Relationship between maximum acceptable work time and physical workload.

For safe job design, it is necessary to know the maximum acceptable work time (MAWT) for a given workload. The aim was to establish the relationship between MAWT and physical workload. Cycling tests at six different work rates relative to personal maximum working capacity were performed by 12 young adults in the laboratory. The oxygen uptake (VO(2)) in the per cent maximum aerobic capacity (%VO(2max)), relative heart rate (RHR) and relative oxygen uptake (RVO(2)) were collected throughout the test. MAWT was determined by observing the heart rate data during the test. The results showed that MAWT was negatively correlated with %VO(2max), RHR and RVO(2) (p < 0.01). Three exponential regression models were obtained and all their R(2) > 0.80. These models suggest that long-hour shifts (> 10 h) should assign a lower work intensity than for an 8-h workday. It is also logical that the workload limit for a 4-h work shift could be set at about 10% VO(2max) higher than the suggested limit for an 8-h workday.