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Postural adjustment and muscle activity during each phase of gait initiation in chronic ankle instability: an observational study

BMC Sports Science, Medicine and Rehabilitation volume 16, Article number: 248 (2024) Cite this article

Abstract

Background

Gait initiation (GI) can be divided into three sections according to the center of pressure (COP) trace (S1, S2, and S3). Almost all studies do not separate each phase of the GI profile in postural control assessment and muscular investigation, whereas differences in the COP and muscles are found in each phase of the GI profile in people with gait problems.

Methods

Twenty individuals with CAI and twenty healthy controls were included in the present study. A force plate synchronized with Qualisys motion analysis, MEGAWIN electromyography, and a pair of auditory cues were used for data capture. The participants carried out five trials of GI with the affected leg (dominant leg). The peak and mean COP excursions; the mean and maximum velocities of COP excursion during S1, S2,, S3, and the total phases in the mediolateral (ML) and anterior‒posterior (AP) directions; the root mean square (RMS); and the onset activity of the Tibialis Anterior (TA) and Soleus (SOL) muscles for both legs were used for statistical analysis. Independent t tests and Mann‒Whitney U tests were used for statistical analysis on the basis of a significance level of ≤ 0.05.

Results

Compared with those of healthy controls, independent t tests revealed a significant decrease in the peak COP excursion in the AP direction during S2 (P = 0.021) and in the mean velocity of COP excursion in the AP direction during S1 (P = 0.044) in the CAI group. Additionally, there was a significant increase in the duration of S1 in the GI profile (P = 0.045) in the CAI group compared with the healthy control group. There was no significant difference in the other COP variables, TA or SOL RMS or onset activity for either leg during S1, S2, or S3 between the two groups (P > 0.065).

Conclusion

Individuals with CAI exhibit increased stiffness in the AP direction in the injured ankle. This leads to a reduction in the velocity and peak of COP excursion, as well as an increase in the time required for postural control adjustment. These findings highlight the challenges individuals with CAI may face in meeting postural demands when trying to unload the affected foot.

Ethical code

IR.SBMU.RETECH.REC.1402.095, 2023–5-28.

Peer Review reports

Introduction

Chronic ankle instability (CAI) is a common and debilitating complication of a primary ankle sprain [1]. CAI is characterized by a patient who is more than 12 months removed from the initial ankle sprain; has a propensity for recurrent ankle sprains; and experiences frequent episodes or perceptions of the ankle giving way, as well as persistent symptoms such as pain, swelling, diminished range of motion, weakness, and reduced self-reported function [2]. Changes in sensorimotor function have been identified as one of several functional and mechanical contributions to CAI [3, 4]. Sensorimotor modifications are associated with deficits in postural control and deviation in gait [5]. Changes in single-limb postural control have been observed in individuals with unilateral CAI, suggesting that there may be changes in feed-forward mechanisms [6].

Gait initiation (GI) is defined as the temporary shift from quiet standing to a single-leg position [7]. The GI tract is a functional task that can be assessed through feed-forward and feedback neuromuscular motor control [6, 8]. The GI profile is divided into three sections. Briefly, the first section (S1) begins at t0 and is the time when the center of pressure (COP) trace deviates posteriorly from the initial swing limb [9, 10]. S1 ends with the COP located in its most posterior-lateral position toward the initial stepping foot [11]. This posterior–lateral shift requires bilateral inhibition of the soleus (SOL), followed closely by bilateral activation of the tibialis anterior (TA) [12, 13]. The second section (S2) represents the movement of the COP medially toward the initial stance foot and ends under the initial stance foot on which the COP begins to move forward [11]. The swing foot is responsible for postural alterations during S1 and S2 [7]. The third section (S3) extends from the end of S2 until the toe-off in the initial stance foot as the COP translates forward [11]. During S3, the ipsilateral TA and SOL must be activated to pull the center of mass (COM) forward while also controlling forward motion [7, 14]. Studies have reported the anticipatory postural adjustment (APA) phase as the initiation command until the end of S1 [15,16,17]. In line with this definition, S2 plus S3 defines the execution phase [18].

