1. Horses have three types of muscle: skeletal or striated or voluntary (for posture and moving); smooth or involuntary (e.g. in the airways and the gut) and cardiac (heart)
2. Locomotory muscles account for over 90% of the horse’s total muscle.
3. Locomotory muscles are made up of thousands of individual muscle cells, referred to as muscle fibres which are only a few centimetres long and fractions of a millimetre across.
4. Muscle fibres in locomotory muscles are broadly of two types: fast twitch and slow twitch. Slow twitch are primarily involved in posture whereas fast twitch are primarily involved in movement.
5. The diaphragm (breathing muscle) is actually a skeletal muscle.
6. The fast twitch fibres are further divided into two types: one type which is designed for stamina and is very good at using oxygen and another type which is developed for speed and strength.
7. The proportion of the slow and fast twitch fibres is different depending on where the muscle is and the area of the muscle.
8. The size of the muscle cells (fibres) can change with training. Speed and strength training makes the fibres bigger (which is why human sprinters look muscled) and stamina training makes the muscle fibres much thinner and the overall muscle smaller so it is easier for oxygen to get inside them (which is why human marathon runners look poorly muscled).
9. Forelimb muscles have more slow twitch fibres than hindlimb muscles.
10. Deep areas of a muscle have more slow twitch than superficial areas.
11. A fit Thoroughbred racehorse or fit Arabian endurance horse will have over half its bodyweight as muscle.
12. The middle gluteal muscle (the hindquarters) is one of the largest locomotory muscle groups. In a Thoroughbred this could be around 90% fast twitch fibres whereas in a Pony this might be around 80% and in a Heavy Hunter only 70% fast twitch fibres.
13. Locomotory muscle and heart muscle have a tremendous capacity to adapt to training.
14. Whilst the basic types of fibres in a muscle in an individual horse are determined by genetics, the way a muscle fibre behaves can be changed significantly by training.
15. A horse’s aerobic capacity (maximal ability to use oxygen) is determined by the genes for both the type of muscle (proportion of fast versus slow twitch fibres) and the size of the heart. It can also be increased by around 15% by training.
16. Each muscle is connected to hundreds of nerves. The smallest nerves fire first. The more nerves that fire, the more fibres that contract but there is never a situation in normal life when all the muscle fibres contract, even during flat out galloping or jumping.
17. Lactic acid is often blamed for muscle fatigue, but in fact, it is the lactic acid that allows horses to sprint. Without being able to produce lactic acid horses would be a lot slower.
We have lots of articles and information about equine muscles including:
- Article – The science behind equine muscle building supplements
- Webinar – Muscle Disease – Equine PSSM 1 & 2 and Myofibrillar Myopathy (MFM) by Stephanie Valberg
- Webinar – The Secrets of Equine Muscle Building by Dr David Marlin
- Survey – Muscle building poll
- Article – Vitamin E Supplements for Muscle Support Reviewed.