Electromyographic analysis of two techniques for squat lifting.

The purpose of this study was to examine the effects of two different alignments of the lumbar spine and three different loads on electromyographic activity of the erector spinae (ES) and oblique abdominal (OA) muscles during squat lifting. Nineteen healthy subjects (8 men, 11 women) participated in this study. Each subject performed squat lifts both with the lumbar spine aligned in "back-bowed-in" (BBI), or normal, lordosis and with the lumbar spine aligned in "back-bowed-out" (BBO), or relatively less, lordosis. Based on total duration, the lift was divided into two equal phases. Electromyographic activity of each muscle was quantified for each half of the lift and normalized to the total EMG produced by the muscle during a maximal voluntary isometric contraction. A three-way analysis of variance for repeated measures was used to analyze the effects of position of the lumbar spine, timing, and load on the amount of EMG activity during lifting. For all loads, ES muscle activity was greater during the first half of the BBI lift, whereas OA muscle activity was greater during the first half of the lift, regardless of the lifting style (p less than .01). The greater ES and OA muscle activity occurring during the crucial initial period in the BBI lift may provide the best protection for the lumbar spine.