Muscle pain and injury as a cause of lameness and poor performance in the horse is poorly recognized.
Muscle injuries frequently cause lameness in human athletes and racing greyhounds. Similar injuries therefore would be expected in the horse.
The equine athlete is exposed to these predisposing factors on a routine basis. Hypothetically, if the horse suffers muscle strains, these injuries would most likely be manifested as lameness. The difficulty for the veterinarian is the positive diagnosis of these injuries. In human medicine, the athlete’s description of the pain location is often the single most important factor in diagnosis. This diagnostic aid is obviously lacking in veterinary medicine. Many of these cases probably go undiagnosed in equine medicine because they cannot be confirmed by commonly used diagnostic methods such as radiographs and nerve blocks. As such, these lamenesses are most likely treated empirically with various combinations of rest, analgesics, and anti-inflammatory agents.
Some veterinarians have recognized muscle injury as a cause of poor performance. Sites in the forelimb include the biceps brachii, brachiocephalicus, the pectorals and the musculotendinous junction of the superficial digital flexor. In the hindlimb, the semimembranosus and semitendinosus, adductor, gracillus, gluteal, and gastrocnemius muscle. Muscle tension, spasms and pain have been recognized in the thoracolumbar region. In fact, localized muscle soreness is readily induced by a poor fitting saddle or poorly balanced rider.
Source: Tracy A. Turner, DVM, MS