The difference in cardiopulmonary response between supine exercise and sitting exercise was assessed by the following protocols.
1) Cardiopulmonary exercise testing utilizing the ramp protocol with a bicycle ergometer (20 W/min) was performed by nine healthy Japanese men (mean age, 19.9 yr) in a sitting and a supine position. Oxygen uptake, heart rate and blood pressure were measured during the test. Blood was sampled in order to measure noradrenaline (NA) and angiotensin II (ANG II) in the resting control state and immediately after exercise.
2) Single-level exercise testing at 100 W was performed on another day. The cardiac index (CI) was computed from the cardiac output, which was measured using the dye-dilution method in the resting control state and during exercise.
The results were as follows:
1) Heart rate and blood pressure during exercise had a tendency to be lower in the supine position compared to the sitting position, although not significantly.
2) Anaerobic threshold (AT) was lower in the supine position than in the sitting position exercise, (18.3±2.6 ml/kg/min and 21.7±1.9 ml/kg/min, respectively) .
3) NA and ANG II in the supine position were slightly lower than in the sitting position.
4) At rest, the CI in the sitting position was significantly less than in the supine position; however, the CI during the 100 W exercises was the same in both the supine and sitting positions.
It is concluded that blood flow to active muscle during 100W exercise is lower in the supine than in the sitting position. This is thought to be due to changes in blood redistribution and lowered blood flow to active muscle in the supine position, creating a lower AT.