Analysis of sEMG Amplitude Temporal Change During Low-Intensity Sustained Muscle Contraction

Abstract

Abstract:

Context:

Surface electromyography (sEMG) is widely used to evaluate muscle fatigue; however, conventional indices such as amplitude and frequency parameters may not sensitively detect early changes in motor unit recruitment during low-intensity sustained contractions.

Aims:

This study aimed to determine the timing and characteristics of temporal changes in muscle action potentials during sustained low-intensity isometric contraction, focusing on detailed waveform analysis including amplitude probability distribution function (APDF).

Settings and Design:

An experimental laboratory study was conducted with healthy young adults performing sustained isometric elbow flexion at a submaximal load until task failure.

Methods and Material:

              Seventeen healthy adults maintained isometric elbow flexion at 25% of their maximum voluntary isometric contraction (MVIC) of the biceps brachii until they could not sustain the target torque for 5 s. sEMG signals from the dominant biceps brachii were divided into 11 equal intervals. Average amplitude, median frequency, zero-crossing rate, turn amplitude, kurtosis, skewness, and APDF across amplitude bands (0–100% peak) were calculated for each interval.

Statistical analysis used:

              Temporal changes were assessed using repeated-measures ANOVA followed by Dunnett’s post hoc tests (α = 0.05).

Results:

              Mean endurance time was 680.3 ± 180.5 s. Mean amplitude increased from the 40% interval, while median frequency, zero-crossing rate, and turn amplitude decreased from the 90% interval. APDF showed early decreases in low-amplitude bands (0–5% peak) and gradual increases in higher bands from the 10% interval.

Conclusions:

              Motor unit recruitment adjustments begin early during sustained low-intensity contraction. APDF demonstrated greater sensitivity to early temporal changes than conventional sEMG indices.