Correlation of average muscle fiber conduction velocity measured during cycling exercise with myosin heavy chain composition, lactate threshold, and VO2max

The aim of the study was to investigate the correlation between myosin heavy chain (MHC) composition, lactate threshold (LT), maximal oxygen uptake VO2max, and average muscle fiber conduction velocity (MFCV) measured from surface electromyographic (EMG) signals during cycling exercise. Ten healthy male subjects participated in the study. MHC isoforms were identified from a sample of the vastus lateralis muscle and characterized as type I, IIA, and IIX. At least three days after a measure of LT and VO2max, the subjects performed a 2-min cycling exercise at 90 revolutions per minute and power output corresponding to LT, during which surface EMG signals were recorded from the vastus lateralis muscle with an adhesive electrode array. MFCV and instantaneous mean power spectral frequency of the surface EMG were estimated at the maximal instantaneous knee angular speed. Output power corresponding to LT and VO2max were correlated with percentage of MHC I (R2 = 0.77; and 0.42, respectively; P < 0.05). MFCV was positively correlated with percentage of MHC I, power corresponding to LT and to VO2max (R2 = 0.84; 0.74; 0.53, respectively; P < 0.05). Instantaneous mean power spectral frequency was not correlated with any of these variables or with MFCV, thus questioning the use of surface EMG spectral analysis for indirect estimation of MFCV in dynamic contractions.