Cardiopulmonary Response during Supine and Sitting Bicycle Exercises

The effect of body position on cardiopulmonary response was assessed by the following protocols: 1) Cardiopulmonary exercise testing with a bicycle ergometer (20 W/min) was performed on nine healthy men (mean age; 19.9 years) in a sitting and a supine position. Oxygen uptake, heart rate and blood pressure were measured during the test. Noradrenaline and Angiotensin II were analyzed at rest and after exercise. 2) Single-level exercise testing at 100 W was performed. The cardiac index was computed from the cardiac output, which was measured using the dye-dilution technique at rest and during exercise. The results were as follows: 1) Anaerobic threshold was lower in the supine than in the sitting. 2) Noradrenaline and Angiotensin II were slightly lower in the supine than in the sitting. 3) The cardiac index at rest was slightly greater in the supine, and that during 100 W exercise was the same in both positions. It is concluded that the blood flow to active muscle during 100 W exercise is lower in the supine than in the sitting. The etiology of lower anaerobic threshold in the supine is thought to be due to lowered blood flow to active muscle.