Sport Specific Differences in Upper Limb Median Frequency Responses During Isometric Push and Pull Tasks in Volleyball and Fitness Athletes

Purpose: To compare sport-specific differences in upper-limb muscle fatigue characteristics, assessed via surface EMG median frequency (MF), during brief isometric push and pull tasks performed in seated and standing postures. Methods: Thirty-six athletes (volleyball, n=18; fitness, n=18) performed 20-s isometric contractions in four conditions (seated upright row, seated shoulder press, standing upright row, standing shoulder press) using both dominant and non-dominant limbs. Surface EMG was recorded bilaterally from the biceps brachii, triceps brachii, deltoid, and trapezius. MF was calculated using Welch’s method from a steady-state window (5-15 s of the 20-s contraction) to avoid onset and end-of-trial transients and expressed in Hz. Linear mixed-effects models tested the effects of group, posture, action, and side. Results: MF was higher during the upright row than the shoulder press for the biceps, deltoid, and trapezius (p<0.001; within-subject dz=0.59–1.02). For the triceps, significant effects of group (p=0.019), posture (p=0.026), and a group×posture interaction (p=0.019) were observed, with fitness athletes showing higher MF than volleyball athletes particularly in the seated condition. No robust main effects or interactions involving side were detected. Conclusion: In these brief isometric tasks, MF responses were predominantly task-dependent (pull>push) for biceps, deltoid, and trapezius, whereas triceps MF showed sport- and posture-dependent modulation. These findings support the use of task-specific EMG spectral outcomes to probe fatigue-related neuromuscular characteristics across athletic populations.