Decoding Resting Muscle Activity: Preliminary Insights into Upper Limb Neuromuscular Health

Objectives. Resting-state electromyography (EMG) is underexplored compared to maximal muscle activity but provides valuable insights into baseline neuromuscular health. Minimal EMG activity reveals patterns of muscle fatigue, recovery, and dysfunction, aiding in the detection of work-related upper limb disorders (WRULDs).
Materials and Methods. Resting-state and maximal effort EMG data, including voltage and spectral mean, were collected from 23 healthy participants across six upper limb muscle groups: deltoids, biceps, triceps, brachioradialis, wrist flexors, and extensors. Data analysis focused on asymmetry, variability, and inter-muscle correlations using IBM SPSS Statistics 28.
Results. The lowest resting-state spectral mean was in the right deltoids (128.18 ± 35.32 Hz), while the highest was in the right biceps (188.72 ± 30.20 Hz). The highest maximal spectral mean occurred in the right extensors (157.93 ± 21.85 Hz). The biceps exhibited the greatest right-side dominance (ratio: 1.214, 21.41% stronger), followed by the triceps (1.159, 15.91% stronger) and brachioradialis (1.125, 12.48% stronger). Conversely, the wrist flexors showed left-side dominance, with the right side 18.62% weaker (ratio: 0.814). The deltoids were nearly symmetrical (0.991, 0.90% weaker on the right). Stable activation patterns were observed in the deltoids (CV: 0.51), while the brachioradialis displayed moderate variability (SD: 0.98). Significant correlations included the right deltoid with the right biceps (r = 0.54, p = 0.0078) and the right brachioradialis with wrist flexors (r = 0.71, p=0.0001).
Conclusions. The biceps and brachioradialis emerged as key muscles for further study due to their high activation, asymmetry, and inter-muscle correlations. Resting-state EMG shows potential in diagnosing neuromuscular imbalances and guiding interventions for WRULDs. Findings suggest that repetitive occupational tasks may exacerbate imbalances, highlighting the need for ergonomic designs and targeted rehabilitation protocols.