While exercise training causes some changes that will be easy for you to see, such as muscle development, other adaptations aren’t as readily apparent. Below is a summary of some of the changes that occur during exercise training and how environmental conditions affect them. Although this list isn’t comprehensive, it
will give you a good idea of some of the more important effects of exercise on your horse’s body.
Muscles and Tendons
Changes in muscle size and definition are two of the most easily identifiable adaptations to exercise, and they begin to occur at the molecular level within days of the first training session. Tendons, on the other hand, adapt more slowly to the increased demands placed on them by exercise. Several studies have suggested that tendons become thicker with exercise, but this response only occurs in certain tendons and happens over three or more months. This means that even though your horse’s muscles are getting bigger and stronger, his tendons aren’t necessarily keeping pace, and you’ll need to take extra care to keep them from being injured.
“Tendon and ligament injuries are most common when the animal is not in good physical shape,” says Robin Dabareiner, DVM, PhD, Dipl. ACVS, who studies equine lameness at the Texas A&M University College of Veterinary Medicine. “A key point to prevent injuries is to make sure the horse is fit enough for the activity you are performing.”>
Source : https://thehorse.com/170326/conditioning-horses-through-the-seasons-spring-and-summer/