The effects of training on the metabolic and respiratory profile of high-intensity cycle ergometer exercise

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The tolerable work duration (t) for high-intensity cycling is well described as a hyperbolic function of power (W):W=(W'·t −1)+W a , whereW a is the upper limit for sustainable power (lying between maximumW and the threshold for sustained blood [lactate] increase,Θ lac), andW' is a constant which defines the amount of work which can be performed >W a . As training increases the tolerable duration of high-intensity cycling, we explored whether this reflected an alteration ofW a ,W' or both. Before and after a 7-week regimen of intense interval cycle-training by healthy males, we estimated (^)Θ lac and determined maximum O2 uptake \((\mu \dot V_{O_2 } )\) ;W a ;W'; and the temporal profiles of pulmonary gas exchange, blood gas, acid-base and metabolic response to constant-load cycling at and aboveW a . Although training increased \(\hat \Theta _{lac} \) (24%), \(\mu \dot V_{O_2 } \) (15%) andW a (15%),W' was unaffected. For exercise atW a , a steady state was attained for \(\dot V_{O_2 } \) , [lactate] and pH both pre- and post-training, despite blood [norepinephrine] and [epinephrine] ([NE], [E]) and rectal temperature continuing to rise. For exercise >W a , there was a progressive increase in \(\dot V_{O_2 } \) (resulting in \(\mu \dot V_{O_2 } \) at fatigue), [lactate], [NE], [E] and rectal temperature, and a progressive decrease for pH. We conclude that the increased endurance capacity for high-intensity exercise following training reflects an increasedW asymptote of theW−t relationship with no effect on its curvature; consequently, there is no appreciable change in the amount of work which can be performed aboveW a . Furthermore, regardless of training status,W a represents the upper power limit at which \(\dot V_{O_2 } \) , blood [lactate] and blood pH can eventually be stabilized. Exercise >W a , in contrast, is characterized by a steadily increasing \(\dot V_{O_2 } \) and blood [lactate], a falling blood pH and consequently, imminent fatigue.

Supported in part by a UCLA Graduate Division Doctoral Research Award