Higher muscle fiber conduction velocity and early rate of torque development in chronically strength trained individuals

Strength trained individuals (ST) develop greater levels of force when compared to untrained subjects. These differences are partly of neural origin and can be explained by training induced changes in the neural drive to the muscles. In the present study we hypothesize a greater rate of torque development (RTD) and faster recruitment of motor units with greater muscle fiber conduction velocity (MFCV) in ST when compared to a control cohort. MFCV was assessed during maximal voluntary isometric explosive contractions of the elbow flexors in eight ST and eight control individuals. MFCV was estimated from high-density surface electromyogram recordings (128 electrodes) in intervals of 50 ms starting from the onset of the EMG. The rate of torque development (RTD) and MFCV were computed and normalized to their maximal voluntary torque (MVT) values. The explosive torque of the ST was greater than in the control group in all time intervals analyzed (p<0.001). The absolute MFCV values were also greater for the ST than controls at all time intervals (p<0.001). ST also achieved greater normalized RTD in the first 50 ms of contraction (887.6 ± 152 vs. 568.5 ± 148.66 %MVT∙s-1, p<0.001) and normalized MFCV before the rise in force when compared to controls. We have shown for the first time that ST can recruit motor units with greater MFCV in a shorter amount of time when compared to untrained subjects during maximal voluntary isometric explosive contractions.