Exercise Plus Presleep Protein Ingestion Increases Overnight Muscle Connective Tissue Protein Synthesis Rates in Healthy Older Men.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 33588378 · doi:10.1123/ijsnem.2020-0222
What was done
Thirty-six healthy older men were randomly assigned to one of three groups (n = 12 each): ingestion of a nonprotein placebo before sleep (PLA), ingestion of 40 g of intrinsically labeled casein protein before sleep (PRO), or a single evening bout of resistance exercise followed by 40 g of presleep intrinsically labeled casein protein (EX+PRO). Stable isotope tracer infusions (L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine) alongside blood and muscle tissue sampling were performed across overnight sleep to assess muscle connective tissue protein synthesis rates and dietary amino acid incorporation.
What was found
Presleep protein alone did not significantly increase overnight muscle connective tissue protein synthesis rates compared to placebo (0.060 ± 0.024%/hr in PRO vs. 0.049 ± 0.013%/hr in PLA; p = .73). In contrast, EX+PRO resulted in higher synthesis rates (0.095 ± 0.022%/hr) compared with both PLA and PRO (p < .01). Furthermore, prior exercise increased the incorporation of dietary protein-derived amino acids into muscle connective tissue protein (0.054 ± 0.009 mole percent excess in EX+PRO vs. 0.036 ± 0.013 in PRO; p < .01).
Why it matters
These findings demonstrate that presleep protein ingestion alone is insufficient to stimulate overnight muscle connective tissue protein synthesis in older adults, but combining prior resistance exercise with presleep protein effectively promotes connective tissue remodeling during sleep.
Limits
The study was restricted to a small cohort of healthy older men, limiting generalizability to women, younger individuals, or clinical populations. It measured only acute, single-night synthetic responses rather than long-term structural adaptations, and it lacked an exercise-only comparator group without protein.
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- supports Performing exercise with a specific limb directs a greater proportion of ingested dietary amino acids into that exercised muscle compared to non-exercised muscle.