Influence of Support Surface Stability on Changes in Quadriceps Femoris Muscle Thickness During Progressive Squat Exercise in Patients with Stroke: A Randomized Controlled Trial

Background and Objectives: Stroke, a neurological disorder caused by damage to the central nervous system, is commonly accompanied by impairments in motor and sensory function and muscle strength. We compared the effects of progressive squat exercises performed under varying support-surface stability conditions on quadriceps femoris muscle thickness in patients 6 months to less than 1 year after stroke, using rehabilitative ultrasound imaging. Materials and Methods: This randomized, open-label, parallel-group controlled trial assessed 36 patients with stroke for eligibility. Four individuals were excluded before randomization; the remaining 32 participants were randomly assigned in a 1:1 ratio to either the unstable-support-surface squat exercise group (n = 16) or the stable-support-surface squat exercise group (n = 16). Both groups performed progressive squat exercises five times per week for 4 weeks. Quadriceps femoris muscle thickness was measured before and after the intervention using rehabilitative ultrasound imaging. Results: Between-group comparisons of changes from baseline showed significantly greater increases in rectus femoris and vastus medialis muscle thickness in the unstable support-surface squat exercise group than in the stable support-surface squat exercise group (p < 0.05). No significant between-group differences were observed in vastus intermedius or vastus lateralis muscle thickness (p > 0.05). Conclusions: Progressive squat exercise performed on an unstable support surface resulted in greater increases in rectus femoris and vastus medialis muscle thickness than the same exercise performed on a stable support surface. However, these findings are limited to muscle thickness and should not be interpreted as evidence of improved muscle strength or functional performance.