The Mechanics of Breathing during Swimming

The thorax undergoes unique conditions while swimming. Hydrostatic pressure from water immersion places an external load on the thorax and increases airway resistance, and the horizontal body position results in central venous engorgement and an associated reduction in lung compliance. The aforementioned factors likely increase the work of breathing (Wb); however, this hypothesis remains untested.

This study aimed to compare Wb during freestyle swimming relative to cycling and to characterize the differences in the cardiorespiratory responses to swimming relative to cycling in the same individuals.

Eight collegiate swimmers (four men and four women, age = 22 ± 2 yr) performed an incremental swim test while tethered to a resistance apparatus. On a separate day, subjects performed an incremental cycle test. During swimming and cycling, metabolic and ventilatory parameters were measured using a customized metabolic cart, and inspired Wb was quantified using an esophageal balloon catheter.

Swimming and cycling elicited statistically similar levels of peak oxygen uptake (3.87 ± 0.92 vs 4.20 ± 0.83 L·min, P = 0.143). However, peak minute ventilation (V˙E) (118 ± 3 vs 154 ± 25 L·min) and heart rate (164 ± 19 vs 183 ± 8 bpm) were significantly lower during swimming relative to cycling (both P < 0.05). Inspired Wb was higher at a V˙E of 50 L·min (+27 ± 16 J·min), 75 L·min (+56 ± 23 J·min), and 100 L·min (+53 ± 22 J·min) during swimming compared with cycling (all P < 0.05). Periods of interbreath apnea were observed while swimming (duration = 0.13-2.07 s).

We interpret our findings to mean that the horizontal body position and hydrostatic pressure on the chest wall requires swimmers to generate greater inspiratory pressures to sustain adequate V˙E during exercise.