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

Summary

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.