The Role and Regulation of Intramuscular Sex Hormones in Skeletal Muscle: A Systematic Review
Abstract
IntroductionSerum concentrations of androgens and oestrogens, the main male and female sex hormones, respectively, naturally fluctuate across the lifespan. Sex hormones are mainly produced in the gonads, but evidence suggests that they can also be locally synthesised in skeletal muscle. However, little is known about the purpose of intramuscular sex hormones biosynthesis and their role in skeletal muscle. This systematic review aimed to investigate 1) how intramuscular sex hormone levels vary across the lifespan, 2) whether intramuscular sex hormones are associated with skeletal muscle mass and function, and 3) whether exercise affects intramuscular sex hormone levels.
MethodsFour databases were searched, and studies were included if they contained measurements of intramuscular sex hormones from healthy males and females free from any hormonal treatment, from rodents, or from cultured muscle cells.
ResultsFifteen studies were included. Intramuscular testosterone was reduced in elderly males compared to their younger counterparts, but comparison of intramuscular sex hormone levels between pre- and postmenopausal females yielded inconclusive findings. Intramuscular androgens were positively associated with muscle mass and strength in males. In females, conflicting findings were reported for both oestradiol and androgens, and measures of muscle mass and function. Chronic exercise decreased androgens and oestradiol in females, but increased androgens in males. Acute exercise did not change intramuscular hormone levels in humans but increased them in rodents and cells.
ConclusionCurrent evidence suggests that ageing and exercise differentially modulate intramuscular sex hormone levels, and their association with muscle mass and function, between males and females.
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Research summary
The paper investigates the role of intramuscular sex hormones in skeletal muscle, particularly in the context of aging and exercise, which are relevant to understanding muscle health and function as we age. However, while it provides some insights into hormonal changes and their associations with muscle mass, the findings are largely incremental and do not address root causes of aging or propose significant interventions for lifespan extension. Thus, its impact on the field is solid but limited.
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