Although tongue pressure did not ex

Although tongue pressure did not exhibit temporal changes between the stages during 7-s TLM, both S-hyo and I-hyo EMG activities increased from the Early to Late stages, and a significant difference was observed in area of I-hyo EMG burst in the Post TLM period. On the other hand, the mean power frequency of EMG burst in the S-hyo and I-hyo muscles were significantly decreased in the Late compared with Early stages both during the Ant and Post TLM periods. Previous morphological and histochemical studies demonstrated that the intrinsic tongue muscles arecomposed of less than 25% slow type I and more than 75% fast II type fibers in cats 34. This pattern is similar in humans, and has been immunohistochemically quantifiedwith the myosin heavy chain method 35. Increase of EMG amplitude and decrease of power frequency of EMG burst are considered to be signs of muscle fatigue 19-21. We suspect that the fast and fatigable muscles, such as the tongue muscles, were first recruited when tongue exercise strength intensity increased, and S-hyo and I-hyo muscles could contribute to compensating intrinsic tongue muscle fatigue to maintain tongue pressure in the late stages of the 7-s TLM task. Comparing EMG patterns between the two stages (early vs late) revealed a decrease in the mean power frequency of I-hyo EMG burst, while the area of I-hyo EMG burst was not affected in the posterior TLM. Although we do not have direct evidence, these results suggestthat I-hyo muscle fatigue may have affected the power frequency but not the amplitude.Analysis in temporal change during measurement time