Reproducibility and validity of the quadriceps muscle integrated electromyogram threshold during incremental cycle ergometry.

The principle aims of this research were, firstly, to determine if the relationship between integrated electromyography (iEMG) and exercise intensity was linear or threshold-like, and secondly, to determine if the relationship between iEMG and exercise intensity was repeatable on different test occasions. A group of 20 trained male subjects participated in the study. Each subject completed two incremental exercise tests on a Monark cycle ergometer. The tests were identical and separated from each other by a mean period of 42 (SD 12) h. The EMG signals were recorded from the vastus lateralis, rectus femoris and vastus medialis muscles at each intensity using surface electrodes. The relationship between iEMG and intensity was shown to be linear (r = 0.95 to r = 0.98) with no obvious iEMG thresholds present. The gradients of simple regression lines fitted to the iEMG compared to intensity were not significantly different on the retest occasion (CV 9%-12%). In summary, the findings of this study indicated that, during incremental exercise, the relationship between iEMG of the quadriceps musculature and exercise intensity was linear and not threshold-like. Furthermore, the linear relationship between iEMG and workload was repeatable on different test occasions.