THE EFFECTS OF TRAINING ON THE METABOLIC AND RESPIRATORY PROFILE OF HIGH-INTENSITY CYCLE ERGOMETER EXERCISE

The tolerable work duration (t) for high-intensity cycling is well described as a hyperbolic function of power (W):W=(W'·t-1)+Wa, where Wa is the upper limit for sustainable power (lying between maximum W and the threshold for sustained blood [lactate] increase, Θlac), and W' is a constant which defines the amount of work which can be performed >Wa. As training increases the tolerable duration of high-intensity cycling, we explored whether this reflected an alteration of Wa, W' or both. Before and after a 7-week regimen of intense interval cycle-training by healthy males, we estimated (^)Θlac and determined maximum O2 uptake {Mathematical expression};Wa;W'; and the temporal profiles of pulmonary gas exchange, blood gas, acid-base and metabolic response to constant-load cycling at and above Wa. Although training increased {Mathematical expression} (24%), {Mathematical expression} (15%) and Wa (15%), W' was unaffected. For exercise at Wa, a steady state was attained for {Mathematical expression}, [lactate] and pH both pre- and post-training, despite blood [norepinephrine] and [epinephrine] ([NE], [E]) and rectal temperature continuing to rise. For exercise >Wa, there was a progressive increase in {Mathematical expression} (resulting in {Mathematical expression} 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 increased W asymptote of the W-t relationship with no effect on its curvature; consequently, there is no appreciable change in the amount of work which can be performed above Wa. Furthermore, regardless of training status, Wa represents the upper power limit at which {Mathematical expression}, blood [lactate] and blood pH can eventually be stabilized. Exercise >Wa, in contrast, is characterized by a steadily increasing {Mathematical expression} and blood [lactate], a falling blood pH and consequently, imminent fatigue. © 1990 Springer-Verlag.