Quantifying Lower-Limb Muscle Coordination During Cycling Using Electromyography-Informed Muscle Synergies

Assessment of muscle coordination during cycling can provide insight into motor control strategies and movement efficiency. This study evaluated muscle synergy patterns as indicators of neuromuscular coordination in the lower limbs across three power levels of cycling (LPL = Lowest Power Level, MPL = Middle Power Level, HPL = Highest Power Level).

Twenty recreational cyclists performed a graded cycling test on a stationary bicycle ergometer. Electromyography (EMG) was recorded bilaterally from seven lower-limb muscles and muscle synergies were extracted using non-negative matrix factorization. The Synergy Index (SI) and Synergy Coordination Index (SCI) were calculated to assess muscle coordination patterns.

Four muscle synergies were identified consistently across power levels, with changes in synergy composition and activation timing correlated with increasing muscular demands. At the dominant hip, SI remained consistent across power levels (0.50 ± 0.11 at LPL, 0.56 ± 0.15 at MPL, 0.54 ± 0.15 at HPL). At the dominant knee, SI decreased with increasing power (0.47 ± 0.07 at LPL to 0.34 ± 0.05 at HPL; p < 0.01, η_p² = 0.51). At the dominant ankle, SI increased with increasing power (0.19 ± 0.09 at LPL to 0.27 ± 0.10 at HPL; p < 0.01, η_p² = 0.41). The SCI increased with increasing power level (0.08 ± 0.04 at LPL, 0.13 ± 0.08 at MPL, 0.24 ± 0.11 at HPL; p < 0.01, Kendall's W = 0.59).

These findings provide insight into how the central nervous system modulates its response to increasing mechanical demands. Combining synergy indices offers a promising approach to assess motor control, inform rehabilitation, and optimize performance in cycling tasks.