Studies that have investigated the GI profile in individuals with CAI have shown that these individuals modulate the S1 plus S2 phases of the GI profile more than healthy controls and spend less time in these phases [19]. However, two studies by Ebrahimabadi et al. reported that the peak of medial‒lateral (ML) excursion of the COP from the auditory cue until S1 is shorter in individuals with CAI than in healthy controls [20, 21]. Hass et al., who evaluated each phase of the GI profile separately, reported that individuals with CAI did not show any difference in peak COP excursion during each phase of the GI profile compared with healthy controls when the GI was with the affected leg [11]. On the other hand, one study reported a similar velocity of COP excursion during S2 plus S3 in the ML direction compared with healthy controls [20]. Another study has shown that the velocity of COP displacement in the ML direction during S3 is greater in individuals with CAI than in healthy controls [11]. The conflicting results concerning the alteration of the COP during GI originated from the analysis of the COP during GI as a combined phase, not in the separation of each phase. Therefore, the exact separation of GI phases is fundamental for understanding the exact differences in the GI profile between individuals with CAI and healthy controls.

In healthy young adults, the predominant pattern of muscle activity that results in posterior displacement of the COP during the GI is bilateral inhibition of soleus activity, closely followed by bilateral activation of both legs’ tibialis anterior [12, 13]. Mickelborough et al. reported the tendency for muscle activity to be more variable in the different phases of GI. They suggested that the preparatory phase may be a particular source of difficulty in patients with high-level gait disorders [14]. Khanmohammadi et al. reported that the activity of the TA and SOL muscles during S2 plus S3 of the GI profile is greater in older subjects than in younger subjects [22], which suggested that muscle behaviors change at different phases of the GI profile [22]. Research on the muscle activity during GI in individuals with CAI has limited to the only one study [19]. The results of this study revealed delayed inhibition in the SOL muscle of the affected leg during the preparatory phase of the GI in individuals with CAI, whereas the onset activity of the TA muscle did not differ between individuals with CAI and healthy controls. This study did not find any significant difference between the two groups in terms of the amount of muscle activity during the S1 plus S2 of the GI [19]. On the basis of previous reports, the muscle activity in each phase of the GI could differ [14]. Therefore, investigating COP excursion during the GI phase simultaneously with muscle activity could be important for better understanding muscle activation during the GI phases in individuals with CAI.

Therefore, since past studies in the GI profile have not investigated the displacement of the COP synchronized with muscle activity separately by phase between individuals with CAI and healthy controls [11, 19,20,21, 23], we decided to study the COP parameters and muscle activity in each phase of the GI profile (S1, S2, and S3) according to the definitions of Hass et al. [11]. This study aimed to investigated the COP parameters and muscle activity during S1,S2,S3, and total phases of GI in individuals with CAI and healthy controls. The first hypothesis of this study was that, compared with healthy controls, individuals with CAI would show an altered peak of COP excursion in the AP and ML directions during S1 and S2 but not in S3. The second hypothesis was that the velocity of COP excursion during S1, S2, and S3 would be similar between individuals with CAI and healthy controls. The third hypothesis was that the onset activity of the SOL muscle of the affected leg in individuals with CAI would be earlier than that in healthy controls and that the mean SOL and TA muscle activity during S1, S2 and S3 would not differ between individuals with CAI and healthy controls.

Methods

Sample size

With G-power 3.1.9.2 software and information from 10 samples in each group as a pilot study, the variable of peak COP displacement in the AP direction was analyzed. The mean ± standard deviation for the CAI group was (0.143 ± 0.050), that for the control group was (0.201 ± 0.064), and the Hedges correction effect size was 0.963. A total of 18 samples in each group were analyzed on the basis of these data. By 10% probability drop, a final sample size of 20 samples was calculated for each group.

