Muscle fibre conduction velocity and cardiorespiratory response during incremental cycling exercise in young and older individuals with different training status

We investigated the effect of ageing and training on muscle fibre conduction velocity (MFCV) and cardiorespiratory response during incremental cycling exercise. Eight young (YT; 24±5 yrs) and eight older (OT; 64±3 yrs) cyclists, together with eight young (YU; 27±4 yrs) and eight older (OU; 63±2 yrs) untrained individuals underwent to an incremental maximal test on a cycle ergometer. Ventilatory threshold (VT), respiratory compensation point (RCP) and maximal oxygen uptake (VO2max) were identified and MFCV recorded from the vastus lateralis muscle using surface electromyography with linear arrays electrodes.

In YT MFCV increased with the exercise intensity, reaching a peak of 4.99±1.02 [m/s] at VT. Thereafter, and up to VO2max, MFCV declined. In YU MFCV showed a similar trend although the peak [4.55±0.53m/s] was observed, at 75% of VO2max an intensity higher than VT (66% of VO2max). In both YT and YU MFCV did not decline until RPC, which occurred at 78% VO2max in YU and at 92% VO2max (P<0.01) in YT. Differently from young individuals, MFCV in older subjects did not increase with exercise intensity. Moreover, maximal MFCV in OU was significantly lower [3.53±0.40m/s;] than that of YT (P<0.005) and YU (P<0.05).

The present study shows that, especially in young individuals, MFCV reflects cardiorespiratory response during incremental dynamic cyclic exercise and hence can be used to investigate motor unit recruitment strategies.