Study summary · research use only
Ageing and local growth factors in muscle
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This review discusses local growth factors involved in skeletal muscle repair, adaptation, and aging, drawing on animal studies and human studies of muscle adaptation to strength training in older people. The authors describe how muscle responds to mechanical overload by increasing in size but atrophies with age, and how animal studies have shown older muscles repair less well after contraction-induced injury than young muscles. The review covers the growth hormone/IGF-1 axis, noting circulating hormone levels decline later in life while muscle tissue itself produces IGF-1 locally. It also discusses a muscle-specific IGF-1 isoform, mechano growth factor, and its proposed role in stimulating protein synthesis and satellite cell activity.
Abstract
Muscle responds to mechanical overload by increasing its size. In contrast, as a muscle gets older it atrophies. The mechanisms regulating these differing responses are not fully understood. Animal studies have shown that older muscles are less well able to repair following contraction-induced injury than young muscles. It is becoming clear that local growth factors produced within the muscle may play important roles in both repair, adaptation and ageing. The growth hormone/insulin like growth factor 1 (GH/IGF-I) axis is important during growth and development, but circulating levels of these hormones decline in later life. However, many tissues including muscle, produce IGF-I for autocrine and paracrine actions. Genetic manipulation of IGF-I in muscle has shown that it has considerable anabolic affects on muscle both in young and old animals. Insulin like growth factor 1 exists in multiple isoforms and one isoform, which differs from the systemic or liver type (IGF-IEa), appears to be particularly sensitive to mechanical signals and to muscle damage. This isoform (IGF-IEc) has been termed mechano growth factor (MGF). The anabolic actions of IGF-I and MGF are through stimulating protein synthesis and by playing a role in the activation, proliferation and differentiation of satellite cells. These effects are discussed in relation to human studies of muscle adaptation to strength training in older people who seem to retain an ability to increase muscle mass and strength through this type of exercise.
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