Participants

A total of 40 subjects, 20 individuals with CAI and 20 healthy controls, participated in the present study (Fig. 1) (Table 1). The available nonrandom sampling method was used to select the participants. Patients with unilateral ankle sprain who had visited the orthopedic office for at least 12 months (12–36 months) prior to the test were included in the present study. Individuals with CAI of the right (dominant) injured limb, aged 18–40 years, were included in the study if they met the following specific criteria: at least one episode of recurrent ankle sprain between 3 and 6 months before participation in the study, at least one episode of giving way within the year [24], a score ≤ 24 on the CAIT (Cumberland Ankle Instability Tools) questionnaire [25, 26], a score of < 90% in daily living activities and < 80% in sport activities, based on the Iranian Foot and Ankle Ability Measure questionnaire (FAAM) [25, 27], reported pain, instability, and/or weakness in the involved ankle, attributed these signs to their initial ankle injury, and failed to resume all pre-injury activities [24]. No clinical test was used to select participants, as CAI is described as repeated ankle sprains and/or episodes of 'giving way' with or without ligament laxity [28]. The exclusion criteria included neurological disorders, chronic lower extremity disorders, acute head injury, lower extremity injuries within three months prior to the test, and bilateral ankle sprain [24]. The control group had no history of ankle sprain or giving way [29]. Limb dominance was determined by asking participants which limb they would use to kick a ball [30]. All the participants signed the consent form provided by the Ethical Committee of Shahid Beheshti University of Medical Sciences with the number “IR.SBMU.RETECH.REC.1402.095” and approval date of “2023-05-28”.

Fig. 1
figure 1

Flowchart of participant selection

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Table 1 The frequency distributions of sex and the means and standard deviations of the background variables in each group
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Procedures

First, the participants ran for 15 min around the laboratory to warm. They then completed the CAIT and FAAM. The location of the electromyography (EMG) electrodes on both legs was shaved, and were cleaned with alcohol. Two AG/AGCL electrodes were attached to the identified location on both legs via the SENIAM [31]. The EMG (ME6000-T8) was synchronized with the force plate and Qualisys motion system to capture the data. The participants stood barefoot on the faceplate and adopted a self-selected stance. Four reflective markers adhered to the heels and big toes of the participants to detect stance width and foot length. Stance width and foot length were used for normalization of the COP data in the ML and AP directions, respectively. Two auditory cues with 2-s intervals were presented before the GI. All systems were synchronized in time. The first audible signal was applied at 5.4th seconds, and the second was applied at 7.4th seconds. The times that the two auditory cues ran was consistent across all the subjects and all the trials. The intensity, duration and frequency of both auditory stimuli are 60 dB, 100 ms and 2 kHz, respectively [32]. The participants were instructed to initiate the gait after the second cue at their self-selected speed until they had completed at least two strides. The subjects did not receive any specific instructions on speed or stance width to allow for natural behavior [33]. The data were checked after each trial to ensure that the subjects did not step after the presentation of the first cue or with the unaffected leg. The subjects were familiarized with the test by conducting two or three experimental trials before the main trial. All the participants initiated gait 5 times via the right limb. All participants had limb injuries on their dominant side (right side); therefore, the dominant limb of the control group was used for analysis.

COP measures

A synchronous motion analysis system with a force plate (40* 60 cm) (Kistler Instrument Corp, Switzerland's model 9287BA) with a sampling frequency of 1000 Hz was used to collect the data. The participants stood barefoot on the force plate, received a pair of auditory stimuli through the sound system of a computer located one and a half meters away, and carried out five trials of GI until two stride with the right leg after the second cue. The Qualisys Track Manager (QTM) software was used to capture the force data, which were subsequently exported to tab separated values (TSVs). The ground reaction force (GRF), moment and COP in three directions (ML, AP, and vertical) were calculated directly via the QTM software. The average of each dependent variable in three trials was used as the data for analysis.

