The effect of prior exercise on efficiency and VO₂ kinetics is well established at pedal rates between 60-95 revs.min^-1 (Burnley et al, 2002; Sahlin et al, 2005). When considering such responses the contraction frequency at which exercise is performed is crucial as this may alter the position of the working muscle on the efficiency-velocity relationship. Indeed, passive increases in muscle temperature (T_m) have different effects on efficiency depending on contraction frequency (Ferguson et al, 2002). The effect of prior exercise has not been studied at distinct pedal rates. The aim of this study was to investigate the effect of prior exercise on mechanical efficiency and VO₂ kinetics at 60 and 120 revs.min^-1. With ethics committee approval, 6 male subjects (age 25 ± 5 yrs, height 1.82 ± 0.09 m, body mass 79 ± 16 kg) performed 6 min cycling exercise (power output halfway between LT and VO_2peak) at 60 and 120 revs.min^-1, under control conditions (C60 and C120) and after prior exercise (P60 and P120). Prior exercise consisted of two 2 min cycling bouts, separated by 2 min rest, with a third bout to exhaustion, performed at 100% VO_2peak at 90 revs.min^-1. T_m was measured prior to the 6 min exercise. VO_2peak (breath-by-breath) was measured throughout and modelled using non-linear regression. Net mechanical efficiency was calculated from the VO_2peak, RER and measurement of post exercise blood lactate concentration. Statistical analyses were performed using repeated measures ANOVA and Bonferroni corrected paired t-tests where appropriate. Data is presented as means ± SD. Prior exercise increased (P<0.05) T_m by 3.4 ± 0.8 °C. The absolute primary amplitude of VO₂ was higher (P<0.05) after prior exercise at both pedal rates, and to a greater extent at 120 revs.min^-1 (Table 1). The decrease in the VO₂ slow component as a result of prior exercise was greater (P<0.05) at 120 compared to 60 revs.min^-1 (Table 1). Consequently, prior exercise reduced mechanical efficiency at 60 and 120 revs.min^-1 (by 2.4 ± 2.3 and 2.3 ± 1.4 %, respectively). The present data demonstrate that compared to when Tm is passively increased the effect of prior exercise on efficiency is not necessarily dependent on contraction frequency.