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This study examined the effect of heavy-intensity warm-up exercise on O₂ uptake (V˙o ₂) kinetics at the onset of moderate-intensity (80% ventilation threshold), constant-work rate exercise in eight older (65 ± 2 yr) and seven younger adults (26 ± 1 yr). Step increases in work rate from loadless cycling to moderate exercise (Mod₁), heavy exercise, and moderate exercise (Mod₂) were performed. Each exercise bout was 6 min in duration and separated by 6 min of loadless cycling.V˙o ₂ kinetics were modeled from the onset of exercise by use of a two-component exponential model. Heart rate (HR) kinetics were modeled from the onset of exercise using a single exponential model. During Mod₁, the time constant (τ) for the predominant rise in V˙o ₂(τV˙o ₂) was slower (P < 0.05) in the older adults (50 ± 10 s) than in young adults (19 ± 5 s). The older adults demonstrated a speeding (P < 0.05) of V˙o ₂kinetics when …