Electromyography measurements

The SOL and TA muscles of both limbs were examined via EMG. The EMG test was carried out via a MUSCLE TESTER (MEGAWIN device manufactured in Finland, model ME6000-T8, with a sampling frequency of 1000 Hz). AG/AGCL surface electrodes with a 20 mm interelectrode distance integrated with a differential preamplifier were placed on the skin on the SOL and TA muscles of both legs according to the SENIAM protocol [34]. The EMG data were filtered (using a Butterworth filter with second-order zero delay and cutoff frequencies of 20 Hz and 450 Hz). The response times of the TA and SOL muscles related to COP onset (t0) were calculated [35]. The average root mean square (RMS) activity of these muscles was calculated during each phase of the GI profile. It was necessary to measure the maximum voluntary isometric contraction (MVIC) of the TA and SOL muscles to normalize their activity. The normalized activity of the TA and SOL was calculated via the equation "(mean RMS in each phase of the GI/maximum RMS in MVIC)*100". The MVIC test of these muscles was performed three times, with a 5 s duration and a 5 s rest interval. The soleus MVIC was tested while the subject was seated in a chair with 90–90 degrees of flexion of the hip and knee. A stiff box was placed under the subject's midfoot, while a stiff strap was drawn from beneath the stiff box, up the thigh to prevent further hip flexion. The therapist's hand was placed over the knee and secured to the floor, providing resistance for the maximal test. The subjects were asked to perform plantar flexion against the floor [36]. The TA MVIC was tested in a seated position with the knee flexed to 90 degrees. The subjects carried out dorsiflexion and inversion against a fixed plate above the foot (Fig. 2) [37].

Fig. 2
figure 2

MVIC in the soleus and tibialis anterior muscles

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Data processing

A customized program (Math Works Inc., R2021a) was utilized for data processing in MATLAB. The GRF was collected with a sampling frequency of 1000 Hz. The program calculates the AP and ML COP force plate data and presents it with TSV output [19]. The COP trace of GI was divided into three phases: S1 starts at t0 and is the time when the COP trace deviates posterior-laterally from the initial swing limb [9, 10]. The initiation of deviation is the point where the COP excursion in the ML direction exceeds 3 standard deviations of the COP excursion during the 200 ms prior to the onset of the auditory cue [38]. End of S1 is the time, when COP is located in the most lateral position to the swing foot[11, 39]. S2 starts at the end of S1 and continues until the COP trace moves medially to the stance foot. S3 starts from the end of S2 and represents the COP trace moving anteriorly to the stance foot to generate forward body movement (Fig. 3) [11]. A cutoff threshold of 5 newtons (N) in the vertical GRF (Fz) was used to determine when the stance foot left the force plate, indicating the completion of the GI profile. COP data were filtered (using a Butterworth second-order zero delay low-pass filter at 10 Hz). The start of the GI (t0), end of S1, end of S2, and end of S3 and their related frames are obtained from the force-plate signal. According to the updated frame, the average RMS of the corrected EMG signal is obtained to represent muscle activity. Muscle response time occurs when the EMG activity exceeds 3 standard deviations during quiet standing [40]. The onset time of these muscles is calculated relative to t0 [35].

Fig. 3
figure 3

COP trace during GI. COP: cemter of pressure. GI: gait initiation. ML: (medial–lateral), AP (anterior–posterior). S1: phase 1 of GI, S2: phase 2 of GI, S3: phase 3 of GI, Cue: auditory stimulus

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The postural control outcome measures included the mean and peak COP excursion, and the mean and maximum velocities of COP excursion during each phase and the total phases of the GI in the ML and AP directions. The duration of each phase was calculated on the basis of the percentage of time in each phase. COP excursions and velocities were normalized to the stance width and foot length of the corresponding trial for each participant [11]. Muscle outcome measures included the SOL and TA onset activity related to t0 and (%MVIC) activity of these muscles during each phase of the GI profile bilaterally. The weight distribution during quiet standing on both legs was analyzed by measuring the deviation of the COP in the ML and AP directions as the mean ± 3 standard deviations from baseline [41]. The velocity of gait initiation was determined by calculating the average initial step velocity from heel off to heel strike of the first stepping foot [42, 43]. It was necessary to check the weight distribution and movement velocity to ensure that the groups had comparable standing and temporal-spatial gait characteristics.

