Muscle protein synthesis response to exercise training in obese, older men and women

Abstract

Introduction: Physical activity and eating are two major physiological muscle growth stimuli. Although muscle protein turnover rates are not different in young and middle-aged men and women, we recently found that the basal rate of muscle protein synthesis is greater and the anabolic response to mixed-meal intake is blunted in 65- to 80-yr-old women compared with men of the same age. Whether older women are also resistant to the anabolic effect of exercise is not known.

Methods: We measured the rate of muscle protein synthesis (both during basal, postabsorptive conditions and during mixed-meal intake) before and after 3 months of exercise training in obese, 65- to 80-yr-old men and women.

Results: At the beginning of the study (before training) the basal, postabsorptive muscle protein fractional synthesis rate (FSR) was significantly greater in women than in men (0.064 ± 0.006%·h(-1) vs 0.039 ± 0.006%·h(-1), respectively, P < 0.01), whereas the meal-induced increase in the muscle protein FSR was greater in men than in women (P < 0.05). In men, exercise training approximately doubled the basal muscle protein FSR (P = 0.001) but had no effect on the meal-induced increase in muscle protein FSR (P = 0.78). In women, exercise training increased the muscle protein FSR by ~40% (P = 0.03) and also had no effect on the meal-induced increase in muscle protein FSR (P = 0.51).

Conclusions: These results suggest that there is significant sexual dimorphism not only in the basal, postabsorptive rate of muscle protein synthesis but also in the anabolic response to feeding and exercise training in obese, older adults.

Figure 1

Skeletal muscle protein fractional synthesis rate during basal, post-absorptive conditions and during mixed meal feeding in 65–80 y old men (top) and women (bottom) before and after completing a 3-months long multi-component exercise training regimen. Data are means ± SEM. In men, ANOVA revealed a significant main effect of exercise training (P < 0.01) and feeding (P < 0.01) but no significant exercise training by feeding interaction (P = 0.78). In women, ANOVA revealed a significant main effect of exercise training (P = 0.03) but no effect of feeding (P = 0.29) and no significant interaction (P = 0.51). ^aSignificant main effect of exercise training (P < 0.01). ^bSignificant main effect of exercise training (P < 0.05). ^cSignificant main effect of feeding (P < 0.01). * Value significantly different (P < 0.01) from corresponding value in older men (ANOVA and Tukey’s post-hoc testing on baseline – before exercise training – values only).

Figure 2

Exercise-induced increase in the basal, postabsorptive skeletal muscle protein fractional synthesis rate (FSR) after completing a 3-month multi-component exercise training regimen in men and women. Graphs show the median (central horizontal line), 25^th and 75^th percentiles (box), and minimum and maximum values (vertical lines). ^aValue significantly different from corresponding value in men (P < 0.05).