muscle fibers

​Fibre Type: Slow Oxidative (Type I) Characteristics

High oxidative capacity, slow contraction time, high resistance to fatigue, low force production, low glycolytic capacity, high capillary density.

Fibre Type: Slow Oxidative (Type I) Sporting Example

Endurance events, e.g., long-distance running.

Fibre Type: Fast Oxidative Glycolytic (Type IIa) Characteristics

High oxidative capacity, fast contraction time, medium resistance to fatigue, high force production, high glycolytic capacity, medium capillary density.

Fibre Type: Fast Oxidative Glycolytic (Type IIa) Sporting Example

Middle distance swimming, e.g., 400m.

Fibre Type: Fast Glycolytic (Type IIx) Characteristics

Low oxidative capacity, fastest contraction time, low resistance to fatigue, highest force production, high glycolytic capacity, low capillary density.

Fibre Type: Fast Glycolytic (Type IIx) Sporting Example

100m sprint.

The Size Principle (Henneman et al. 1974)

Smaller motor units (Slow Oxidative) are recruited first because they have a lower firing threshold; larger units are recruited last as intensity increases.

Spatial Summation

The recruitment of more/larger motor units to increase the strength of a muscular contraction.

Wave Summation

Increasing the frequency of nerve impulses to a muscle to increase contraction strength before the muscle can fully relax.

Tetanic Contraction

A sustained, powerful muscle contraction caused by impulses arriving so rapidly that no relaxation is possible.

Order of Muscle Fibre Recruitment

Slow Oxidative (I) -> Fast Oxidative Glycolytic (IIa) -> Fast Glycolytic (IIx).

Muscle Fibre Anatomy

Muscles are made of many fibres bound together. Key components include the Tendon, Endomysium, Myofibril, and Sarcomere.