Day-to-Day Changes in Muscle Protein Synthesis in Recovery From Resistance, Aerobic, and High-Intensity Interval Exercise in Older Men

Background. Resistance exercise (RE) and aerobic exercise are recommended for older adults for fitness and strength. High-intensity interval exercise (HIIT) is an understudied but potent potential alternative to aerobic exercise. This study aimed to determine how each mode of exercise affected the integrated day-to-day response of muscle protein synthesis. Methods. Sedentary men (n = 22; 67 +/- 4 years; body mass index: 27.0 +/- 2.6 kg m(-2) [mean +/- SEM]) were randomly assigned to perform RE, aerobic exercise, or HIIT. Participants consumed a stable isotope tracer (D2O) for 9 days. Daily saliva samples were taken to measure tracer incorporation in body water. Muscle biopsies were obtained on Days 5-8 of D2O consumption to measure tracer incorporation into muscle at rest, 24 hours, and 48 hours following each exercise bout: RE (3 x 10 repetitions: leg extensor and press, 95% 10RM), HIIT (10 x 1 minute, 95% maximal heart rate [HRmax]), or aerobic exercise (30 minutes, 55%-60% HRmax). Results. Myofibrillar protein fractional synthetic rate was elevated, relative to rest, at 24 and 48 hours following RE and HIIT. The increase in myofibrillar fractional synthetic rate was greater following RE versus HIIT at both time points. HIIT was the only mode of exercise to increase sarcoplasmic protein fractional synthetic rate 24-hour postexercise (2.30 +/- 0.34% d(-1) vs 1.83 +/- 0.21% d(-1)). Conclusions. This study shows that in older men, changes in muscle protein synthesis in response to certain exercises are long lasting and that HIIT significantly increases myofibrillar and sarcoplasmic fractional synthetic rate in this population.