Concurrent resistance and aerobic exercise stimulates both myofibrillar and mitochondrial protein synthesis in sedentary middle-aged men.
Level 2 - randomized trial
Randomized crossover physiological trial in humans
PubMed 22492939 · doi:10.1152/japplphysiol.00166.2012
What was done
Eight sedentary middle-aged men (age 53.3 ± 1.8 yr, BMI 29.4 ± 1.4 kg/m²) completed three exercise trials in randomized order: resistance exercise (RE: 8 × 8 leg extensions at 70% 1RM), aerobic exercise (AE: 40 min cycling at 55% peak power), or concurrent exercise (CE: 50% volume of RE followed by 50% volume of AE). Participants consumed 20 g of protein post-exercise. Muscle biopsies with a primed, continuous L-[ring-¹³C₆]phenylalanine infusion were obtained while fasted, and at 1 h and 4 h post-exercise to measure myofibrillar and mitochondrial fractional synthesis rates (FSR), signaling phosphorylation, and mRNA expression.
What was found
All conditions increased mitochondrial FSR above fasted rates (RE: 1.3-fold; AE: 1.5-fold; CE: 1.4-fold; P < 0.05). Only CE (2.2-fold) and RE (1.8-fold) increased myofibrillar FSR (P < 0.05). At 1 h post-exercise, Akt phosphorylation increased at Ser473 (CE: 7.7-fold; RE: 4.6-fold) and Thr308 (CE: 4.4-fold; RE: 2.9-fold), with CE greater than AE (P < 0.05). PRAS40 Thr246 phosphorylation increased in CE (3.8-fold) and AE (2.5-fold; CE > RE, P < 0.05). mTOR Ser2448 phosphorylation remained unchanged (P > 0.05), whereas rpS6 Ser235/236 phosphorylation increased only after RE (10.4-fold, P < 0.05). PGC-1α expression increased at 1 h (CE: 2.9-fold; AE: 2.8-fold) and 4 h (CE: 2.6-fold; AE: 2.4-fold), and PGC-1β increased at 4 h (CE: 2.1-fold; AE: 2.6-fold) (all P < 0.05).
Why it matters
This study demonstrates that performing a combined session of resistance and aerobic exercise acutely stimulates both contractile and mitochondrial protein synthesis pathways without mutual interference in sedentary middle-aged men.
Limits
The sample size was very small (n = 8) and restricted exclusively to sedentary middle-aged men, limiting generalizability to women, trained athletes, or older individuals. Measurements were confined to acute 4-hour post-exercise responses, which may not directly correlate with long-term training adaptations such as muscle hypertrophy or endurance gains.
Cited by
- supports Traditional resistance exercises like squats produce greater gains in muscle protein synthesis with substantially less volume of work compared to cycling.