The accuracy of using the HR/VO2 relation determined in running to predict VO2 from HR in tasks involving static and combined static/dynamic exercise was examined in a group of 8 healthy subjects (age 20-27 years). The HR measured in weight-holding tasks (with static exercise) and weight-carrying tasks (with combined static/dynamic exercise) with weights varying from 4-12 kg was inserted into the linear relation between HR and VO2 in the running task (dynamic exercise). The predicted VO2 was compared with measured value. The conclusions were as follows. It is not accurate to use a simple dynamic task to predict VO2 from a measured HR in static work. The percentage differences vary between 78 and 186%. In combined static-dynamic work a simple dynamic task can be accurately used to predict VO2 from measured HR, while carrying small weights (4, 8 and 10 kg). However, more static work (12 kg) makes the estimations poorer with a significant percentage difference in VO2 of 38%.