Stair Biomechanics and Vibration Study After ACLR

Individuals with ACLR commonly show altered lower extremity biomechanics and quadriceps dysfunction that may contribute to the development of knee osteoarthritis. Stair negotiation places greater demands on the knee than level walking, yet findings on stair biomechanics after ACLR are inconsistent. Whole-body vibration (WBV) and local muscle vibration (LMV) acutely improve quadriceps function and gait biomechanics after ACLR, but their effects on stair biomechanics are unknown. Aims: 1. to compare lower extremity biomechanics during gait, stair ascent, and stair descent between individuals 1 to 3 years after ACLR and matched healthy controls; 2. to determine inter-limb differences in biomechanics during gait and stair negotiation within individuals with ACLR; 3. to evaluate the acute effects of WBV and LMV on stair ascent and descent biomechanics in individuals with ACLR compared with a control condition. Design: a case-control comparison nested within a single-blind, repeated-measures crossover design. ACLR participants complete three visits separated by at least 48 hours. Visit 1 is a baseline session with stair biomechanics assessed before and after a control condition (no vibration), plus gait biomechanics, isometric quadriceps and hamstring strength, single-leg and triple hop tests, and patient-reported outcomes. At visits 2 and 3, participants receive WBV and LMV in counterbalanced order, with stair biomechanics assessed immediately before and after the intervention. For all conditions, participants hold a squatted position (approximately 60 degrees of knee flexion) for 1 minute, repeated 6 times with 2 minutes of rest. WBV is delivered via a vibrating platform (30 Hz, 2 g). The control condition uses the same posture and timing without vibration. Healthy controls complete one visit identical to ACLR visit 1. Biomechanics are collected with 3D motion capture synchronized with force plates under the second and third steps of an instrumented staircase. The data collector and outcome assessor are blinded to the vibration condition, which is administered by a separate research assistant.