Physiological and Psychophysical Comparison between a One and Two-Handed Identical Lifting Task

The 1991 NIOSH (National Institute for Occupational Safety and Health) revised lifting equation’s objective is to prevent or reduce lifting-related injuries, especially of the low back. However, the lifting equation is only applicable to two-handed lifting tasks. Oneand twohanded repetitive lifting tasks are a consistent part of many occupations. Understanding the metabolic demands of oneand two-handed lifting tasks is important in job design strategies related to productivity and injury prevention. This study compared the metabolic response of an identical lifting task performed with either one or two hands. Thirty-three healthy volunteers participated (21 males, 12 females; 26+5 yr; 177.5+6.9 cm; 72.5+9.8 kg; grip strength, right = 43.8+11.4 kg, left = 42.6+12.4 kg; all right hand dominant). Subjects transferred a 12.5 kg milk crate individually back and forth from the floor to a table. Standard milk crate handles established identical coupling for each hand. Distance crate traveled from floor to table was 152.4 cm horizontally and 74.9 cm vertically. Subjects performed three, 5 minute work bouts in random order with either the dominant hand, nondominant hand, or both. Three minutes of rest was allowed between each bout. Pace was constant at 8 lifts per minute. Lifting technique was self-selected by the subject. Metabolic parameters were monitored throughout the work bouts. Steady state data from minute 2 to minute 5 was used for analysis with ANOVA. Results were as follows: (mean (sd); d=dominant, nd=non-dominant, b=both hands) ml/kg/min: d = 14.3 (2.8), nd = 14.4 (3.0), b = 15.7 (3.2); l/min: d = 1.0 (0.2), nd = 1.0 (0.2), b = 1.1 (0.2); kcal/min: d = 5.1 (1.0), nd = 5.1 (1.0), b = 5.6 (1.1); RER: d = 0.9 (0.1), nd = 0.9 (0.1), b = 0.9 (0.1); HR: d = 103.4 (12.2), nd = 105.4 (11.5), b = 107.1 (12.0); RPE: d = 9.4 (1.9), nd = 10.0 (1.9), b = 9.4 (1.9). No significant difference (p<0.05) occurred on any parameter between the three conditions. In conclusion, there were no differences in metabolic cost or perceived exertion when performing a paced, oneor two-handed identical lifting task with self-selected lifting technique. KeywordsRevised NIOSH lifting equation, grip, work.