Respiratory regulation and lung volume during aquatic and land-based exercise in healthy Young adults

Elevated hydrostatic pressure during water immersion reduces lung volume and compliance at rest. These alterations may persist during exercise, influencing both the respiratory regulation and lung volume. This study compared respiratory regulation and lung volume between land-based (LC) and aquatic (AC) cycling matched for oxygen uptake (VO₂). Ten healthy young adults underwent cycling at low and moderate intensities in both environments. Expiratory gas variables (VO₂) and respiratory variables (minute ventilation and respiratory rate: V_E and RR, respectively) were continuously measured using a breath-by-breath gas analyzer system. Ventilatory equivalent for VO₂ (V_E/VO₂) was calculated. Using a spirometry system, expiratory and inspiratory reserve volumes (ERV and IRV, respectively), and tidal volume (V_T) were measured at rest and at each exercise intensity using inspiratory maneuvers and normalized to forced vital capacity (FVC). Although VO₂ was matched between conditions (p > 0.05), AC resulted in significantly higher V_E, RR, and consequently V_E/VO₂ at moderate intensity. Additionally, ERV was lower and IRV was higher during AC compared with LC across all intensities, while FVCs remained unchanged in both conditions. These findings suggest a potential mechanism by which exercise in an aquatic environment may be more effective than land-based exercise for training the respiratory system.