PÉRONNET, F., G. THIBAULT, E. C. RHODES, and D. C. MCKENZIE. Correlation between ventilatory threshold and endurance capability in marathon runners.Med. Sci. Sports Exerc., Vol. 19, No. 6, pp. 610–615, 1987. The purpose of the study was to develop an index of endurance capability [i.e., “the ability to sustain a high fractional utilization of maximal oxygen uptake (VO2max) for a prolonged period of time”]. The index was based on the linear reduction of fractional utilization of VO2maxwith total running time greater than 7 min plotted on a log scale. The endurance index estimated from VO2maxrunning efficiency and the marathon performance of 18 male runners (30 ± 7 yr old; VO2max= 66 ± 5 ml.kg-1.min-1) ranged between −4.07 and −9.96% VO2ma*.ln t-1(mean ± SD = −6.40 ± 1.50) and was not related to VO2max(r = 0.107) or speed in the marathon race (r = 0.354). However, the endurance index was closely related (r = 0.853) to the fractional utilization of VO2maxat ventilatory threshold (breakaway of the excess CO2elimination curve) which occurred at 76.1 ± 5.5% VO2maxin response to a graded treadmill test. These results indicate that: (i) running time on long distance races is not, per se, an adequate measure of endurance capability because of the major contribution of VO2maxto long distance running performance; (ii) the endurance index expressed as %VO2max.1n t-1is an objective and independent index of endurance capability; and (iii) runners with a high endurance capability tend to hyperventilate at higher relative workload during a graded treadmill test.