Dekerle, J., Brickley, G., Alberty, M., & Pelayo, P. (2009). Characterizing the slope of the distance-time relationship in swimming. Journal of Science and Medicine in Sport, July 2 [E-publication].

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This study assessed whether the critical speed calculated by the slope of the distance-time relationship represents the boundary between the heavy and severe intensity domains in swimming and would be sustainable during intermittent exercise. Male competitive swimmers (N = 9) performed, a) four fixed distance (100-200-400-800m) all-out efforts to determine the critical speed and peak oxygen uptake (VO2); b) three constant-speed efforts to exhaustion at and 5% above and 5% below the critical speed; and c) a set of 10 x 400 m at the critical speed with a 40-second recovery between repetitions.

Capillary blood lactate concentration, peak oxygen uptake, and ratings of perceived exertion remained stable at -5% of critical speed. Time to exhaustion decreased at 5% above critical speed. Peak oxygen uptake was reached at exhaustion. Critical speed could only be maintained for an average of ~24 minutes with ratings of perceived exertion and lactate concentration increasing and peak oxygen uptake reaching its peak. Ratings of perceived exertion increased but blood lactate remained stable throughout the ten 400-m blocks performed at critical speed (overall average time for the set was ~54 minutes).

Implication. The physiological responses when swimming 5% below and 5% above critical speed characterize the heavy and severe intensity domains, respectively. While critical speed lies within the severe intensity domain, intermittent swims at that intensity induce lactate steady state alongside high rates of perceived exertion.

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