Balance Training With Stroboscopic Glasses and Neuromechanics in Patients With Chronic Ankle Instability During a Single-Legged Drop Landing
Therapeutic interventions for individuals with chronic ankle instability (CAI) are recommended to improve muscle strength, postural control, and range of motion. However, their effects on neuromechanics during a drop landing remain unclear. In addition, even though therapeutic interventions with stroboscopic glasses appear to effectively improve postural control, how they affect landing neuromechanics remains unclear. To identify the effect of balance training with stroboscopic glasses on neuromechanics during a single-legged drop landing in patients with CAI. Randomized controlled clinical trial. Laboratory. A total of 50 participants with CAI were randomly assigned to 1 of 2 groups: strobe (n = 25; age = 22 ± 3 years, height = 174.7 ± 8.2 cm, mass = 71.8 ± 12.2 kg) or control (n = 25; age = 21 ± 2 years, height = 173.1 ± 8.3 cm, mass = 71.1 ± 13.5 kg). The 4-week rehabilitation (3 sessions per week) included hop-based tasks and single-legged stance. The strobe group wore stroboscopic glasses during the training, whereas the control group did not. Ankle-, knee-, and hip-joint kinematics and 4 lower extremity muscle activations 150 milliseconds before and after initial contact during a single-legged drop landing in the 2 groups. The strobe group showed greater eversion (from 150 milliseconds before to 30 milliseconds after initial contact) and dorsiflexion (from 30 to 96 milliseconds after initial contact) angles and peroneal longus (from 35 milliseconds before to 5 milliseconds after initial contact) and tibialis anterior (from 0 to 120 milliseconds after initial contact) activation in the posttest than the pretest. Patients with CAI who underwent a 4-week rehabilitation with stroboscopic glasses demonstrated changes in neuromechanics, including increased ankle-dorsiflexion and -eversion angles and tibialis anterior and peroneus longus activation, during a single-legged drop landing. This finding suggests that use of stroboscopic glasses during rehabilitation could help patients with CAI develop safe landing mechanics.Context
Objective
Design
Setting
Patients or Other Participants
Intervention(s)
Main Outcome Measure(s)
Results
Conclusions
Chronic ankle instability (CAI) describes a condition characterized by residual symptoms after an ankle sprain that include pain, swelling, loss of function, instability, a feeling of “giving way,” and recurrent lateral ankle sprains (LASs).1 According to a recent theoretical model, patients with CAI have pathomechanical, sensory-perceptual, and motor-behavioral impairments.2 Sensory-perceptual and motor-behavioral impairments are closely related in the population with CAI, but precisely how these impairments are related remains unclear.2 Researchers need to examine how improving sensory-perceptual function through an exercise program can affect motor-behavioral function in patients with CAI.
Lateral ankle sprains occur during functional activities such as running, cutting, jump-landing, and landing-cutting movements.3 Common to these activities is the requirement that the individual stabilize the ankle joint when transitioning from the flight or aerial phase to the initial ground-contact phase.4 To complete this transition without rolling an ankle, individuals should have proper foot and ankle alignment before landing and appropriate muscle activity before and after initial contact to control joint motion during dissipation of the ground reaction forces.5 However, individuals with CAI land in a more plantar-flexed, inverted position and have decreased pre–initial-contact activation of muscles such as the peroneus longus (PL) and the tibialis anterior (TA), which potentially increases the risk for recurrent LASs.6,7 Therefore, therapeutic interventions that can restore appropriate landing neuromechanics should be implemented for patients with CAI to decrease recurrent LASs.
Even though previous therapeutic interventions have been shown to improve postural control, range of motion, and strength in patients with CAI, these physiological variables may not ensure effective or safe movement, or both, during functional movements.8–10 Thus, researchers have investigated landing neuromechanics after therapeutic interventions.4,11,12 According to earlier research, patients with CAI who underwent 6-week hop-stabilization training showed greater dorsiflexion at initial contact and greater TA and PL activation before and after initial contact than patients with CAI who did not receive training.11,12 Based on these studies, therapeutic interventions appear to alter landing biomechanics in a way that could prevent reinjury in individuals with CAI. Adding stroboscopic glasses may improve the effectiveness of these interventions.
