Researchers measured the way muscle genes are switched on and off when a Thoroughbred exercises and found that these genes work together to adapt to exercise training.

"As any trainer knows, different muscles respond and adapt to training in different ways," said Beatrice A. McGivney, PhD, of the University of Dublin in Ireland. "A person who is a long distance runner and another person who is a weight lifter do a lot of exercise, but their muscles respond differently and look differently. We have previously identified the genes that are required for normal functioning muscle in horses. Following this, we looked at what genes are switched on or off following training."

While every cell in a horse contains the same genes inherited from the sire and the dam, only the genes required in a specific tissue are expressed (turned on) in that particular tissue. For example, there are genes specifically associated with eye function that are expressed in the eye. Similarly, there are genes that are only switched on in muscle tissue.

"In addition, specific genes are also turned on and off under different physiological conditions–for example, during exercise," McGivney said