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

Abstract

In emergencies, it may be necessary for men to manually handle very 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. We have therefore undertaken a preliminary study to determine the relationship between lifting rate and time to exhaustion using three standard loads. Eight healthy fit, well-trained young soldiers bi-manually lifted 3 loads lpar;25, 50 and 75percnt; 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⁻¹ (75% MLC), 4,6 and 8 lifts min⁻¹ (50% MLC) and at 8,10 and 12 lifts min⁻¹ (25% MLC) for one hour 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 one hour of lifting, he estimated his lifting duration (LD est). Oxygen consumption ([Vdot]O₂) and heart rate (HR) were measured for 1min each 10min. The mean (S.D.) LD obs and LD est at 25% MLC were 156(57), 99(61) and 65(34) minutes for 8, 10 and 12 lifts min⁻¹ respectively. At 50% MLC they were 111(65), 72(45) and 35(18) minutes for 4, 6 and 8 lifts/min respectively. At 75% MLC they were 93(69), 61(35) and 30(23) minutes for 2, 3 and 4 lifts min⁻¹ respectively. The mean relationships between load and lifting rate at 50%, 35% and 23% [Vdot]O₂ max (determined for uphill treadmill running), and for a HR of 110 beats min⁻¹ were constructed. These results provide 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-hour work day. Further work is necessary to evaluate inter-personal and ergonomic factors in repetitive lifting tasks.

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Notes on contributors

C. M. PATEMAN

Present address: Materials Handling Research Unit, Institute of Industrial and Environmental Health and Safety, Surrey University, Guildford, Surrey, England