Stroboscopic glasses have been used for training in various sports as well as for rehabilitation in patients with CAI.8,13,14 Previous authors reported that patients with CAI who used the glasses showed greater improvements in postural control after rehabilitation compared with patients with CAI who did not use the glasses.8 According to these authors, when proprioceptive exercises are performed with the glasses, the central nervous system adapts by increasing weighting of the remaining proprioceptive inputs. The result may be improved use of somatosensory and vestibular afferent information for managing neuromuscular control.8,15 However, as mentioned, better postural control does not ensure safe landing strategies during physical activities. Furthermore, whether balance training with stroboscopic glasses elicits different landing strategies than those without the glasses is still unknown.
Individuals with CAI have shown proximal adaptations during functional movements such as a single-legged drop landing, landing cutting, and walking.6,16,17 Proximal adaptations such as altered movement strategies, decreased muscle activation, and strength deficits could influence the risk of injury.16 Therefore, an investigation into neuromechanics is needed not only for the ankle joint but also for the knee and hip joints to comprehensively understand movement patterns before and after therapeutic interventions during a single-legged drop landing in individuals with CAI.
The purpose of our study was to conduct a rehabilitation program with stroboscopic glasses to identify the effects on landing neuromechanics in patients with CAI. We hypothesized that a group with stroboscopic glasses would show safer landing strategies, defined by increased dorsiflexion and eversion and greater muscle activation before and after initial contact, during a single-legged drop landing than a group without the glasses. We also hypothesized that a group with stroboscopic glasses would show different proximal neuromechanics compared with a group without the glasses.
METHODS
Participants
Using the guidelines of the International Ankle Consortium, we recruited 50 participants with CAI and randomly assigned them to either the strobe (n = 25) or the control (n = 25) group (Table).18 All participants completed questionnaires associated with the criteria of the International Ankle Consortium. A sample size of 21 participants for each group was determined by a priori power analysis using data from a similar study, with an α level of .05, a β level of .2, and a Cohen d value of 0.8.12 All participants provided written informed consent, and the Institutional Review Board of Brigham Young University approved the study.
Procedures
Our study consisted of a pretest, a posttest, and 12 sessions of the rehabilitation program (Figure 1). On both testing days, participants wore standardized spandex shirts and shorts and athletic shoes. They performed 3 trials of a single-legged drop landing. For these trials, participants were asked to stand on a 30-cm-high box and land on the center of a force plate (model BP600900-2000; AMTI), sampling at 1000 Hz, located 45 cm from the box. They were instructed to step off using the contralateral limb, land on the involved limb with their upper extremities free, and hold the position for 2 seconds. If they could not hold their position for 2 seconds, the trial was counted as a failure and immediately repeated. Participants were given up to 3 practice trials before trials were recorded. For those with bilateral ankle instability, we tested the foot that had the most recent ankle sprain. The stroboscopic glasses were not used for this task.
Citation: Journal of Athletic Training 59, 6; 10.4085/1062-6050-0605.22
For the rehabilitation program, we used a 4-week dynamic balance training program that had been used for patients with CAI in a previous study.9 The training program is specifically focused on hopping and single-legged balance, both of which are thought to be crucial factors to increase the ability to effectively develop spontaneous strategies to execute movement goals and recover single-legged postural control.9 As participants gained proficiency in the program, environmental constraints were added to progressively increase the level of exercises. The strobe group wore stroboscopic glasses during the program, and the degree of opaqueness was increased by adjusting the glasses to higher frequencies as the level of exercises increased. Participants in the strobe group adjusted the strap of the glasses to find their best fit. All participants visited the laboratory to perform the activities 3 times per week for 4 weeks, for a total of 12 sessions; each session lasted 20 minutes. The rehabilitation program was conducted by a certified athletic trainer (H.L. or S.H.). All participants completed the posttest in the same manner as the pretest within a week (4.1 ± 2.5 days).
