The respiratory system is not typically associated with the limiting factor in maximal exercise, and the influence of inspiratory (breathing inward) muscle fatigue during maximal exercise is unclear. Studies suggest a long and short duration high-intensity exercise causes inspiratory muscle fatigue leading to impaired performance. Breathing during swimming is especially important since breathing frequency is limited. The constraints of swimming make breathing harder and place higher stress on the inspiratory muscles compared to land sports. The study in review looked at the influence of different breathing frequency (breathing every two strokes vs. every four strokes) on inspiratory muscle fatigue during a high intensity (90% of the best time) 200-m front crawl. Inspiratory muscle fatigue was measured by maximal inspiratory pressure, which is measured by breathing as much air in as fast as you can. The study also looked at the swimmer’s heart rate, blood lactate, and time levels following the swim.
Ten male collegiate swimmers each swimmer swam the 200-m breathing every two and four strokes with a day in between trials. The results indicated the inspiratory muscles were more fatigued breathing every four strokes opposed to breathing every two strokes (10% difference in maximum inspiratory pressure). Blood lactate was 15% lower after breathing every four strokes than breathing every two. Heart rates were not significantly different between trials, either were their times (however, breathing every two was .4 faster).
These results are counterintuitive. If you breathe less, shouldn’t the inspiratory muscles be less fatigued? It is believed holding one’s breath leads to alveolar hypoventilation (alveolar are the air sacs in the lungs) causing carbon dioxide retention stressing the inspiratory muscles. Taking fewer breaths increases the amount of air one takes in and expands the chest wall, hyper-expanding the wall and putting them in a disadvantageous position.
A higher lactate is believed to stem from the same physiological adaptation. The increased carbon dioxide impairs the lactate disposal from the muscle to the blood. 
This impairment is relieved once normal breathing occurs and the researchers should have taken lactate values long after the performance to see a rise in blood lactate. Also, even though the times were not significantly different, the 0.4-time difference could account for some lactate variation.
The main point from this study is that inspiratory muscle fatigue does occur during swimming. This fatigue is greater with less frequent breathing.
References:
- Jakovljevic D, McConnell A. Influence of different breathing frequencies on the severity of inspiratory muscle fatigue induced by high-intensity front crawl swimming. J Strength Cond Res. Jul 2009;23(4):1169-1174.
Comments 1
Couple of things, generally the stroke is more efficient with less breathing, to less lactate?
Also the speed of the swimmers is important, % of personal best.
The volume of air inhaled each breath is also important, swimmers could be breathing deeper with less frequency.
Interesting findings.