Statistical analysis

SPSS version 27 was used for statistical data analysis. The normality of the distribution of the data was checked via the Kolmogorov‒Smirnov test. Independent Student’s t tests were used to analyze all normally distributed variables in each phase. The Mann‒Whitney U test was used to analyze all abnormal variables. The chi-square test was used to assess the distribution of sex in both groups. The means and standard deviations of the dependent variables were calculated for each individual. Hedges’ correction effect size was used for point estimation of each variable. Hedges’ g = 0.16, 0.38, and 0.76 for group difference research were interpreted as small, medium, and large effects, respectively [44].

Results

The Kolmogorov‒Smirnov test revealed that some variables had a normal distribution, whereas others had an abnormal distribution. The chi-square test and Mann‒Whitney U test revealed that there was no significant difference in the demographic data between the two groups (P > 0.197) (Table 1). The demographic data of the CAI group were [aged 27.20 ± 9.13 years, height 170.10 ± 6.88 cm, and weight 68.44 ± 10.86 kg], and those of the healthy control group were [aged 26.75 ± 6.38 years, height 170.55 ± 11.18 cm, and weight 70.60 ± 11.66 kg]. Student’s t test revealed that the movement velocity did not differ between the two groups (P > 0.113) (Table 1).

COP results

Independent t tests revealed a significant decrease in the peak COP excursion in the AP direction during S2 (P = 0.021) and in the mean velocity of COP excursion in the AP direction during S1 (P = 0.044) in the CAI group compared with the healthy control group. Additionally, there was a significant increase in the duration of S1 in the GI profile (P = 0.045) in the CAI group compared with the healthy control group (Table 2). There was no significant difference between the two groups in terms of the other variables (P > 0.065).

Table 2 The means and standard deviations of the COP measurements for each group
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EMG results

There was no significant difference between the groups in the onset activity of both the SOL and TA muscles relative to that at t0 (P > 0.293). TA and SOL muscle activity in each phase did not significantly differ between the two groups (P > 0.372) (Table 3) (Figs. 4 and 5).

Table 3 The means and standard deviations of the EMG measurements for each group
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Fig. 4
figure 4

Electromyography onset and activity of the SOL and TA muscles of both legs during GI. Arrow head: inhibition of the right soleus. Arrow: activation of the right soleus. GI: Gait Initiation. S1: Phase 1 of GI, S2, Phase 2 of GI, S3: Phase 3 of GI, Cue: Auditory stimulus. TA: tibialis anterior, SOL: soleus

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Fig. 5
figure 5

The raw electromyography onset and activity of the SOL and TA muscles in both legs during GI. Arrow: Activation of the right soleus. GI: Gait Initiation. S1: Phase 1 of GI, S2, Phase 2 of GI, S3: Phase 3 of GI, Cue: Auditory stimulus. TA: tibialis anterior, SOL: soleus

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Discussion

The purpose of the present study was to evaluate the COP parameters and muscle activity in each phase of the GI profile separately (S1, S2, and S3) and total phases. The first hypothesis was that, compared with healthy controls, individuals with CAI have an altered peak of COP excursion in the AP and ML directions during S1 and S2 but not in S3. The findings partially supported the first hypothesis and showed that individuals with CAI had a decreased peak in COP excursion in the AP direction during S2, whereas there was no difference between the two groups in terms of COP excursion in the ML direction during S1, S2, or S3.

