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 massCriterion 2 - low muscle strengthCriterion 3 - low physical performance
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