Analysis of Neuromechanics
During the single-legged drop landing, we collected motion data at 250 Hz using 12 high-speed cameras (Qualisys AB). To track the motion trajectories, we used 44 reflective markers. Twenty-eight reflective markers were placed bilaterally on anatomic landmarks including the anterior- and posterior-superior iliac spines, greater trochanters, medial and lateral femoral condyles, medial and lateral malleoli, posterior heel, dorsal midfoot, medial lateral foot, and between the second and third metatarsals. In addition, rigid clusters of 4 markers were attached bilaterally to the lateral thigh and shank.
Electromyography (EMG) data were collected using 4 wireless surface electrodes (Trigno Wireless Biofeedback System; Delsys) at a sampling rate of 2000 Hz. Rectangular electrodes (27 × 37 × 13 mm) were made of 99% silver contact material with a 4-bar formation. The skin was shaved, scrubbed, and cleansed with 70% isopropyl alcohol to reduce local impedance over the electrode placement. According to the Surface Electromyography for Non-Invasive Assessment of Muscles recommendations, the electrodes were placed on 4 muscles: the TA, PL, gluteus medius (Gmed), and gluteus maximus (Gmax).19 Activation of the Gmed and Gmax was measured because individuals with CAI have shown decreased gluteal muscle activation that could contribute to movement dysfunction.20 The interelectrode spacing was 10 mm. We synchronized the EMG and kinematic data using Visual 3D software (C-Motion).
Data Reduction
All dependent variables were identified during the period from 150 milliseconds before to 150 milliseconds after the initial contact during the task.7 The initial contact was defined as when the vertical ground reaction force exceeded 10 N. Spatial trajectories from the reflective markers were measured using a motion-capture system (Qualisys Track Manager) and imported into Visual 3D software. The trajectories were smoothed using a fourth-order low-pass Butterworth filter with a cutoff of 10 Hz based on a previous similar study.7 A 3-dimensional lower extremity model was created using previously described methods21 to calculate 3-dimensional ankle-, knee-, and hip-joint kinematics: the entire joint-angle curve had 95% CIs. The EMG amplitudes from 3 seconds of a quiet standing position were defined as the reference values for the EMG data.22 Then the EMG amplitudes were zeroed to baseline, rectified, and band-pass filtered from 10 Hz to 500 Hz.23
Statistical Analysis
Functional linear models (P = .05) were used to evaluate differences between 2 times (pretest versus posttest) for ankle-, knee-, and hip-joint kinematics and EMG activation 150 milliseconds before and after initial contact during a single-legged drop landing in the 2 groups (strobe versus control). This analysis compares variables as polynomial functions rather than discrete values, thereby allowing us to evaluate entire movement patterns during the period of interest. This statistical approach can detect differences at any point throughout the entire stance phase, whereas using discrete values could lead to researchers not detecting existing differences if the differences do not happen precisely at the time of statistical evaluation.24 In addition, mixed-design repeated-measures functional data analysis of variance (2 × 2) was used to examine main effects and group-by-time interactions of the outcome variables, including sagittal- and frontal-plane kinematics and EMG amplitudes. All functional analyses were implemented using the fda package in RStudio (version 1.2.5033l; Posit Software, PBC). The independent t test was used to analyze patient characteristics between groups. Repeated-measures analyses of variance were used to examine pretest to posttest differences in the questionnaires between groups. The independent t test and repeated-measures analyses of variance were run using JMP Pro 14. An exploratory α level of .05 was used to determine differences in all comparisons.
RESULTS
We observed no differences in patient characteristics. No group-by-time interactions were found in the questionnaires.
Figure 2 shows lower extremity kinematics in the frontal plane. We observed a group-by-time interaction (P < .05) from 150 milliseconds before to 30 milliseconds after initial contact in the frontal-plane ankle angle. The strobe group had greater eversion angles from 150 milliseconds before to 30 milliseconds after the initial contact in the posttest than the pretest. However, we observed no pretest to posttest difference in frontal-plane ankle angles for the control group. No group-by-time interactions were found in the knee and hip angles for either group.
