This study will investigate the effects of ankle evertor muscle fatigue on gait stability during treadmill walking with mechanical perturbations. Participants will walk at two speeds (0.4 m/s and 1.0 m/s) while random medial and lateral perturbations (\<10% body weight) are applied to the pelvis. Surface EMG from ankle muscles and center of pressure (COP)-based gait parameters (e.g., step length, step width, single support duration, COP trajectory) will be analyzed before and immediately after an isotonic fatigue protocol of the ankle evertors.
The purpose of this study is to examine how ankle evertor muscle fatigue affects gait stability and neuromuscular responses during treadmill walking with mechanical perturbations. Perturbations will be applied randomly in the medial or lateral direction, but always shortly after initial foot contact, to specifically challenge ankle stabilization in stance. The study will include individuals with chronic ankle instability (CAI) and matched healthy controls. In the CAI group, the symptomatic side will be targeted with the fatigue protocol, whereas in healthy controls the tested side will be assigned to match the distribution of sprain laterality in the CAI group. Walking and perturbation protocol: Participants will first complete familiarization at 1.0 m/s, including both normal and perturbed walking. After familiarization, the measurements will consist of 2 minutes of unperturbed walking followed by 3 minutes of perturbed walking. The same procedure will then be repeated at 0.4 m/s, with familiarization (normal and perturbed walking) preceding the measurement block. The fatigue protocol will be applied immediately after these baseline blocks. Following fatigue, participants will immediately perform perturbed walking at 1.0 m/s. The fatigue protocol will then be repeated, followed by perturbed walking at 0.4 m/s. Fatigue protocol: Ankle evertor muscles will be fatigued using elastic resistance bands through repeated concentric and eccentric eversion contractions. The task will be paced using a metronome at a rate of one repetition per second, and will continue until the active eversion range of motion decreases by 50% compared to baseline.
Study Type
OBSERVATIONAL
Enrollment
40
The fatigue protocol will consist of repeated concentric-eccentric ankle eversion contractions against elastic resistance at a pace of one repetition per second, guided by a metronome, and performed in a seated position. Fatigue will be defined as a clear inability to perform the full range of eversion, i.e. the range of motion falling below 50% of the initial value despite evident effort by the participant.
University Rehabilitation Institute Republic of Slovenia - URI Soča
Ljubljana, Slovenia
RECRUITINGSurface EMG root mean square (RMS) amplitude of ankle muscles
Surface EMG RMS amplitude from peroneus longus (PL), tibialis anterior (TA), soleus (SOL), gastrocnemius medialis (GM), and gluteus medius (GMed), recorded bilaterally during treadmill walking. EMG will be time-normalized to the gait cycle (0-100%). The primary epoch is the perturbation step (shortly after initial contact through stance). For each muscle and speed, EMG during perturbed walking will be normalized to matched unperturbed walking.
Time frame: Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Center of Pressure mediolateral displacement (COPx)
Mediolateral displacement of the center of pressure (COPx) during walking, time-normalized to the gait cycle (0-100%). In addition, COPx will be expressed relative to the sacral marker (COPx-SACRx). Values will be presented in absolute units (cm) and compared between matched perturbed steps at the same walking speed (before and after fatigue).
Time frame: Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Step Length and width
Step length (heel-to-heel) and step width of the perturbation step, derived from 3D motion capture with reflective markers placed on anatomical landmarks. Both parameters will be compared against matched unperturbed steps.
Time frame: Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
Ground reaction forces (GRF)
Vertical GRF (Fz; peak, mean, loading rate), with optional analysis of anteroposterior (Fy) and mediolateral (Fx) components, time-normalized to the gait cycle (0-100%). Values reported in absolute units (N for forces; N/s for loading rate).
Time frame: Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).
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Ratings of perceived exertion
Description: Ratings of perceived exertion (RPE) will be assessed at the end of each fatigue protocol using the Borg 10 category-ratio scale, with 0 is no effort and 10 is an extreme physical effort.
Time frame: Baseline (Day 1, prior to fatigue protocol) and immediately post-fatigue (Day 1, within 5 minutes after fatigue protocol).