The respiratory system can be a limiting factor in maximal exercise performance. researchers from the united kingdom studied the effect of two breathing frequencies on both performance times and several physiological parameters in swimming. subjects were 10 male collegiate swimmers. here are their times in seconds to swim 200 meters at 90% of race pace when breathing every second stroke in front crawl swimming: 151.6 165.1 159.2 163.5 174.8 173.2 177.6 174.3 164.1 171.4 the correct units for the standard deviation of the data is