Evaluating the Intensity of Muscle Contraction by Near-Infrared Spectroscopy, a Potential Application for Scaling Muscle Spasm

Muscle spasticity, common in conditions such as cerebral palsy, spinal cord injury, and multiple sclerosis, is traditionally assessed using the Modified Ashworth Scale, which lacks consistency. This study evaluates near-infrared spectroscopy (NIRS) as a non-invasive tool for measuring muscle contraction intensity. Thirty-seven healthy adults performed isometric contractions at varying intensities (15%, 30%, 45%, and 60% of maximal voluntary contraction), with NIRS sensors monitoring changes in the Tissue Oxygenation Index (TOI) and electromyography (EMG) measuring muscle activity. Results demonstrated a significant negative correlation between contraction intensity and ΔTOI, indicating that higher contraction levels resulted in greater reductions in muscle oxygenation. Additionally, a multinomial logistic regression model confirmed that TOI could reliably predict contraction intensity (p < 0.001). This technique could provide real-time, objective data for spasticity assessment, potentially improving treatment plans.