Mechanical efficiency of rhythmic and paced work of lifting

¹ Institute of Occupational Health, Helsinki, Finland

Weights of from 2 to 10 kg were lifted to levels 5–44 cm higher and back again at the rate of 10–40 cycles/min. The optimum rate in terms of energetic efficiency was 20–30 lifts/min. With this rate, a load of 5 kg, and a lift of 12 cm, about half as much energy was expended when the subjects were permitted rapid, rhythmic completion of lifting and a compensatory pause during each min of scheduled work as when the same amount of work was performed at equal intervals throughout. The difference between rhythmic and paced work diminished to zero as the number of lifts was increased to 40/min. At loads of 2 and 10 kg and also over the distance of 5 and 44 cm, paced and rhythmic work required equal energy expenditure. The heart rate was also slower in rhythmic than in paced work. The difference was largest (16/min) when lifting 5 kg over 12 cm at the rate of 30 lifts/min. The introduction of an element of rhythm (and compensatory pause) thus resulted in a marked saving of physiological effort under strictly defined conditions.