Resistance exercise acutely increases MHC and mixed muscle protein synthesis rates in 78-84 and 23-32 yr olds

We determined whether shortterm weight-lifting exercise increases the synth esis rate of the major contractile proteins, myosin heavy chain (MHC), acti n, and mixed muscle proteins in nonfrail elders and younger women and men. Fractional synthesis rates of mixed, MHC, and actin proteins were determine d in seven healthy sedentary 23- to 32-yr-old and seven healthy 78- to 84-y r-old participants in paired studies done before and at the end of a 2-wk w eight-lifting program. The in vivo rate of incorporation of 1-[C-13]leucine into vastus lateralis MHC, actin, and mixed proteins was determined using a 14-h constant intravenous infusion of 1-[C-13]leucine. Before exercise, t he mixed and MHC fractional synthetic rates were lower in the older than in the younger participants (P less than or equal to 0.04). Baseline actin pr otein synthesis rates were similar in the two groups (P = not significant). Over a 2-wk period, participants completed ten 1- to 1.5-h weight-lifting exercise sessions: 2-3 sets per day of 9 exercises, 8-12 repetitions per se t, at 60-90% of maximum voluntary muscle strength. At the end of exercise, MHC and mixed protein synthetic rates increased in the younger (88 and 121% ) and older participants (105 and 182%; P < 0.001 vs. baseline). These find ings indicate that MHC and mixed protein synthesis rates are reduced more t han actin in advanced age. Similar to that of 23-32yr olds, the vastus late ralis muscle in 78-84 yr olds retains the capacity to increase MHC and mixe d protein synthesis rates in response to short-term resistance exercise.