Sarcopenia, which comes from the Greek words sarx (flesh) and penia (loss), refers to the process of age-related skeletal muscle loss. This term was advocated by Prof. Irwin Rosenberg in 1989. Sarcopenia occurs in all seniors regardless their health condition, as the muscle mass and strength will be lost naturally during aging process. When one's skeletal muscle mass and strength falls to an unhealthy range, he/she can be diagnosed as having sarcopenia.

We must understand the basic character of skeletal muscle before learning more about sarcopenia. Skeletal muscle governs our strength and power of movement. It attaches to both ends of the bone through a structure called tendon. The part of the muscle between both tendons is called muscle belly, which allows our contraction and relaxation and thereby lengthening and shortening of muscle. Skeletal muscle must act in a perfect harmony with bones for proper functioning of our musculoskeletal system, such that we can stand, walk, run, move around or even shake our bodies in the dance floor. For example, crawl, walk, climb etc. denote our movement during the stage of infant while the absence of movement is commonly found in the stage of death. Throughout our life cycle, some may lose movement due to various illnesses or even normal ageing process.

Skeletal muscle can be categorized into two broad types: Type I (slow twitch) and Type II (fast twitch). Type I fibers are responsible for the endurance and slowing down of muscle fatigue process. Role of Type II fibers is for short burst and power of motion, which will come to fatigue more easily.

Muscle size remained relatively constant in one's 30s and 40s. When it comes to their 50s, muscle size starts to decline noticeably. From the study, it was found that skeletal muscle decreases by approximately 6% per decade after the middle age. In other words, when someone reaches 85 years old, they will lose a quarter of the skeletal muscle they had when they were 45years old.

The loss of skeletal muscle mass and strength is more apparent in the lower extremities than the upper extremities. Due to our strong reliance on the musculature in the lower body to perform most daily activities such as walking, climbing stairs etc, this pattern of age related muscle loss is therefore of paramount implication on one's mobility , movement or related enjoyment. In the next article, we will further elaborate how to measure skeletal muscle mass.

Dr Liu Kin-wah
Specialist in Geriatric Medicine