Jaw Clenching Alters Neuromuscular Coordination in Dynamic Postural Tasks: A Pilot Study on Single-Leg Sit-to-Stand Movements

<b>Background/Objective:</b> Postural stability and motor coordination require precise regulation of agonist and antagonist muscle activities. Jaw clenching modulates neuromuscular control during static and reactive postural tasks. However, its effects on dynamic voluntary movement remain unclear. This pilot study aimed to investigate the effects of jaw clenching on muscle activity and kinematics during repetitive single-leg sit-to-stand task performance. <b>Methods:</b> Eleven healthy adults (age: 21.2 ± 0.4 years; 6 males and 5 females; height: 167.9 ± 9.6 cm; body weight: 59.7 ± 8.1 kg) performed repetitive single-leg sit-to-stand tasks for 30 s under jaw-clenching and control conditions. Electromyography (EMG) signals from eight muscles and kinematic data from 16 inertial measurement unit sensors were analyzed, focusing on the seat-off phase. <b>Results:</b> Jaw clenching resulted in a significantly lower success rate than the control condition (success rate: 0.96 ± 0.13 vs. 0.78 ± 0.29, <i>p</i> = 0.047). Under the jaw clenching condition, failed trials exhibited higher medial gastrocnemius and masseter EMG activity (<i>p</i> < 0.001), lower erector spinae longus EMG activity (<i>p</i> < 0.001), and altered kinematics, including increased trunk yaw and roll angles (<i>p</i> < 0.001). Jaw clenching increased the coactivation of the gastrocnemius and tibialis anterior muscles (<i>p</i> < 0.001), disrupting the reciprocal muscle patterns critical for task performance. <b>Conclusions:</b> These findings suggest that jaw clenching may reduce task performance by altering neuromuscular coordination during dynamic postural tasks.