The present study examined S1, S2, and S3 separately and revealed that, compared with healthy controls, individuals with CAI had a reduced peak of COP excursion in the AP direction during S2. The findings did not reveal any difference in the peak COP excursion in the ML direction during each GI phase. Some studies disagree with the present findings [20, 21]. Previous studies have shown that the non-normalized peak of COP excursion (relative to stance width and foot length) in the ML direction during S1 was shorter than that in healthy controls [20, 21]. However, these studies revealed that there was no difference in the non-normalized peak of COP excursion in the AP direction during S1 between the two groups, regardless of whether the GI was with the affected leg or with the non-affected leg [20, 21]. The lack of normalization of the COP data in the studies by Ebrahimabadi et al. may explain this discrepancy [45]. In addition, Yousefi et al. reported that, compared with healthy controls, individuals with CAI did not show any difference in terms of the normalized peak of COP excursion in the AP and ML directions during S1 plus S2 [19]. This finding contradicts the present findings. Owing to differences in COP data processing methods, Yousefi et al. considered S1 plus S2 as the preparatory phase [10, 25,26,27,28] and evaluated these phases together, which affected the final results. Hass et al. did not find a significant difference in the normalized peak of COP excursion during each phase of the GI in the ML and AP direction tract between individuals with CAI and healthy controls when the GI was with the affected leg [11]. Hass et al. used two force plates for COP data capture, resulting in a wider stance width for the participants. Notably, a wider stance width prior to GI could impact COP excursion [46].

During quiet stance, the COM is coupled with the COP in the transverse plane to establish postural control [47]. As movement is initiated, with the heel rising at the end of S1 [12], the COM and COP must uncouple and move in opposite directions to create the forward momentum required for locomotion [47]. This COP-COM separation serves as an indicator of disability during the GI [47]. The raising of the leg results in COP‒COM separation, which evokes the sensation of falling [48,49,50]. Individuals with balance or proprioceptive deficiencies shorten this distance to maintain or enhance their balance control [47]. Individuals with CAI have an increased risk of falling at least once a year [2, 4]. Owing to their fear of falling again and the need to maintain postural stability, they tend to reduce the peak of COP excursion in the AP direction when the leg is raised (S2) to maintain their posture within the limits of their base of support.

The second hypothesis was that the velocity of COP excursion during S1, S2 and S3 would be similar between individuals with CAI and healthy controls. The results of the present study partially rejected the second hypothesis that individuals with CAI had a reduced mean velocity of COP excursion in the AP direction during S1 compared with healthy controls, whereas the rate of COP excursion did not differ between the two groups in the other phases and direction. Additionally, individuals with CAI require more time to complete S1. These findings are consistent with each other. A decrease in speed in one phase logically results in an increase in the duration of that phase. At the GI, the swing leg is responsible for the displacement of the COP during S1 and S2 [7] to generate a propulsive force toward the stance leg medially [48]. Individuals with CAI appear to require more time to adjust their postural requirements for posterior displacement in the sagittal plane, which aligns with the initial ankle sprain [51]. These individuals exhibit greater stiffness in the AP direction in the injured ankle [52], which reduces the velocity of COP excursion to control posture. In contrast to the findings of the present study, previous studies have suggested that individuals with CAI spend less time in S1 plus S2 [19, 23]. The reason for this discrepancy was the method of COP trace processing and the number of auditory cues used in the present study. The method of signal processing in the present study was based on the first deviation of the COP and the separation of phases (such as Haas et al.[11], which consider t0 the start of S1 until the most posterior-lateral shift of the COP, whereas other studies considered signal processing from the auditory cue to the end of S2 [19, 23]. In the present study, there were two auditory cues with a 2-s interval, whereas other studies used only one auditory cue [19, 23]. The participants in the present study were required to pay attention to the second cue to initiate gait. It has been reported that attentional resources during step preparation influence the release of APAs over a longer period of time [53].

