The Tanner Hill - Wellness

You may not know that the role of skeletal muscle is not confined to movement. In fact, it has recently been regarded as an endocrine organ. The endocrine system is constituted by different endocrine organs, and it is a system of endocrine glands (such as the thyroid in your neck), each of which secretes a type of hormone directly into the bloodstream to regulate the body. The muscle also produces and releases cytokines which are signalling molecules used extensively in communications between cells. Think of it as letter or email in our daily life as a way to connect with people. These kinds of cytokines (or myokines secreted by skeletal muscle) are produced in response to muscle contraction, which subsequently can influence metabolism in other tissues and organs.

Why Exercises are Good for Us

These myokines are important in harmonising the advantages of exercises, and they explain why we have long been educated on the benefits of regular daily exercises since primary school – the myokines play a paramount role in the protection against diseases such as heart disease, diabetes and cancer. Furthermore, exercising can also alter the function and metabolism in other organs such as fat tissue, liver and brain, which come as no surprise then, that exercise may be regarded as a form of therapy or treatment in certain conditions in terms of endurance training or strength reconditioning. With recent findings showing that exercises induce anti-inflammatory effects in action, hence protecting against chronic illness associated with low-grade inflammation, you can regulate your physical health by doing adequate amount of suitable exercises.

How Hormonal Balance Affects Muscle Growth

On the other hand, endocrine factors also have a role to play in muscle growth and development throughout one's life-cycle. It is important to note that certain types of hormonal excess or deficiency can greatly affect both muscle structure and function. In older adults, for instance, anabolic hormones decrease while catabolic hormones increase. Anabolic hormone is mainly responsible for protein production and therefore the promotion of tissue growth (e.g. muscle building). Catabolic is the opposite of anabolic, which means catabolic hormones cause cellular loss and damage; and it contributes to the muscle breakdown for energy production when we are under stress.

Hormonal Levels and Sarcopenia

What we know for now is that the reduction in sex hormone levels is associated with sarcopenia. The fall in male hormone (or testosterone) is related to the decline in muscle mass, muscle strength and functional status. Meanwhile, the female sex hormone (or oestrogen) would also drop after menopause, which can directly affect muscle-building. Since both oestrogen and testosterone inhibit the production of catabolic cytokines or messengers, the loss of these hormones with age could have both direct and indirect effects on muscle breakdown. Thus, studies had been done to see the effects of replacement of these hormones as we age.

Growth Hormone (GH) shows a tendency to decline with age, and the secretion of GH is impaired in elderly men and women. GH usually stimulates growth during childhood and adolescence, and it is required for the maintenance of muscle and bone in adulthood. GH exerts most of its anabolic action through insulin growth factor 1 (IGF-1). The structure of IGF-1 is similar to insulin. Usually, IGF-1 increases at puberty and then progressively declines with age. In fact, the levels of IGF-1 and GH go hand in hand, as IGF-1 also has a similar lowering trend as GH when we age. Physical exercises may enhance level of IGF-1. It plays a pivotal role in skeletal muscle hypertrophy and atrophy through the promotion of protein production, as well as inhibition of protein degradation, which contributes to the development of sarcopenia in senior citizen.

Now that you know the causes and effects of different hormones on muscle-building and breakdown, and why you should take your regular daily exercises seriously. By understanding the additional role of muscle, we can learn to best tackle sarcopenia.

Dr Liu Kin-wah, Specialist in Geriatric Medicine