HAGBERG, JAMES A. and EDWARD F. COYLE. Physiological determinants of endurance performance as studied in competitive racewalkers.Med. Sci. Sports Exerc., Vol. 15, No. 4, pp. 287–289, 1983. The physiological factors that relate to 20-km performance were studied in eight competitive racewalkers. The racewalking velocity at the blood lactate threshold (LT) during steady-state exercise was highly correlated to racewalking pace (r=0.94) and predicted performance times to within 0.6%, which agrees with previous observations on runners. The two factors that contribute to velocity at LT are O2uptake at LT (&OV0312;o2at LT) and submaximal racewalking economy (measured as the &OV0312;o2at a standard velocity). Oxygen uptake at LT was significantly correlated (r=0.89) to performance in the racewalkers in the present investigation, which agrees with previous observations of runners. Submaximal economy was significantly correlated to performance in the racewalkers (r=0.82). Maximal oxygen uptake measured during racewalking was not significantly correlated (r=0.62) to performance. These data indicate that the velocity at LT correlates closely to performance in racewalkers and that the factor of submaximal economy, which partly determines velocity at LT, is related more to performance ability in racewalking than was previously observed in running.