There are three types of muscles in the horse's body. These are known as type I, type IIA and type IIB. Each muscle type has varying factors that differentiate them. These include:
- Aerobic or anaerobic capacity
- How quickly the muscle contracts and relaxes
- Muscle diameter
Type I Muscle Fibres
The first type of muscle fibre is known as ‘red endurance muscle’. They are a more red colour due to their higher capillary supply to provide the fibres with adequate oxygen.
These muscles are slow to contract and relax. They have a narrow diameter and due to this, cannot result in the same amount of power as either of the type II fibres. The narrower diameter does however cause these fibres to respond to a lower level of stimuli than is required for other fibre types. This means that it takes less to gain a response from these muscle fibres.
Type I muscle fibres are utilised for long bouts of low intensity exercise. Consequently, a horse that has a high proportion of type I muscle fibres will be genetically predisposed to perform over longer distances. Such a horse may be well suited to endurance work.
Type II Muscle Fibres
These fibres are known as ‘white sprint muscle’. They are more powerful but are less resistant to fatigue than type I muscle fibres. Type IIA fibres contract four times as quickly as type I muscle fibres, whilst type IIB fibres contract ten times as quickly, giving an indication of why these muscle fibre types are more powerful.
Type IIA fibres are recognised as having qualities that sit between types I and IIB. Type IIB muscle fibres are recognised as the truly sprint muscle fibre types. Both type II fibres are more white in colour, not needing to rely on a good oxygen supply to generate ATP for energy production.
Horses aren’t born with one muscle type only. They do however tend to have a proportionally larger amount of a particular muscle type, which can predispose a horse to performing well in a certain area. It is these different muscle types that can often recognise a horse as a sprinter or stayer, based purely on their muscular conformation.
Factors Affecting Performance in the Equine
Muscles shouldn’t be the sole consideration for a horse’s performance capabilities. Obviously training and nutrition will also play important roles in the likelihood of a horse’s success in any given field. These should not be overlooked when it comes to training and preparing a horse for any discipline.
Source
- Equine Exercise Physiology, Marlin, D., and Nankervis, K. Blackwell Publishing 2002. ISBN 0 632 05552 9.
Chris Thomas - C. Thomas has studied and worked with horses since 2001. She teaches horse studies part time and is undertaking an Equine Science ...
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