The third hypothesis was that the onset activity of the SOL muscle in the affected leg of individuals with CAI would be earlier than that in healthy controls and that the mean activity of the SOL and TA muscles during S1, S2 and S3 would not differ between individuals with CAI and healthy controls. The results of this study showed that individuals with CAI do not exhibit any difference in the onset activity of the SOL or TA muscles in the affected or unaffected leg compared with healthy controls when the GI is with the affected leg. These results contradict the findings of Yousefi et al. [19], who reported that the SOL muscle of the affected leg in individuals with CAI was inhibited later than that in healthy controls. They also reported that TA onset activity did not differ between individuals with CAI and healthy controls [19]. This discrepancy arises from the terms “inhibition” and “onset activity”. SOL muscle inhibition occurs before t0 [7], but SOL muscle activation occurs between heel off and toe off in individuals with a normal gait [54]. This means that during the GI profile, the heel off corresponds to the end of S1[10], and the toe off corresponds to the end of S2[55]. Therefore, the onset time of the SOL muscle is different from the inhibition of this muscle during quiet standing. On the other hand, SOL inhibition and TA activation patterns are not always observed in young adults; i.e., the SOL is not always inhibited before the TA is activated [48, 56]. Other authors propose that variability is inherent and functional and that variability in movement is necessary for changes in the coordination of movement [57,58,59]. It was reported that during the GI profile, two-thirds of elderly subjects showed the earliest activation of the swing leg medial gastrocnemius after COP onset, whereas one-third of elderly people showed the earliest activation of the swing leg medial gastrocnemius after the releasing phase (S1) [14]. Therefore, variation in the onset activity of the SOL and TA muscles during GI may be present in individuals with CAI, similar to other people with gait problems. In other words, each subject who had CAI could experience a combination of impairments that are patient-specific [2]. The large standard deviation (Table 2) in the onset activity of the SOL and TA muscles indicates variability in the onset activity of these muscles.

The findings revealed that there was no difference in the RMS activity (%MVCI) of the SOL or TA muscles bilaterally during S1, S2, or S3 between individuals with CAI and healthy controls. The results of the present study are in agreement with the findings of Yousefi et al., who reported that the RMS activity of the TA and SOL did not differ between individuals with CAI and healthy controls [19]. The GI is a simple task on the ground with a very small created force [7]. There are no differences in RMS muscle activation during walking on the ground between individuals with CAI and healthy controls [60]. The results of RMS activity of the SOL and TA muscles have shown the great standard deviation (Table 2). This means that variability in the human movement is necessary for changes in the coordination of movement [57,58,59]. Additionally based on the Hertel et al. model, motor output arises from self-organization when taking action. Movement is a natural part of being human, and the body will adapt to overcome limitations in order to complete necessary tasks [2]. Therefore this variability in muscle actions could explain the lack of differences in RMS activity between the two groups.

Like other investigations, this study had several limitations. The present study did not measure SOL inhibition or COP-COM separation, which are key factors in balance control. The inhibition of the SOL muscle related to the cue or COP onset and COP‒COM separation should be measured in future studies. Kinesiophobia, as a significant factor for measuring the risk of re-injury, should be added to the literature concerning the GI. The participants in the present study had experienced at least one lateral ankle sprain at least 12 months prior to the test. The individuals with CAI varied in the time of the first lateral ankle sprain between 12 and 36 months; therefore, it would be better to control the homogeneity of first-time ankle sprain in individuals with CAI.

Conclusion

The findings of the present study show that individuals with CAI reduce the peak of COP excursion in the AP direction because of the separation of the COP-COM to maintain postural stability within the base of support. These individuals exhibit greater stiffness in the AP direction in the injured ankle, which reduces the velocity of COP excursion for postural control. Additionally, individuals with CAI appear to require more time to adjust their postural requirements for posterior displacement in the sagittal plane, which aligns with the initial ankle sprain. As a result of the reduced velocity, they lengthen S1. This study recommends that individuals with CAI, who initially experience an ankle sprain in the ML direction, should focus on postural control exercises in both the AP and ML planes during rehabilitation programs. Additionally, since these individuals exhibit weakness in the feed-forward mechanism of postural control, the study suggests comprehensive rehabilitation that emphasizes postural adjustments following predictable perturbations.

