Nine sedentary men (53 ± 3 yr) were studied before and after 6 d of endurance exercise training to determine the effects on maximal oxygen uptake (V˙O2 max), and on the heart rate, blood pressure, and metabolic responses to a standard bout of steady-state sub-maximal exercise. The subjects exercised approximately 1 h-d-1at about 68% of V˙O2 max. The 6-d protocol elicited no improvement in V˙O2 max, (2.50 ± 0.14 before vs 2.58 ± 0.15 1-min-1after training). Heart rates were significantly lower by 5 to 8 b-min-1, systolic blood pressures were reduced by 16 to 19 mm Hg, and blood lactate concentrations were 25 to 35% less at the same exercise intensities (60, 70, and 80% of V˙O2 max) after 6 d of exercise. Rate pressure product was about 15% lower at the same exercise intensity after 6 d of training (P<0.05). The respiratory exchange ratio during submaximal exercise was 0.02 to 0.04 units lower (P<0.05; P<0.01) after 6 d of exercise, indicating a shift in substrate utilization favoring fat oxidation. These findings suggest that short-term endurance training can induce heart rate, blood pressure, and metabolic adaptations to sub-maximal exercise before there is a significant increase in V˙O2 maxin sedentary, middle-aged men who are capable of vigorous exercise.