During TLM, fatigue may occur quick

During TLM, fatigue may occur quickly. A previous study reported that fatiguecan be caused by many different mechanisms, ranging from the accumulation of metabolites within muscle fibers to the generation of an inadequate motor command in the motor cortex 18. The power spectrum of the EMG frequency shifts toward the lower band during prolonged muscle contraction 19-21. The shift of the spectrum toward the lower band is caused by a decrease in muscle fiber conduction velocity. This phenomenon is used to estimate localized muscular fatigue. Furthermore, as well as changes in power spectrum of the EMG signal, increases in EMG amplitude have been observed and may be caused by recruitment of motor units compensating for fatigued motor units exhibiting reduced muscle fiber conduction velocities 22. Therefore, examining changes in the amplitude and power frequency of EMG signals during TLM could be useful for evaluating muscle load.