Thirty-three men (age 26–55 years) who did not exercise regularly were exercised to exhaustion using an incremental treadmill protocol. Blood lactate concentration was measured to identify lactate threshold (LT, oxygen consumption at which blood lactate concentration begins to systematically increase). The correlation coefficient for LT (ml · kg−1 · min−1) with age was not significant, but when LT was expressed as a percentage of peak oxygen consumption (VO2 peak), the correlation was r = +.69 (p < .01). This was despite a lack of significant correlation between age and VO2 peak (r = −.33). The correlation between reserve capacity (the difference between VO2 peak and LT) and age was r = −.73 (p < .01 ), and reserve capacity decreased at a rate of 3.1 ml · kg−1 · min−1 per decade. It was concluded that the percentage of VO2 peak at which LT occurs increases progressively with age, with a resultant decrease in reserve capacity.