Respiratory function and breathing response to water- and land-based cycling at the matched oxygen uptake

The impact of underwater exercise on respiratory function remains unclear when its metabolic rate is matched with exercise performed on land. Therefore, we compared the breathing responses and respiratory function during and after water (WC)- and land (LC)-based cycling performed at the matched oxygen uptake (VO₂ ). Twelve healthy men performed 15 min of incremental WC and LC on separate days. During WC, participants cycled continuously at 30, 45, and 60 rpm (stages 1, 2, and 3) for 5 min each. During LC, participants cycled at 60 rpm for 15 min while wattage was increased every 5 min and adjusted to match VO₂ to the WC condition. Breathing patterns during cycling and spirometry data before and after cycling were collected. VO₂ during WC and LC was similar. Respiratory rate (WC: 27 ± 3 vs. LC: 23 ± 4 bpm, p = 0.012) and inspiratory flow (WC: 1233 ± 173 vs. LC: 1133 ± 200 ml/s, p = 0.035) were higher and inspiratory time (WC: 1.0 ± 0.1 vs. LC: 1.2 ± 0.2 s, p = 0.025) was shorter at stage 3 during WC than LC. After WC, forced vital capacity (p = 0.010) significantly decreased while no change was observed after LC. These results suggest that at similar metabolic rates during WC and LC, breathing is slightly shallower during WC which may have chronic effects on respiratory muscle function after multiple bouts of aquatic cycling. Underwater exercise may be beneficial for respiratory muscle rehabilitation when performed on a chronic basis.