Molecular attributes of human skeletal muscle at rest and after unaccustomed exercise: an age comparison.

The current study examined muscle DNA and protein concentrations ([ ]) and the [RNA] (assumed to represent translational capacity), [RNA]:[DNA] (assumed to represent transcriptional efficiency) and [protein]:[RNA] (assumed to represent translational efficiency) in younger vs. older participants during a resting state. Further, changes in muscle [DNA], translational capacity, and transcriptional efficiency were analyzed 24 hours after an unaccustomed resistance exercise bout. Younger (20.9 +/- 0.5 years, 84.0 +/- 5.2 kg, 26.6 +/- 1.8 kg x m(-2); n = 13) and older men (67.6 +/- 1.3 years, 88.7 +/- 4.8 kg, 28.6 +/- 1.4 kg x m(-2); n = 13) reported to the laboratory and completed an unaccustomed bout of lower-body resistance training (i.e., 3 sets of 10 repetitions at 80% 1 repetition maximum for Smith squat, leg press, and leg extensions). Muscle biopsies from the vastus lateralis were obtained before and 24 hours after exercise. Baseline [RNA], [DNA], [protein], and [RNA]:[DNA] were not different between age groups (p > 0.05). Baseline [protein]:[RNA] was greater in younger vs. older men (p = 0.045), whereas 24-hour postexercise [RNA]:[DNA] tended to be greater in older men (p = 0.087). These findings suggest that a decrease in the efficiency of translational processes occurs in older human skeletal muscle, whereas global transcriptional processes appear to be unaltered when compared with those in younger men. In lieu of these data, it remains apparent that muscle-protein synthesis is impaired in aging skeletal muscle and effective countermeasures such as resistance exercise and nutritional adequacy must be undertaken by older populations to offset this phenomenon.