the ‘‘Groupe de Recherche surles Affections Neuro-musculo-squelettiques’’ (GRAN). His primary research interests are locomotion, foot and ankle biomechanics and foot orthoses.
Martin Descarreaux received his Ph.D. from ‘‘Université Laval’’, Canada, in 2004. He is a Full Professor at ‘‘Université du Québec à Trois-Rivières’’ (UQTR)’’, Canada, in the department of Human Kinetics. He is the director of the ‘‘Groupe de Recherche sur les Affections Neuro-musculo-squelettiques’’ (GRAN). His main research interests are motor control and proprioceptive deficits associated with chronic and recurrent low back pain.
Vincent Cantin received his Ph.D. from ‘‘Université Laval’’, Canada, in 2009. He is a Full Professor at ‘‘Université du Québec à Trois-Rivières’’ (UQTR), Canada, in the department of Human Kinetics and an active member of the ‘‘Groupe de Recherche sur les Affections Neuromusculosquelettiques’’ (GRAN). His primary research interests are locomotion and foot biomechanics.
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