Effects of a 30-Minute Run on Accelerometry-Derived Mechanical Load and Gastrocnemius Surface EMG

This study analyzed whether the change in mechanical load during a moderate intensity run, measured with accelerometers, could be explained by neuromuscular fatigue, assessed with surface electromyography (sEMG). Twenty-eight amateur runners completed a 30-min treadmill run, and acceleration spikes at the ankles, tibias and sacrum were recorded with high-g accelerometers. Gastrocnemius sEMG was measured during maximal voluntary isometric contractions before and after the run. Right tibial spikes increased from 81.7 to 88.7 m·s−2 (p = 0.009), whereas ankle and sacral spikes remained stable (p > 0.05). Step time and cadence were also constant (about 362 ms and 158 steps per minute; p > 0.05). The limb × sector interaction showed that inter-limb asymmetry became more pronounced over the run, favoring the right side at the tibia (β = 0.127 m·s−2 per sector; pFDR = 0.042) and the sacrum (β = 0.062; pFDR = 0.034), but not at the ankle (p = 0.731). This localized mechanical drift in the knee and sacral region, rather than at the ankle, warrants further investigation. Neither the power spectral density nor sEMG amplitude differed between pre- and post-run (p > 0.05). Mechanical load drifted toward the right limb without clear electromyographic signs of gastrocnemius fatigue.