{'fraction_non_alphanumeric': 0.04233983286908078, 'fraction_numerical': 0.012256267409470752, 'mean_word_length': 4.888524590163934, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Association between knee extensor strength and EMG activities during squat movement.

PURPOSE
The present study aimed to clarify how the force-generating capability of quadriceps femoris (QF) is associated to its surface EMG activity during a body mass-based squat movement.


METHODS
Isometric knee extension torque (KET) during maximal voluntary contraction and EMG activities of the rectus femoris and vastus lateralis muscles during a body mass-based squat movement were determined in 53 men and 48 women age 19-90 yr, including 18 frail elderly persons who used the long-term care insurance system. The rectified EMG signals during the squat movement were averaged and normalized as the relative value (%EMG(max)) to that during maximal voluntary contraction. The %EMG(max) values for rectus femoris and vastus lateralis were averaged and used as an index representing the level of muscular activities of QF during the squat movement (QF %EMG(max)).


RESULTS
QF %EMG(max) was nonlinearly related to KET relative to body mass (KET/BM). Linear piecewise continuous regression analysis showed that there was a breakpoint of 1.9 N·m·kg(-1) in the relationship between the two variables. In individuals with KET/BM less than 1.9 N·m·kg(-1), QF %EMG(max) rapidly increased as KET/BM decreased.


CONCLUSIONS
The current results indicate that the activity level of QF during a body mass-based squat movement is influenced by its force generation capability. For individuals with a KET/BM less than 1.9 N·m·kg(-1), body mass-based squat movement is considered to be a fairly high-intensity exercise. The breakpoint of 1.9 N·m·kg(-1) may be assumed to be a threshold level of knee extensor strength, which should be maintained for performing the activities of daily living without great difficulty.