MUSCLE FIBRE TYPES

MUSCLE FIBRE TYPES and Their Properties

Basically if a stimulus is received by muscle cells (fibres) and it is great enough to cause a response – the fibres respond by contracting & relaxing (1st glimpse at “All or None principle”).

MUSCLE FIBRE TYPES and Their Properties

All muscle fibre types can operate at the same metabolic capabilities, but some are better biochemically equipped to work anaerobically or aerobically (without or with oxygen).

Anaerobic – activity of a high intensity that does not allow oxygen to be used in the metabolic process of ATP breakdown (e.g. maximal effort sprint 50m); if duration of activity of such an intensity continues, lactic acid is produced and build-up leads to fatigue (e.g. maximal effort 200m sprint)

Aerobic – activity of a lower intensity in which oxygen is used in the process of breaking down carbohydrates & fats for fuel source (e.g. 5 min + jogging)

Type 1

Slow-twitch fibres (ST) AEROBIC (with O2) Red in colour Type I (slow-oxidative) E.g. leg muscles

Type 2A and 2B

Fast-twitch (FT) ANAEROBIC (Without O2) White in colour Type IIa & IIb E.g. arm muscles

MUSCLE FIBRE TYPES and Their Properties

During the teen years, the number of ST and FT fibres become “fixed”; training can elicit some change, but for the most part, # of specific fibres & arrangement is pre-determined by genetics.

PROPERTIES OF MUSCLE FIBRES

CharacteristicTYPE I TYPE IIa TYPE IIb

Speed of contraction Slow Fast Fastest

Primary source of ATP O2 Glygogen- Glucose- LA

Phosphocreatine

Rate of fatigue Slow Intermediate Fast

# of mitochondria High Intermediate Low

Capillary density High Intermediate Low

Glycogen capacity Low Intermediate High

Fibre diameter Small Large Largest

Size of Motor Neuron Small Large Largest

Force Production Low High Highest

Oxidative Capacity High Intermediate Low

Activity used for Long Duration Short Duration Short Medium Duration