The purpose of this study was to characterise the V̇O2 kinetic response to moderate intensity cycle exercise in endurance-trained (END) and sprint or power-trained (SPR) track and field master athletes ranging in age from 45 to 85 years. We hypothesised that the time constant (τ) describing the Phase II V̇O2 on-response would be smaller in the END compared to the SPR athletes, and that the τ would become greater with increasing age in both groups. Eighty-four master athletes who were competing at either the British or European Veteran Athletics Championships acted as subjects, and were classified as either END (800 m - marathon; n = 41), or SPR (100-400 m and field events; n = 43) specialists. Subjects completed two 6 minute "step" transitions to a work rate of moderate intensity on a cycle ergometer and pulmonary gas exchange was measured breath-by-breath. Analysis of variance revealed that SPR athletes had slower V̇O2 on-kinetics (i.e., greater τ) compared to END athletes at each of the age groups studied: 46-55 yrs (END: 25 ± vs. SPR: 36 ± 9s; p < 0.10), 56-65 yrs (END: 25 ± 5 vs. SPR: 35 ± 10 s; p < 0.05), 66-75 yrs (END: 29 ± 10 vs. SPR: 40 ± 13s; p < 0.05), and 76-85 yrs (END: 31 ± 10 vs. SPR: 51 ± 18 s; p < 0.05). The V̇O2 on-kinetics became slower with advancing age in the SPR athletes (p < 0.05 between 56-65 and 76-85 yrs) but were not significantly changed in the END athletes. The slower V̇O2 on-kinetics in SPR compared to END master athletes is consistent both with differences in physiology (e.g., muscle fibre type, oxidative/glycolytic capacity) and training between these specialist athletes. Master END athletes have similar τ values to their younger counterparts (∼25 s) suggesting that participation in endurance exercise training limits the slowing of V̇O2 on-kinetics with age in this population.