Effects of submersion on VO₂: comparing maximum aerobic exertion on land and underwater

Submersion results in blood redistribution into the pulmonary circulation, causing changes in pulmonary compliance and increased cardiac preload. Few studies have compared incremental exercise to exhaustion (VO₂ max testing) in a dry environment with exercise underwater. We hypothesized that the physiological effects of submersion would result in lower heart rate (HR), minute ventilation (V_E), and peak oxygen uptake (VO₂ peak) compared with dry conditions.

Fourteen male and four female volunteers completed two VO₂ peak testing sessions with approximately two hours between trials: first in the dry laboratory on a cycle ergometer and second while fully submersed in a prone position with zero static lung load. HR was monitored via ECG, and inspiratory and expiratory gas compositions were recorded using a metabolic cart. The tests were terminated once the subject reached exhaustion.

Absolute VO₂ peak was lower in the submersed VO₂ max trial (37.1 ± 7.0 mL•kg^-1•min^-1) compared with dry exercise (45.8 ± 8.9 mL•kg^-1•min^-1) p < 0.001. HR and V_E were also lower in the submersed trial.

VO₂ peak while submersed is reduced relative to dry VO₂ peak, which may be partly due to a decrease in heart rate and a reduction in V_E.