Non-Uniform Changes in Muscle Fiber Conduction Velocity during Sustained Isometric Contraction of the Vastus Medialis Muscle

Muscle fiber conduction velocity (MFCV) decreases during sustained fatiguing contraction due to metabolic accumulation. Differences in morphological and architectural characteristics of muscle fibers within the vastus medialis muscle may result in non-uniform metabolites accumulation and as consequence non-uniform changes in fiber conduction velocity. The aim of this study was to assess muscle fiber conduction velocity at the level of single motor unit in different locations of the vastus medialis muscle during sustained contraction. Surface and intramuscular EMG signals were recorded from two locations of the right vastus medialis muscle of ten healthy men during 70s isometric contraction at 20% of the maximal force. The distal location of the vastus medialis muscle resulted in a larger value of conduction velocity (p < 0.05) and greater conduction velocity rate of reduction (p < 0.05) during sustained contraction compared with the proximal region. These results indicated a non-uniform change in electrophysiological membrane properties at different locations of the vastus medialis muscle during sustained contraction.