Swimming is unsuitable for training Thoroughbred racehorses but is suitable for endurance horses. The reason swimming is an excellent exercise for endurance rather than racehorses is that swimming addresses the slow twitch muscle fibres. A horse cannot be trained for both endurance and outright speed because each type of training has an opposite effect on muscle fibres.
Horses have two distinctly different types of muscle fibre types: slow twitch and fast twitch (depending on their contraction times). The slow twitch fibres are designed for endurance and use oxygen. The fast twitch fibres produce speed, and their energy is obtained through anaerobic pathways. They have very limited endurance capacity.
Long slow work conditions the slow twitch fibres (Type 1) which use aerobic pathways. Arabian horses have a far higher proportion of slow twitch fibres than other breeds of horses. Thoroughbred racehorses have a high proportion of fast twitch fibres. Slow twitch fibres operate on oxygen only and are endurance muscles, able to operate for very long periods without fatigue. Type II fast twitch fibres can be trained either for stamina or for speed. A training program which trains the fibres for the wrong energy pathways clearly will reduce performance significantly.
As swimming for training addresses only the slow twitch muscle fibres, it should not be used for racehorses unless swimming races are introduced one day! Research has also shown that swimming must be avoided in the case of a racehorse which is a ‘bleeder’. When a horse is swimming, it is harder for them to breathe as most of their chest is submerged. It’s not wise to make the lungs of a ‘bleeder’ work harder in this way.
However, swimming is excellent training for endurance horses for the cardiovascular system and does not place stress on legs, muscles and tendons. Scientific studies have shown that swimming is a strenuous exercise. Three minutes of swimming is said to be equivalent to 1 mile (1,600 metres) of steady harness or ridden work. Swimming is an excellent conditioning procedure because it provides a hard workout while avoiding injury to a horse’s legs, and for this reason, several leading endurance trainers have included swimming as a supplement to their training routines.