GH/IGF-I axis and matrix adaptation of the musculotendinous tissue to exercise in humans.
Level 5 - mechanism / opinion, no new human data
Narrative review of human physiological and mechanistic literature without systematic search methodology
PubMed 22429205 · doi:10.1111/j.1600-0838.2012.01459.x
What was done
Narrative review summarizing findings from human studies regarding the role of the systemic growth hormone/insulin-like growth factor I (GH/IGF-I) axis and local IGF-I expression in the adaptation of musculotendinous tissue to exercise. The review examines evidence from pathological hyper-GH/IGF-I states, multi-week GH administration trials, and acute local IGF-I injections into connective tissue.
What was found
No numerical data, sample sizes, or effect estimates were reported in the abstract. Qualitatively, elevated GH/IGF-I levels (pathological, systemic GH administration, or local IGF-I injection) were associated with increased collagen expression and synthesis in muscle and tendon connective tissue, an effect described as far more potent than any effect on contractile muscle proteins. GH/IGF-I also increased skeletal muscle satellite cell counts despite no change in myofibrillar protein synthesis. Finally, the authors note there is no direct evidence establishing that age-related musculotendinous decline (sarcopenia and tendon degradation) is caused by reduced GH/IGF-I activity.
Why it matters
The review clarifies that the primary target of GH/IGF-I in human musculoskeletal tissue is connective tissue remodeling and collagen synthesis rather than direct myofibrillar hypertrophy.
Limits
The abstract provides no quantitative data, effect sizes, or study counts. As a narrative review, it lacks systematic search methodology and is vulnerable to selection bias. The discussed associations do not prove a causal role for declining GH/IGF-I in age-related sarcopenia or tendon deterioration.
Cited by
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