KOHRT, W. M., J. S. O'CONNOR, and J. S. SKINNER. Longitudinal assessment of responses by triathletes to swimming, cycling, and running. Med. Sci. Sports Exerc., Vol. 21, No. 5, pp. 569–575, 1989. Fourteen triathletes (eight male, six female) were tested four times (in February, May, August, and October) to monitor adaptations to training for a triathlon (1.9-km swim, 90.3-km bike, 21.1-km run). V̇O2max was measured during treadmill running (TR), cycle ergometry (CE), and tethered swimming (TS). Lactate threshold (LT), defined as the V̇O2 at a lactate concentration of 4 mM, was determined during TR and CE. In all sessions, TS V̇O2max was less than TR and CE (P < 0.05), and CE was less than TR (P < 0.05). Means for Session I were 57.4, 53.4, and 48.3 ml·min-1·kg-1 for TR, CE, and TS, respectively. Corresponding values for Session IV were 58.4, 56.0, and 47.8 ml·min-1·kg-1. The only significant increase in V̇O2max, was for CE (5%). V̇O2 at the LT increased from Session I to IV for both TR (6%) and CE (10%); the LT for TR was at a higher V̇O2 than for CE in all sessions. The percent V̇O2max at LT for TR in Sessions I and IV was 80 and 85%, respectively. Analogous values for CE were 72 and 76%. The minimal increases in V̇O2max suggest that subjects had reached their potential in this parameter. Improvements in race performance were probably attained through peripheral adaptations, as suggested by increases in the V̇O2 at LT. The occurrence of the LT at a lower percent V̇O2max in cycling than in running suggests that the triathletes had greater potential for improvement in cycling.