RATINGS OF PERCEIVED THIGH AND BACK EXERTION IN FOREST WORKERS DURINGREPETITIVE LIFTING USING SQUAT AND STOOP TECHNIQUES

Study Design. Local thigh and low back perceived exertion (RPE), sagit tal peak load moments, and leg and trunk muscular activity during repe titive submaximal lifting, with squat and stoop technique, were invest igated. Objectives. This study analyzed changes in kinetic variables c aused by changes in body movements during the lifting bouts, and the c ontribution of the biomechanical and physiologic variables to the vari ability in the local RPE responses. Summary of Background Data. Despit e instructions that emphasize the ''correct'' lifting technique as the squat technique, the stoop technique is reported as more commonly use d in practice. Few studies have investigated the effect of lifting tec hnique on differentiated perceptual responses in repetitive lifting. M ethods. Ten experienced forest workers performed submaximal repetitive lifting bouts until steady-state VO2 was reached, using five differen t weight and frequency combinations with both squat and stoop techniqu es. Borg's scale was used for RPE measurements. Muscular activity in l umbar, hip, knee extensors, and knee flexors was recorded with surface electrodes. Kinematic data was obtained from electronic liquid-level sensors, and vertical ground reaction forces from a two-dimensional fo rce plate. Results. Low back RPE was higher for stoop than for squat, whereas the opposite was true for thigh RPE. The total accountable var iance (R2) for the biomechanical and physiologic variables to the RPE responses ranged from 0.25 (low back RPE in squat lifting) to 0.61-0.7 6 for the other assessments. During the time course in squat lifting a t the highest frequency, the knee load moment decreased and the vertic al ground reaction forces increased. Conclusions. The study indicates that ''movement strategies'' to reduce the demand on the knee-extensor muscles were used during the squat lifting bouts at the highest frequ encies, which combined with the relatively high assessed thigh exertio ns, leads to the hypothesis that quadriceps muscle exertion is the ''w eak link'' for, the squat technique. The study also indicates a discre pancy between the measured and perceived low back stress in squat repe titive lifting.