PHYSIOLOGICAL AND SUBJECTIVE RESPONSES TO MAXIMAL REPETITIVE LIFTING EMPLOYING STOOP AND SQUAT TECHNIQUE

To establish safe levels for physical strain in occupational repetitiv e lifting, it is of interest to know the specific maximal working capa city. Power output, 02 consumption, heart rate and ventilation were me asured in ten experienced forestry workers during maximal squat and st oop repetitive lifting. The two modes of repetitive lifting were also compared with maximal treadmill running. In addition, electromyogram ( EMG) activity in four muscles was recorded and perceived central, loca l low-back and thigh exertion were assessed during the lifting modes. No significant difference was found in power output between the two li fting techniques. Despite this the mean O2 consumption was significant ly greater during maximal squat lifting [38.7 (SD 5.8) ml . kg-1 . min -1] than maximal stoop lifting [32.9 (SD 5.7) ml . kg-1 . min-1] (P<0. 001). No significant correlation was found between O2 consumption (in millilitres per kilogram per minute) during maximal treadmill running and maximal stoop lifting, while O2 consumption during maximal squat l ifting correlated highly with that of maximal treadmill running (r=0.9 28, P<0.001) and maximal stoop lifting (r=0.808, P<0.01). While maxima l heart rates were significantly different among the three types of ex ercise, no such differences were found in the central rated perceived exertions. Perceived low-back exertion was rated significantly lower d uring squat lifting than during stoop lifting. The EMG recordings show ed a higher activity for the vastus lateralis muscle and lower activit y for the biceps femoris muscle during squat lifting than during stoop lifting. Related to the maximal voluntary contraction, the erector sp inae muscle showed the highest activity irrespective of lifting techni que.