Age-related differences in the dose-response relationship of muscle protein synthesis to resistance exercise in young and old men.
Level 3 - non-randomized controlled study
Non-randomized comparative physiological cohort study between two age groups
PubMed 19001042 · doi:10.1113/jphysiol.2008.164483
What was done
Researchers evaluated myofibrillar protein synthesis (MPS) and anabolic signalling pathways in response to resistance exercise across intensities ranging from 20% to 90% of 1 repetition maximum (1 RM). The study compared two groups of post-absorptive, healthy men with identical body mass indices (24 +/- 2 kg/m2): 25 young men (24 +/- 6 years) and 25 older men (70 +/- 5 years). Vastus lateralis muscle was sampled before, immediately after, and at 1, 2, and 4 h post-exercise. MPS was measured by incorporation of [1,2-(13)C] leucine; phosphorylation of p70s6K and 4EBP1 was measured using Western analysis.
What was found
Both groups showed a sigmoidal dose-response relationship between MPS at 1-2 h post-exercise and exercise intensity, which plateaued at 60-90% 1 RM but was blunted in older men (P < 0.05). At all intensities, MPS fell to near-basal values by 2-4 h post-exercise in both groups. Phosphorylation of p70s6K and 4EBP1 at 60-90% 1 RM was blunted in older men. At 1 h post-exercise at 60-90% 1 RM, p70s6K phosphorylation predicted MPS at 1-2 h post-exercise in young men but not in old men. Absolute numerical values for MPS were not reported in the abstract.
Why it matters
This study demonstrates that aging is associated with anabolic resistance of muscle protein synthesis and intracellular signalling across a range of resistance exercise intensities.
Limits
The study was restricted to 50 healthy men (25 per group) and excluded women and clinical populations. Measurements were only conducted in the fasted (post-absorptive) state over an acute 4-hour post-exercise window, without evaluating feeding or chronic training adaptations.
Cited by
- supports Older adults exhibit anabolic resistance to an acute bout of resistance exercise across a wide range of load spectrums.