[Influence of physical workload patterns and breaks on heart rate recovery]

It is necessary to try to achieve quick recovery from work strain by setting adequate breaks and shortening continuous working hours to prevent the accumulation of fatigue. However, there has been no research investigating the influence of the timing and lengths of breaks on individual aerobic capacities in recovery from work strain. In this study, we set three load patterns based on the length and timing of breaks: "no breaks", "one break" and "regular small breaks". We examined the differences of the heart rate variation in the recovery time after working considering the individual aerobic capacities (VO(2)max) of ten male subjects (mean age 22.3 +/- 1.7 yr) in the case of 50 W or 100 W workloads on a bicycle ergometer. When individual aerobic capacity was not considered, the "regular small breaks" condition led to the quickest recovery to the level of the resting heart rate at 50 W workload. Not all conditions showed heart rate recovery within 30 min at 100 W workload. On the other hand, when individual aerobic capacity was considered, the "regular small breaks" condition showed the quickest recovery to the level of the resting heart rate at 50 W workload in the low aerobic capacity group (VO(2)max mean 42.2 +/- 3.7 ml/kg/min). However, in the high aerobic capacity group (VO(2)max mean 54.5 +/- 4.1 ml/kg/min), the "regular small breaks" condition resulted in the quickest recovery of the level to the resting heart rate at 100W workload. Two-way repeated measures ANOVA was performed for the recovery time with respect to the rate of increase from resting heart rate to examine the influence on heart rate recovery of physical activity loads, workload patterns and individual fitness. Physical activity loads were strongly related to the increase from resting heart rate in recovery time, and workload patterns showed that the regular small breaks condition was related to the heart rate recovery in the high fitness subjects in the case of the exercise intensity of 100 W. The effect of work strain decreased by workload patterns was defined by the relationship between physical activity load and individual fitness. In future occupational health activities, it will be important to manage work in order to aim for quick recovery from work strain by using ergonomics. The evaluation of the level of the physical activity load and distribution of proper break times during working in addition to individual aerobic capacities are important in considerations of quick recovery from work strain.