Muscle Strain in Horses

What is Muscle Strain in Horses?

The equine body is made up of approximately 45-55% muscle, however muscular causes of poor performance and lameness are often underdiagnosed. Muscle strain in horses is the damage or breakdown of muscle and occurs most often in the large muscles of the hindlimb and back, and to a lesser extent in the neck and upper forelimb.

Symptoms of Muscle Strain in Horses

Clinical signs of muscle strain in horses include:

• Pain

• Heat radiating from injured muscle

• Swelling

• Stiffness

• Lameness

Causes of Muscle Strain in Horses

Equine athletes are requested to work hard and perform a variety of tasks and maneuvers. Muscle strains typically occurs either by an accident (fall or stepping the wrong way), or through a work-related injury, like overuse or untrained use.

Causes of work-related muscle strain include:

• Insufficient training

• Inadequate warm-up

• Exercising to fatigue

• Pre-existing lameness

Exercising in cold temperatures, which results in impaired circulation in the muscles, can also pre-dispose muscles to injury. Muscle injury tends to occur more frequently when horses are learning new tasks or activities their body is not used to.

Acute muscle strain is different from chronic inflammation. Chronic inflammation occurs after repetitive injury over time and can lead to fibrosis of injured muscles. Fibrotic myopathy is a well-characterized syndrome involving chronic injury to the semitendinosus and/or semimembranosus muscles. These are the large “hamstrings” on the back side of the hindlimbs in horses. Fibrotic myopathy is characterized by an altered gait where the stride is cut short and the leg jerks to the ground suddenly in the middle of the forward motion of the gait.

How Veterinarians Diagnose Muscle Strain in Horses

Diagnosing a muscle strain in horses starts with a thorough history, including any potential trauma, and details of the horse’s exercise routine. The diagnosis of a muscle strain can be difficult because the signs can be subtle and, in some cases, only present while the horse is in motion.

In order to localize the muscle strain, your veterinarian will start by assessing muscle symmetry and thorough palpation of the entire body. Running a blunt-tipped object down the back and behind the leg is often used to find an area of soreness. The horse should be observed at a walk, trot, and, if the horse is able, while lunging or while riding under saddle.

If the source of injury cannot be localized on physical exam and palpation, diagnostic tools like thermography, ultrasound, and bloodwork may be useful. Thermography detects surface temperature. If an area on the body is emitting more heat, it could indicate an area of inflammation. A cooler area on the body could be an area of decreased blood flow indicating chronic muscle atrophy. Once an area of muscle strain had been detected, ultrasonography can look at the localized area in more detail.

Treatment of Muscle Strain in Horses

Treatment of muscle strain typically involves reduced activity and short-term use of non-steroidal anti-inflammatories (NSAIDs) like flunixin meglumine or phenylbutazone.

If detected in the acute phase, ice therapy is useful to provide pain relief and reduce inflammation. Massaging the muscles is useful after the first 48 hours and helps relax the muscles, encourages blood flow, and helps prevent scar tissue from developing.

Severe muscle strain or tearing can also benefit from:

• Physical therapy

• Therapeutic ultrasound

• Cold laser

• Acupuncture

• Electromagnetic therapy

Shock wave therapy can be used to reduce pain, increase blood flow to the area, and accelerate healing.

The muscles that are most prone to muscle strain, like the hamstrings and back, are too large to be wrapped. Liniments like Sore No More, Magna Paste, and Absorbine can be useful to massage into these large muscle bellies. If the injury has caused secondary swelling that descends to the lower limbs, those areas may be wrapped with the same liniments. It is important to consult your veterinarian regarding any of these treatments. 

Recovery and Management of Muscle Strain in Horses

After recovering from a strained muscle, horses should be re-introduced to training and exercise gradually. A thorough warm-up routine that gradually increases in intensity toward the specific activity is vital.

For mild injuries, the prognosis for full return to work is favorable. However, it is more guarded for chronic or recurrent injuries. Some cases, especially chronic strains of the neck and back muscles, can lead to arthritis in the vertebral column.

Exertional Rhabdomyolysis or “tying-up” is a syndrome that involves severe muscle injury and breakdown. Horses that are prone to this syndrome are managed with diet, vitamins E and selenium, electrolytes, and a specific exercise regimen.

Prevention of Muscle Strain in Horses

The most important thing you can do to help prevent muscle strain is to make sure your horse is adequately warmed up prior to working—this is critical in cold temperatures.

Another good prevention is to ensure you have an adequate stretching routine for your horse. Walking your horse in a long and low frame is a good way to loosen up the large muscles. Adding cavalettis, walking over ground poles, and bending or carrot stretching are also particularly beneficial. 

Having a proper saddle-fit is imperative to prevent tension in the back which could lead to a muscle strain. Additionally, a balanced, healthy hoof will also help prevent muscle strains by giving the horse symmetry as well as preventing strains related to trips and falls.