Postural movement pattern and muscle action sequence associated with self-paced bilateral arm flexion during standing

Investigated were postural movement pattern and action sequence of postural muscles while subjects rapidly flexed both arms during standing. The arm movement was started at the subject's own pace. Subjects were healthy individuals; 48 men and 53 women. Postural movement pattern was classified based on the movement angles of foot-leg (ankle joint) and leg-trunk (hip joint). Electromyograms were recorded from the anterior deltoid, biceps femoris, and erector spinae. The time difference between action onsets of the latter two muscles and the anterior deltoid was analyzed. Movement angles of the ankle and hip for both sexes were distributed on a similar linear regression line (y = -2.092x - 2.552 (r = -.71). The postural movement pattern was categorized based on the distribution into three types: hip flexion (in the 2nd quadrant), backward leaning (the 3rd), and hip extension (the 4th). The proportion of subjects was 26% in the hip flexion type, 55% in backward leaning type, and 19% in hip extension type. The action of biceps femoris and erector spinae significantly preceded that of anterior deltoid in the backward leaning and hip extension types but did not in the hip flexion type.