Lower Limb Muscular Activation During Transitions to Symmetric High Knee Flexion Postures in Young Females

OCCUPATIONAL APPLICATIONS Movements involving substantial knee flexion, such as squatting and kneeling, are common in many occupations and in some activities of daily living. However, the level of muscle activity required to perform these movements has not been well investigated, and only peak activations have been previously reported from a few leg muscles. This limits our understanding of the physical demands on workers when attempting to understand joint degenerative disease risk or developing guidelines for occupations commonly using these postures. The present study compared kneeling and squatting movements, based on activity levels, from seven leg muscles. Minimal differences were found when descending into these movements, but higher activity from two thigh muscles were observed when ascending from squatting when compared to kneeling. Therefore, future modeling efforts may use these data to verify estimates of muscle activity for joint loading prediction of symmetric descending transitions to high knee flexion postures.

TECHNICAL ABSTRACT Rationale: Many occupations and activities of daily living require individuals to use their full range of knee motion, but fundamental data on muscle activity is lacking. Lower limb data are limited above 100° of knee flexion and have not been reported for dynamic movements with high knee flexion. Purpose: To determine if the levels of quadriceps, hamstring, gastrocnemii, and tibialis anterior activity differed between two symmetric high flexion movements (heels-up squat and dorsi-flexed kneel). Methods: Electromyographic signals from the dominant lower limb were normalized to maximum voluntary contractions and discretized in 1° increments of knee flexion angle; principal component analysis was then used as a means of comparing time-series data between dynamic movements. The descent and ascent phases of these movements were assessed separately. Results: Semitendinosus and vastus lateralis at peak principal component scores were 14.2% and 16.1% maximum voluntary contractions higher in the ascending phase, respectively, during squatting when compared to kneeling. Negligible differences were present in the biceps femoris during the descending phase. Conclusions: Our findings suggest that, for ascent to standing, activation waveforms for the semitendinosus and vastus lateralis muscles are different, at respective knee flexion angles, during these movements. However, muscular activity is similar between movements during descent.