Effect of combined dynamic and static workload on heart rate recovery cost.

The objective of the present study was to develop a simplified heart rate recovery cost (RC) model and to validate it under various degrees of dynamic and static task components. The simplified model of heart rate recovery cost consisted of two parameters: heart rate increase (delta HR) and recovery time (T). The following formula revealed their relationship: RC (recovery cost) = T x (delta HR-1)/ln delta HR Exercise, including cycling at three work loads (40, 60, 80 W) on a cycle ergometer, and carrying a backpack with three weights (0, 7.5, 15 kg) was studied in seven male subjects. For each exercise condition, resting HR, working HR, and recovery time (T) were recorded. The results support the hypothesis that neither heart rate increase nor recovery cost could completely assess the physical stress incurred when performing a combined dynamic/static exercise. The delta HR measurement was more sensitive to the increase of static load and the calculated RC value increased with both dynamic and static load. The simplified model of recovery cost can be easily applied without interfering with a person's work routine and without discomfort.