Citation: Journal of Athletic Training 59, 6; 10.4085/1062-6050-0605.22
Figure 3 shows lower extremity kinematics in the sagittal plane. We observed a group-by-time interaction (P < .05) from 30 to 130 milliseconds after initial contact in the sagittal-plane ankle angle. The strobe group had greater dorsiflexion angles from 30 to 96 milliseconds after initial contact in the posttest than in the pretest. However, we observed no pretest to posttest difference in the sagittal-plane ankle angles for the control group. No group-by-time interactions were found in the knee and hip angles for either group.
Citation: Journal of Athletic Training 59, 6; 10.4085/1062-6050-0605.22
Figure 4 shows EMG activations of 4 muscles in the lower extremity. We observed a group-by-time interaction (P < .05) from 60 to 150 milliseconds after initial contact in the TA. The strobe group had greater TA activation from 0 to 120 milliseconds after initial contact, whereas the control group had less TA activation from 80 to 150 milliseconds after initial contact in the posttest than in the pretest. Another group-by-time interaction (P < .05) was found from 10 to 90 milliseconds after initial contact in the PL. The strobe group had greater PL activation from 35 milliseconds before to 5 milliseconds after initial contact, whereas the control group had less PL activation from 25 to 90 milliseconds after initial contact in the posttest than in the pretest. We observed a group-by-time interaction (P < .05) from 15 to 80 milliseconds after initial contact in the Gmax. The strobe group had greater Gmax activation from 30 to 65 milliseconds after initial contact, whereas the control group had less Gmax activation from 90 to 135 milliseconds after initial contact in the posttest than in the pretest. We observed no group-by-time interaction in Gmed activation.
Citation: Journal of Athletic Training 59, 6; 10.4085/1062-6050-0605.22
DISCUSSION
The primary finding of this study was that the strobe group showed increased eversion and dorsiflexion angles along with increased TA and PL activation. The results suggest that a 4-week progressive rehabilitation with stroboscopic glasses was effective in altering neuromechanics during a single-legged drop landing. To our knowledge, we are the first to examine the effects of rehabilitation with stroboscopic glasses on movement biomechanics during a single-legged drop landing.
As we hypothesized, patients with CAI who underwent rehabilitation with stroboscopic glasses showed increased eversion and PL activation before initial contact during the drop-landing task. In other words, the strobe group showed “safer” preparatory neuromechanics in the posttest compared with the pretest, whereas the control group did not. The results suggest that the use of stroboscopic glasses during rehabilitation elicits positive changes in neuromechanics during a drop-landing task. In previous studies, researchers demonstrated that short-term exercise programs (4 and 6 weeks) using stroboscopic glasses were more beneficial in improving postural control during 1-legged standing in patients with CAI than the same programs without the glasses.8,14 These findings could be explained by 2 potential neurophysiological mechanisms. First, using stroboscopic glasses in rehabilitation could assist in inducing an adaptive neuroplastic response.15 In other words, neurophysiological changes after rehabilitation might have allowed the strobe group to prepare protective movements with adaptive neuroplastic responses.25 Second, rehabilitation with stroboscopic glasses could increase the use of sensory information arising from the somatosensory and vestibular systems rather than from visual input, visual-motor processing, or both.26 Based on the potential mechanisms of action, stroboscopic glasses may have enhanced preparatory neuromechanics by increasing weighting of somatosensory and vestibular inputs during a single-legged drop landing. However, none of these mechanisms were tested in our study, so our results cannot confirm these assumptions. The changes in neuromechanics for the strobe group could simply be due to increased concentration during the drop-landing task after the rehabilitation with limited visual input. Therefore, more studies need to be done to identify potential relationships between neuromechanics and neurophysiological changes after rehabilitation.
