A comparative study of load sharing among back and leg muscles during squat and half-kneeling lifts

This paper presents the results of a comparative study of load sharing among back and leg muscles during squat and half-kneeling lifts. 19 young and healthy subjects with no history of low back pain or other musculoskeletal disorders participated in the study. Muscle activity was measured using electromyography (EMG) technique. Surface EMG electrodes were placed bilaterally at the erector spinae, quadriceps and hamstring muscles. Muscle activities were determined at different force levels representing 40, 60 and 80 percent of maximal voluntary contraction (MVC). The results showed increase in normalised mean RMS (root mean squared) values of EMG of for all the muscles with increasing force levels in both squat and half kneeling lifts. Contralateral and ipsilateral ratio parameters were used to determine the degree of load sharing among the muscles in both lifting postures. Statistical analysis of the mean RMS values and the contralateral and ipsilateral ratio parameters revealed no significant differences between squat and half kneeling lifts. The paper discusses the implications of the results for preventing injuries during manual handling and provides suggestions for future research.