Exercise associated myopathies (Proceedings)
Exertional rhabdomyolysis is muscle necrosis precipitated by exercise or exertion, resulting in myoglobinuria, elevated serum CK (usually > 5,000 in acute cases) and/or elevated AST in animals with normal liver function.
Local Muscle Strain
Muscle strain may be induced by inadequate warm-up, pre-existing lameness, exercise to the point of fatigue and insufficient training. The lumbar and gluteal muscles are frequently injured in jumpers, dressage and harness horses and the semimembranosus and semitendinosus muscles are more frequently damaged in working Quarter Horses performing abrupt turns and sliding stops (and may also occur secondary to intramuscular injections in this region). The gracilis muscle (adductor) can be torn through misadventure and creates swelling and pain in the medial thigh, and elevated serum CK.Diagnosis: History, altered stride and reluctance to engage the hind quarters, and pain or heat on deep palpation of the muscles. CK and AST are usually only mildly elevated and thermography may assist with identification of affected muscle groups. Severe muscle trauma may be identifiable on ultrasound. In horses with chronic damage to the semimembranosus and semitendinosus, fibrotic myopathy may occur resulting in a characteristic gait.
Treatment: Rest and non-steroidal anti-inflammatory medication. Hand walking once the initial stiffness has dissipated. Rehabilitation: icing for acute injuries, therapeutic ultrasound, massage and stretching. Resume exercise gradually with appropriate warm-up. Check saddle for fit. If treating fibrotic myopathy surgical procedures can be tried (tenotomy of the tibial insertion of the semimembranosus tendon and/or transection (± excision) of the fibrotic area of muscle).
Exertional Rhabdomyolysis "Tying Up"
Exertional rhabdomyolysis represents a pathological description of a number of muscle diseases which have common clinical signs.
A useful way to classify tying-up is the following:
1. Sporadic Exertional Rhabdomyolysis
2. Chronic Exertional Rhabdomyolysis