muscle fibre types

muscle fibre types

categories of muscle fibre adapted for various modes of use. Normally taken to refer to skeletal muscle unless specified otherwise. The main types found in stable human skeletal muscles after infancy are shown in the table. Intermediate 'hybrid' forms also occur, commonly in non-stable states such as during intensive or recently changed training regimes, or in recovery from injury. Types termed 1, 2A and 2B, containing myosins similarly designated, have been recognized since about 1970; however, the separate existence in many mammals of type 2X (initially also known as 2D), distinguishable from 2B only by sophisticated techniques, was recognized during the 1990s and it is now accepted that most, if not all, human fibres formerly called 2B in fact have 2X myosin. The slower-contracting muscles have a majority of type 1 fibres (typically approaching 90% in the extreme instance, soleus), while the faster-contracting ones have rather more, and often rather larger, type 2. Only some small specialist muscles (e.g. extraocular) have 80-85% fast fibres; in large limb muscles above 60% fast is reported only for sprint athletes. See also muscle enzymes. See table below .
Table 1: Characteristics of the three main types of stable human skeletal muscle fibres
Fibre type and myosin type12A2X (formerly '2B')
DescriptionSlow (-twitch) redFast (-twitch) redFast (-twitch) white
Principal energy supply systemOxidativeOxidative and glycolyticGlycolytic (anaerobic)
Abbreviated descriptionSOFOGFG
Mitochondrial densityHighMedium to very highLow
Motor neuron sizeSmallMediumLarge
Contraction speedSlowFairly fastFast
Fatigue resistanceHighMedium to highLow
Myosin ATPase activity after pH ∼ 10.3 pre-treatmentLowFairly highHigh
Ditto, after pH 4.6 pretreatmentHighLowMedium
Ditto, after pH 4.3 pretreatmentHighLowLow
References in periodicals archive ?
On the other hand, the proportion of muscle fibre types remained unaltered after 6 weeks of ballistic-power training but there was an increase in the CSA of the IIx muscle fibres by 36%.
Other physiological components such as body type, cardiovascular physiology and muscle fibre types should also be taken into account.
In view of the diseases affecting the frontal muscle and the lack of morphometric studies regarding the muscle fibre types and connective tissue sheaths comprising its belly, the objective of the present study was to quantitatively determine the area, diameter and relative volume of each fibre type (I, IIA and IIB), number of blood vessels per fibre and connective tissue (endomysium) area in these muscles obtained from a population of rabbits held in captivity.
Histochemical properties of muscle fibre types and activities in skeletal muscles of Standardbred trotters of different ages.
Section 2 was disappointing with the exception of Lexell's uniquely valuable studies on muscle fibre types.
The relationship between muscle fibre types and meat quality in pigs is inconsistent and not completely understood (Gentry et al.
Thus, the purpose of the present study was to describe the muscle fibre type composition, body composition and strength/power performance in well-trained hammer throwers.