Data availability

The datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request.

Abbreviations

AP:

Anterior-Posterior

APA:

Anticipatory postural adjustment

CAIT:

Cumberland Ankle Instability Tools

COP:

Center of Pressure

COM:

Center of mass

CAI:

Chronic ankle instability

EMG:

Electromyography

FAAM:

Foot and Ankle Ability Measure

GRF:

Ground reaction force

GI:

Gait initiation

MVIC:

Maximum voluntary isometric contraction

ML:

Medial–Lateral

N:

Newton

QTM:

Qualisys Track Manager

RMS:

Root mean square

SD:

Standard Deviation

SOL:

Soleus

S1:

Phase 1 of gait initiation

S2:

Phase 2 of gait initiation

S3:

Phase 3 of gait initiation

TA:

Tibialis Anterior

TSVs:

Tab separated values

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Acknowledgements

We appreciate the Neuromuscular Rehabilitation research center at Semnan University of Medical Science and Health Service. Additionally, we are grateful to all the participants who took part in our study. Special thanks to Dr. Sam Soroush Nia for providing us with information on patients who have experienced lateral ankle sprains, and to Mr. Yaghoub Shavehei for assisting with data capture.

Funding

No funding was received for conducting this study.

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Authors and Affiliations

  1. Physiotherapy Research Center, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran

    Marzieh Mortezanejad, Zahra Ebrahimabadi & Abbas Rahimi

  2. Neuromuscular Rehabilitation Research Center, Semnan University of Medical Sciences, Semnan, Iran

    Marzieh Mortezanejad & Fatemeh Ehsani

  3. Biomedical Engineering Department, Semnan University, Semnan, Iran

    Ali Maleki

  4. Proteomics Research Center, Department of Biostatistics, School of Allied Medical Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran

    Alireza Akbarzadeh Baghban

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  1. Marzieh Mortezanejad
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  2. Zahra Ebrahimabadi
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  3. Abbas Rahimi
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  4. Ali Maleki
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  5. Alireza Akbarzadeh Baghban
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  6. Fatemeh Ehsani
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Contributions

M.M., Z.E, A.R contributed to the study design and conception. M.M. performed the data collection. A.M. developed the MATLAB code. A.A.B, M.M., and Z.E performed the statistical analyses and interpretation of the data. Z.E and M.M. wrote the original draft. F.E. and Z.E. revised the manuscript. All authors reviewed the manuscript for important intellectual content and approved the final version submitted for publication.

Corresponding author

Correspondence to Zahra Ebrahimabadi.

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Ethics approval and consent to participate

Initially, the aim of the study was explained to the participants. They were assured that their information would remain confidential. They were also informed that participation was completely voluntary and that they had the right to withdraw from the study whenever they wished.

Informed consent was obtained from each participant prior to study participation. The study was approved by the Ethics Committee at the Shahid Beheshti University of Medical Sciences (IR.SBMU.REC.1402.095) and was carried out in accordance with the principles of the Declaration of Helsinki.

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The participant gave written informed consent for her/his personal or clinical details along with any identifying images to be published in this study.

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The authors declare no competing interests.

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Mortezanejad, M., Ebrahimabadi, Z., Rahimi, A. et al. Postural adjustment and muscle activity during each phase of gait initiation in chronic ankle instability: an observational study. BMC Sports Sci Med Rehabil 16, 248 (2024). https://doiorg.publicaciones.saludcastillayleon.es/10.1186/s13102-024-01033-x

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Keywords

BMC Sports Science, Medicine and Rehabilitation

ISSN: 2052-1847

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