Age-related decline in RMR in physically active men: relation to exercise volume and energy intake

We tested the hypothesis that resting metabolic rate (RMR) declines with ag e in physically active men (endurance exercise greater than or equal to3 ti mes/wk) and that this decline is related to weekly exercise volume (h/wk) a nd/or daily energy intake. Accordingly, we studied 137 healthy adult men wh o had been weight stable for greater than or equal to 6 mo: 32 young [26 +/ - I (SE) yr] and 34 older (62 +/- 1 yr) sedentary males (internal controls) ; and 39 young (27 +/- 1 yr) and 32 older (63 +/- 2 yr) physically active m ales (regular endurance exercise). RMR was measured by indirect calorimetry (ventilated hood system) after an overnight fast and similar to 24 h after exercise. Because RMR is related to fat-free mass (FFM; r = 0.76, P < 0.00 1, current study), FFM was covaried to adjust RMR (RMRadj). RMRadj was lowe r with age in both the sedentary (72.0 +/- 2.0 vs. 64.0 +/- 1.3 kcal/h, P < 0.01) and the physically active (76.6 +/- 1.1 vs. 67.9 +/- 1.2 kcal/h, P < 0.01) males. In the physically active men, RMRadj was related to both exer cise volume (no. of h/wk, regardless of intensity; r = 0.56, P < 0.001) and estimated energy intake (r = 0.58, P < 0.001). Consistent with these relat ions, RMRadj was not significantly different in subgroups of young and olde r physically active men matched either for exercise volume (h/wk; n = 11 ea ch) or estimated energy intake (kcal/day; n = 6 each). These results indica te that 1) RMR, per unit FFM, declines with age in highly physically active men; and 2) this decline is related to age-associated reductions in exerci se volume and energy intake and does not occur in men who maintain exercise volume and/or energy intake at a level similar to that of young physically active men.