Non-invasive Assessment Of Muscle Fibre Conduction Velocity During An Incremental Maximal Cycling Test

Abstract

Muscle fibre conduction velocity (MFCV) can provide information about motor units recruitment strategies. Recently, MFCV has been measured, non invasively, during constant-load sub-maximal cycling exercise and was found to correlate positively with % of type I myosin heavy chain. PURPOSE: The present study aimed at verifying the hypothesis that MFCV, measured during an incremental cycling test using surface electromyography (sEMG), could be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (Tvent), VO2max and MFCV was explored. METHODS: Eight male subjects (28±4 yrs) undertook a one-minute incremental cycling test to exhaustion. In order to measure Tvent and VO2max an open circuit breath by breath gas analyzer (Quark b2 Cosmed, Italy) was used., The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed over 250ms epochs overlapped to one another by half their length. RESULTS: The mean VO2max obtained during the maximal test was 46.5±3.5ml*kg-1*min-1, and the Tvent was reached at 65.5±5.4% of VO2max. In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.3±0. 3m*s-1 at an intensity corresponding to the Tvent. Thereafter, MFCV declined until maximal work intensities. MFCV was positively related to the mechanical work both at VO2max (R2=0.69 P<0.05) and particularly at Tvent occurrence (R2=0.9; P<0.01). CONCLUSIONS: This study demonstrates that MFCV can be used as non invasive tool to infer motor unit recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities.