Determinants of endurance in well-trained cyclists
EDWARD F. COYLE, ANDREW R. COGGAN,
MAR1 K. HOPPER, AND THOMAS J. WALTERS
J. Appl. Physiol. 64(6): 2622-2630,1988.-
Fourteen competitive cyclists who possessed a similar maximum 02 consumption (VO 2 max; range, 4.6-5.0 l/min) were compared regarding blood lactate responses, glycogen usage, and endurance during submaximal exercise.
Seven subjects reached their blood lactate threshold (LT) during exercise of a relatively low intensity (group L) (i.e., 65.8 t 1.7% 7jozrnax), whereas exercise of a relatively high intensity was required to elicit LT in the other seven men (group H) (i.e., 81.5 k 1.8% TOM,,; P < 0.001).
Time to fatigue during exercise at 88% of VOLT, was more than twofold longer in group H compared with group L (60.8 k 3.1 vs. 29.1 k 5.0 min; P < 0.001). Over 92% of the variance in performance was related to the %VO~ mm at LT and muscle capillary density.
The vastus lateralis muscle of group L was stressed more than that of group H during submaximal cycling (i.e., 79% V0 2 mm), as reflected by more than a twofold greater (P c 0.001) rate of glycogen utilization and blood lactate
concentration.
The quality of the vastus lateralis in groups H and L was similar regarding mitochondrial enyzme activity, whereas group H possessed a greater percentage of type I muscle
fibers (66.7 & 5.2 vs. 46.9 t 3.8; P < 0.01).
The differing metabolic responses to submaximal exercise observed between the two groups appeared to be specific to the leg extension phase of cycling, since the blood lactate responses of the two groups were comparable during uphill running.
These data indicate that endurance can vary greatly among individuals with an equal VO2max,
The factors associated with a high %VO~ mm at LT were years of cycling experience (r = 0.75; P c 0.01) and percent type I muscle fibers (r = 0.55; P c 0.05).
It appears that intense cycle training performed for ~5 yr compared with 2-3 yr promotes continued adaptations that reduce muscle glycogenolysis specifically when cycling.