Effects of Lunge Exercise with Reformer on Muscle Activation, Balance, and Knee Deviation in Young Adults with Chronic Ankle Instability

Objective: This study aimed to evaluate the effects of spring resistance levels during reformer lunge exercises on muscle activation, balance, and knee deviation in adults with Chronic Ankle Instability (CAI). This study also aimed to identify the optimal resistance level for functional recovery. Design: A repeated measures design was followed. Methods: Twenty-one university students with ankle instability instrument scores of ≥5 were selected to participate in the study. Participants performed lunge exercises on a reformer using randomized spring resistance levels (None, Yellow, Blue). Muscle activity was measured using surface electromyography, balance was assessed using a Wii balance board, and knee deviation was analyzed using an inertial measurement unit sensor. Each trial consisted of 10-second recordings after reaching a 60° hip and 90° knee position, with standardized movement speed controlled by a metronome. Data were collected across three trials per condition with rest intervals between trials. Results: Under the blue spring condition, activation of the gluteus medius and rectus femoris significantly increased (p<0.05), whereas sway velocity and sway distance were significantly reduced (p < 0.05). Changes in spring resistance did not significantly affect knee deviation (p>0.05). Conclusions: Adjusting the reformer spring resistance affects muscle activation and balance in adults with CAI, with the highest resistance (blue spring) yielding the most pronounced improvements. These findings suggest that the Pilates reformer, particularly with tailored resistance levels, is an effective tool for the rehabilitation and prevention of recurrence in patients with CAI.