Correlation between surface electromyogram, oxygen uptake and blood lactate concentration during dynamic leg exercises

Very few data are found in the literature on the adjustment of the motor drive to contracting muscles to their oxygen uptake (V(O2)). The present study examines in seven untrained and trained individuals, who performed a progressive 8 min and two 5 min constant-load cycling exercises, the changes in the ratio between total EMG energy (root mean square or RMS), recorded in a leg extensor (vastus lateralis), to the corresponding V(O2) value and their correlations with the anaerobic threshold (V(O2)AT) and the peak blood lactate concentration. In all circumstances, the RMS/V(O2) ratio began to increase, then it decreased progressively despite V(O2) continued to rise (progressive exercise) or plateaued (constant-load exercises preseted at a sub- or suprathreshold level). The decrease in RMS/V(O2) ratio persisted and it was often accentuated during the first 2 min of the recovery period. In all exercise protocols, the rate of RMS/V(O2) decrease was positively correlated with the initial peak increase in this ratio. During progressive exercise, the peak increase in RMS/V(O2) ratio as well as its rate of decrease were negatively correlated with V(O2)AT. Thus, training and/or the reduction of anaerobic muscle metabolism attenuate the changes in RMS/V(O2) ratio. During constant-load exercise trials, the rate of decrease in RMS/V(O2) ratio was positively correlated with the plateau V(O2) value and also the peak blood lactate concentration. This suggests that information on the magnitude of the anaerobic muscle metabolism play a key role in the mechanisms which adjust RMS to V(O2).