Ageing and Physiological Change in Muscle

As people age the following physiological changes are observed in muscle;

An increase in fat and connective tissue

A decrease in protein synthesis

A decrease in total muscle cross-sectional area

Loss of maximum isometric contraction force

Decreased endurance capacity

In relation to muscle fibres the faster-contracting type II fibres decrease at a greater rate than type I fibres, such that over time type I fibres greatly outnumber type II fibres

It is thought that these age-related changes occur due to:

1 Reduced blood flow to muscles due to decreased capillary density (making less O2 available to exercising muscles)

2 A decrease in aerobic enzymes resulting in mitochondrial decay

3 Increased mitochondrial DNA deletions and mutations

Ageing and Change in Muscle Strength

The age-related changes in muscle result in reduced muscle strength. This process begins at age 30 with a subsequent reduction in strength of 8% per decade. The rate of decrease is similar in men and women and affects muscle strength more in the legs than in the arms. By the age of 70, there is a 20 - 40% decrease in maximal isometric strength which impacts sustainable walking speed.

These graphs show the change in muscle area, strength and aerobic capacity with age

Sarcopenia

Sarcopenia can be defined as loss of skeletal muscle mass and function as a result of ageing

Diagnosis of Sarcopenia

The European consensus for the diagnosis of sarcopenia requires documentation of criterion 1 and either criterion 2 or 3. Criterion 1 - low muscle mass Criterion 2 - low muscle strength Criterion 3 - low physical performance