Abstract
In Paralympic sit-skiing, propulsive efficacy and postural control depend heavily on upper body motor unit recruitment and force output regulation, particularly when navigating varying terrain gradients. This study investigated motor unit recruitment patterns and force setting accuracy in twelve elite Paralympic sit-skiers (LW10–LW12 classifications) across three treadmill slope gradients (5%, 10%, and 15%). High-density surface electromyography (sEMG) was recorded from the rectus abdominis, erector spinae, latissimus dorsi, and triceps brachii, while custom force-instrumented poles and trunk inertial measurement units assessed force profiles and kinematic stability. Results revealed that steeper gradients significantly increased sEMG root mean square amplitude across all muscle groups (p < 0.001), with a pronounced shift in mean power frequency indicating rapid neuromuscular fatigue in trunk stabilizers among athletes with higher spinal cord lesions (LW10–LW10.5). Force setting accuracy, measured via peak force variability and target force profile error, degraded by 24.6% on the 15% incline compared to the 5% incline. Furthermore, trunk anterior-posterior range of motion decreased on steeper slopes, constraining the double-poling stroke length. These findings demonstrate that steep inclines place a dual constraint on neuromuscular control, compromising force setting accuracy while accelerating local muscle fatigue. Practical applications include refining adaptive seating configurations and implementing target-force biofeedback training to optimize propulsion and prevent overuse injuries in Para-skiing.
