Effect of power, pedal rate, and force on average muscle fiber conduction velocity during cycling

1 Center for Sensory-Motor Interaction, Aalborg University, DK-9100 Aalborg, Denmark; 2 Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica, Politecnico di Torino, Torino, 10129 Italy; and 3 Department of Applied Physiology, University of Strathclyde, Glasgow G13 1PP, United Kingdom Submitted 14 June 2004 ; accepted in final form 27 July 2004 Muscle fiber conduction velocity (MFCV) provides indications on motor unit recruitment strategies due to the relation between conduction velocity and fiber diameter. The aim of this study was to investigate MFCV of thigh muscles during cycling at varying power outputs, pedal rates, and external forces. Twelve healthy male participants aged between 19 and 30 yr cycled on an electronically braked ergometer at 45, 60, 90, and 120 rpm. For each pedal rate, subjects performed two exercise intensities, one at an external power output corresponding to the previously determined lactate threshold (100% LT) and the other at half of this power output (50% LT). Surface electromyogram signals were detected during cycling from vastus lateralis and medialis muscles with linear adhesive arrays of eight electrodes. In both muscles, MFCV was higher at 100% LT compared with 50% LT for all average pedal rates except 120 rpm (mean ± SE, 4.98 ± 0.19 vs. 4.49 ± 0.18 m/s; P < 0.001). In all conditions, MFVC increased with increasing instantaneous knee angular speed (from 4.14 ± 0.16 to 5.08 ± 0.13 m/s in the range of instantaneous angular speeds investigated; P < 0.001). When MFCV was compared at the same external force production (i.e., 90 rpm/100% LT vs. 45 rpm/50% LT, and 120 rpm/100% LT vs. 60 rpm/50% LT), MFCV was higher at the faster pedal rate (5.02 ± 0.17 vs. 4.64 ± 0.12 m/s, and 4.92 ± 0.19 vs. 4.49 ± 0.11 m/s, respectively; P < 0.05) due to the increase in inertial power required to accelerate the limbs. It was concluded that, during repetitive dynamic movements, MFCV increases with the external force developed, instantaneous knee angular speed, and average pedal rate, indicating progressive recruitment of large, high conduction velocity motor units with increasing muscle force. dynamic exercise; surface electromyogram; electrode arrays Address for reprint requests and other correspondence: D. Farina, Center for Sensory Motor Interaction, Aalborg University, Fredrik Bajers Vej 7 D-3, DK-9100 Aalborg, Denmark (E-mail: df{at}hst.aau.dk )