Electromyographic (EMG) activity of selected hip and turnk luscle swas recorded diring a squat lift, and the effects of two differnt lumber spine postures were examined. Seven muscles were anlyzed: rectus abdomlnis (RA), abdominal obliques (AO), erector spinae (ES), latisslmus dorsi (LD), gluteus maximus (GM), biceps femoues (BF), and semitendionosus (ST). The muscles were chosen for their attachments to the throacolumbar fascia and their potential to act on the trunk, peivis, and hips. Seventean healthy male subjects participated in the study. Each subject did three squal lifts with a 157-N crate, with the spine in both a lordotic and kyphotic posture. The lift was dived into four equal periods. EMG activity of each muscle was quantified for ezch period and normalized to the peak amplitude of a maximal voluntary isometric contrection (MVIC) for repeated measures was used to analyze the dffects of posture on the amplitude an timing of EMG activity during the lift. Two paterns of EMG patterns of EMG activity were seen: a trunk muscle pattern (RA, AO, ES and LD)n adn a hip extensor pattern (GM, BF, ST). In thd trunk muscle pattern (TP), EMG activity was gratest in the first quarter an decressed as teh lift progressed. In the hip extensor patterns (HP), EMG activity was least in the first quarter, incresed in the second and third quarters, and decreased in the final phase of the lift. Diffeences (p<.05) were seen among subjects and in the timing of the muscle activity in all muscles. Diferences (p<.05) were found in ES EMG activity in quarters one, three, and four and for in ST EMG activity in quarter four when comparing the lifitng styles. The increassed ES EMG activity seen in the lordotic lift in the first quarteer suggests its greater involvement in lumbar spine support. This supports the clinical observation that lifting with teh luimber spine in lordosis is advantageous. No significant differnces were found in the hip extensor EMG durign the early stages of the lift.
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Vakos et al. (1994) studied this question.