Muscle fatty acid oxidative capacity is a determinant of whole body fat oxidation in elderly people.

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Abstract
In sedentary elderly people, a reduced muscle fatty acid oxidative capacity (MFOC) may explain a decrease in whole body fat oxidation. Eleven sedentary and seven regularly exercising subjects (65.6 ± 4.5 yr) were characterized for their aerobic fitness [maximal O2 uptake (V˙o 2 max)/kg fat free mass (FFM)] and their habitual daily physical activity level [free-living daily energy expenditure divided by sleeping metabolic rate (DEEFLC/SMR)]. MFOC was determined by incubating homogenates of vastus lateralis muscle with [1-14C]palmitate. Whole body fat oxidation was measured by indirect calorimetry over 24 h. MFOC was 40.4 ± 14.7 and 44.3 ± 16.3 nmol palmitate · g wet tissue−1 · min−1 in the sedentary and regularly exercising individuals, respectively ( P = nonsignificant). MFOC was positively correlated with DEEFLC/SMR ( r = 0.58, P < 0.05) but not with V˙o 2 max/kg FFM ( r = 0.35, P = nonsignificant). MFOC was the main determinant of fat oxidation during all time periods including physical activity. Indeed, MFOC explained 19.7 and 30.5% of the variance in fat oxidation during walking and during the alert period, respectively ( P < 0.05). Furthermore, MFOC explained 23.0% of the variance in fat oxidation over 24 h ( P < 0.05). It was concluded that, in elderly people, MFOC may be influenced more by overall daily physical activity than by regular exercising. MFOC is a major determinant of whole body fat oxidation during physical activities and, consequently, over 24 h.