After initial contact, the strobe group showed changes in neuromechanics with increased dorsiflexion angle and TA and Gmax activation (30–96, 0–120, and 15–80 milliseconds after initial contact, respectively) in the posttest than in the pretest, whereas the control group demonstrated decreased TA and Gmax activation (80–150 and 90–135 milliseconds after initial contact, respectively). In a previous intervention study, researchers reported that individuals with CAI demonstrated reactive neuromuscular control of the leg muscles, such as the TA and PL, during single-legged drop landings after 6 weeks of hopping exercises.12 Minoonejad et al explained that repeated hopping during rehabilitation may increase muscle-spindle sensitivity and Golgi tendon organ inhibition, which enhance muscle elasticity and promote neuromuscular coordination.12,27 Furthermore, in previous studies, researchers reported that exercises with stroboscopic glasses could enhance sensorimotor control, as explained by the possible mechanisms mentioned in the preceding paragraph.8,14 Based on our results and previous findings, we assume that a 4-week training session with stroboscopic glasses may have led the strobe group to use mechanoreceptors in the leg more than the control group during rehabilitation, thereby providing beneficial muscle activation after initial contact. In addition, the participants in the strobe group may have trained themselves to land in a more flat-footed position (eg, increased dorsiflexion) during rehabilitation with visual disruption. Given that we are the first to study the effects of using stroboscopic glasses during rehabilitation on neuromechanics during a single-legged drop landing, we cannot provide definitive explanations of our results. Therefore, more data involving stroboscopic glasses during various movements are needed to confirm our assumptions.
Interestingly, the control group did not demonstrate differences in joint kinematics between the pretest and the posttest. This group even showed decreased muscle activation in the TA, PL, and Gmax after initial contact after rehabilitation. As mentioned previously, the control group included patients with CAI, but they did not use stroboscopic glasses during the rehabilitation. We expected the strobe group to show greater improvement in neuromechanics than the control group and expected the control group to show some neuromechanical improvements due to receiving rehabilitation. In an intervention study, Feger et al also reported decreased PL activation and plantar-flexion moment after rehabilitation, and these changes were considered a more efficient landing strategy.4 However, in other studies, researchers documented protective movement patterns, including increased eversion and dorsiflexion angle and PL activation, during a drop landing after rehabilitation for patients with CAI.11,12 This discrepancy could be explained in 2 ways. First, the type of rehabilitation could contribute to the discrepancy. In the previous studies, investigators used rehabilitation programs containing only hopping exercises (eg, figure-of-8 and zigzag pattern), whereas our rehabilitation program included both hopping and balance training. Second, the duration of rehabilitation could also contribute to the discrepancy. The duration of the previous rehabilitation programs was 6 weeks, whereas our program was 4 weeks. The duration of the rehabilitation program is the most significant variable responsible for improved neuromuscular function.28 Therefore, the hopping-intensive training and longer duration of the previous programs might have allowed patients with CAI greater degrees of freedom to alter their movements during a single-legged drop landing than our program did.
Our findings are important for clinicians in 2 ways. First, both our study and previous studies suggest that rehabilitation programs containing functional movements are effective in providing not only neurophysiological improvements, such as muscular strength and postural control, but also neuromechanical improvements during a single-legged drop landing.8–10 Thus, clinicians need to include functional movements during rehabilitation to improve neuromechanical functions in patients with CAI. Second, based on our results, the use of stroboscopic glasses during rehabilitation appears to help individuals with CAI prepare their movements with protective movement patterns, including increased eversion and dorsiflexion angles and TA and PL activations, during single-legged landings. Therefore, clinicians should consider using stroboscopic glasses when developing rehabilitative exercises for patients with CAI.
Our study had some limitations. First, we did not include follow-up testing after the posttest. Therefore, identifying how long the changes in movement patterns persist is difficult. Wright and Linens identified that patients with CAI had a smaller number of “giving way” episodes up to 6 months after a 4-week rehabilitation.29 However, the results of the previous study cannot be generalized to all other intervention studies. Therefore, more studies involving follow-up tests are needed to identify the long-term effects of rehabilitation on landing neuromechanics. Second, each exercise in the rehabilitation program has 7 levels of difficulty. As participants gained proficiency, environmental constraints were added to progressively increase the level of difficulty of the exercises. Therefore, the levels and amounts of exercises differed between participants based on their abilities to advance to the next level, which could influence the results of the study. Lastly, our findings can be generalized only to a physically active, college-aged population.
