Sport specific differences in upper limb median frequency responses during isometric push and pull tasks in volleyball and fitness athletes

To compare sport-specific differences in upper-limb EMG median frequency (MF) responses during brief isometric push and pull tasks performed in seated and standing postures. 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 (LMM) were used to test the effects of group, posture, action, and side. 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. 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 compare neuromuscular characteristics across athletic populations.