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

Introduction: 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.

Methods: 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.

Results: 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.

Conclusions: 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.