CONCLUSIONS
The primary finding of our study was that patients with CAI who underwent a 4-week rehabilitation with stroboscopic glasses demonstrated safer neuromechanics, including increased ankle-dorsiflexion and -eversion angles and TA and PL activation, during a single-legged drop landing. This finding suggests that using stroboscopic glasses during rehabilitation could help patients with CAI develop safe landing mechanics. To our knowledge, we are the first to study the use of stroboscopic glasses in a rehabilitation program to identify changes in movement patterns. Therefore, future studies are warranted to further develop the ideas presented in this study.
Study flowchart. All participants were assigned to either the strobe (n = 25) or the control (n = 25) group. Rehabilitation started within 7 days after the preintervention balance tests. Within 7 days after completing the intervention, participants performed the posttest in the same manner as the pretest. Abbreviations: ADL, Activities of Daily Living; FAAM, Foot and Ankle Ability Measure.
Lower extremity frontal-plane joint angles 150 milliseconds before and after initial contact during the single-legged drop landing: A, ankle angle; B, knee angle; and C, hip angle. Group-by-time interaction for D, ankle angle; E, knee angle; and F, hip angle. Pretest versus posttest differences in the strobe group for G, ankle angle; H, knee angle; and I, hip angle. Pretest versus posttest differences in the control group for J, ankle angle; K, knee angle; and L, hip angle. The 95% CIs (shaded gray area) are calculated for each data point. When 95% CIs did not cross zero, between-times values in each group were different. When no group-by-time interaction was found, group effects were not statistically meaningful. The y-axis in G through I and J through L represents the mean of differences in magnitudes between the pretest and posttest at each time. The y-axis in D through F represents differences in magnitudes between the graphs in G through I and J through L. a More eversion at posttest.
Lower extremity sagittal-plane joint angles 150 milliseconds before and after initial contact during the single-legged drop landing: A, ankle angle; B, knee angle; and C, hip angle. Group-by-time interaction for D, ankle angle; E, knee angle; and F, hip angle. Pretest versus posttest differences in the strobe group for G, ankle angle; H, knee angle; and I, hip angle. Pretest versus posttest differences in the control group for J, ankle angle; K, knee angle; and L, hip angle. The 95% CIs (shaded gray area) are calculated for each data point. When 95% CIs did not cross zero, between-times values in each group were different. When no group-by-time interaction was found, group effects were not statistically meaningful. The y-axis in G through I and J through L represents the mean of differences in magnitudes between the pretest and posttest at each time. The y-axis in D through F represents differences in magnitudes between the graphs in G through I and J through L. Abbreviations: DF, dorsiflexion; PF, plantarflexion. a More DF at posttest.
Electromyography activation of 4 lower extremity muscles 150 milliseconds before and after initial contact during the single-legged drop landing. A, Tibialis anterior. B, Peroneus longus. C, Gluteus medius. D, Gluteus maximus. Group-by-time interaction for E, tibialis anterior; F, peroneus longus; G, gluteus medius; and H, gluteus maximus. Pretest versus posttest differences in the strobe group for I, tibialis anterior; J, peroneus longus; K, gluteus medius; and L, gluteus maximus. Pretest versus posttest differences in the control group for M, tibialis anterior; N, peroneus longus; O, gluteus medius; and P, gluteus maximus. The 95% CIs (shaded gray area) are calculated by each data point. When 95% CIs did not cross zero, between-times values in each group were different. When no group-by-time interaction was found, group effects were not statistically meaningful. The y-axis in I through L and M through P represents the mean of differences in magnitudes between the pretest and posttest at each time. The y-axis in E through H represents differences in magnitudes between the graphs in I through L and M through P. a More muscle activation at posttest. b Less muscle activation at posttest.
Contributor Notes