A physiological study of the repetitive lifting capabilities of healthy young males

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Abstract
In emergencies, it may be necessary for men to manually handle large quantities of materials. Although data are available for loads carried on the back and there are specific civilian and military recommendations concerning safe maximum loads and acceptable workloads for repetitive lifting, data quantifying maximum capabilities for repetitive lifting tasks are not available. A preliminary study was undertaken to determine the relationship between lifting rate and time to exhaustion using 3 standard loads. Eight healthy fit, well trained young soldiers bi-manually lifted 3 loads (25, 50 and 75% of their maximal lifting capacity (MLC) for a single lift to waist height) from the floor to a platform at waist height (40% stature) situated directly in front of them at lifting rates of 2, 3 and 4 lifts/min (75% MLC), 4, 6 and 8 lifts/min (50% MLC) and at 8, 10 and 12 lifts/min (25% MLC) for 1 h or until they became exhausted or were unwilling or unable to continue or maintain the prescribed lifting rate. The observed lifting duration (LD obs) was noted, or if the subject was not exhausted after 1 h of lifting, he estimated his lifting duration (LD est). O2 consumption ($D+VO2) and heart rate (HR) were measured for 1 min each 10 min. The mean (SD) LD obs and LD est at 25% MLC were 156(57), 99(61) and 65(34) min for 8, 10 and 12 lifts/min, respectively. At 50% MLC they were 111(65), 72(45) and 35(18) min for 4, 6 and 8 lifts/min, respectively. At 75% MLC they were 93(69), 61(35) and 30(23) min for 2, 3 and 4 lifts/min, respectively. The mean relationships between load and lifting rate at 50, 35 and 23% .ovrhdot.VO2 max (determined for uphill treadmill running), and for a HR of 110 beats/min were constructed. These results provided a preliminary quantification of maximum human capabilities in repetitive lifting and an indication of the upper limits of tolerance for industrial workers undertaking repetitive lifting over an 8 h work day. Further work is necessary to evaluate inter-personal and ergonomic factors in repetitive lifting tasks.