Electromyographic activity related to aerobic and anaerobic threshold in ergometer bicycling

Electromyographic activity (EMG) of the knee extensor musculature (m. vastus lateralis, m. vastus medialis, m. rectus femoris), triceps surae (m. gastrocnemius, m. soleus) and m. tibialis anterior was studied in ergometer bicycling at five different power outputs around aerobic (AerT) and anaerobic (AnT) thresholds. EMGs were sampled with surface electrodes for ten revolutions at the beginning, in the middle and at the end of each work load and integrated (IEMG) separately for each of the muscles and for the descending (work) and ascending (rest) phase of the revolution. The mean power frequency (MPF) of the power spectral density function for the descending periods was also calculated. The first work load was 50% of the maximal load, the second at the level of AerT, the third at the AnT, the fourth between the AnT and the maximal load and the fifth load was maximal. The AerT and AnT were determined using blood lactate, ventilation volume and oxygen consumption. Five males from 21 to 38 years of age volunteered as subjects. When the IEMGs of the knee extensor and triceps surae musculature were related to the work load a nonlinearity was found at the aerobic threshold while no further change in the linearity was found at the AnT. The non-linear increase of the IEMG at the AerT was found both for the working (descending) and resting (ascending) phases of the cycling. In the MPF no difference below and above the AnT was found. It was thought that the integral of EMG activity could serve as an indicator of the aerobic threshold of an individual muscle.