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Principal Body System: Muscular

Definition: Specifically refers to skeletal muscle tissue

Function: Participates in bringing about movement; maintains posture; produces heat

There's muscle, and there's muscle. We've got muscle tissue, which refers to all the contractile tissues of the body, cardiac muscle (part of the cardiovascular system) and smooth muscle (part of the relevant system, i.e. digestive or urinary).

The muscular system, however, refers to the skeletal tissues that make up individual muscle organs, and that's what we're talking about on this page, as this tends to be what us horse-people are concerned with. As in, how they make the equine body move, or not, as the case may be. And when you think how huge the equine skeleton is, with every single bone covered in a muscle, that's a whole lot of muscle.

To quote Dr Eleanor Kellon, "Muscle is the engine which drives all types of work. Skeletal muscle makes up an average of 45% of the weight of a horse with a normal body condition score, which is even more than bone. In addition to initiating movement, implementing fine motor-control of intricate manoeuvres and controlling speed, muscle stabilises and protects the skeleton and joints."

Keeping our horses' muscles healthy

I don't think any of us would disagree that equids have evolved to move, sometimes many miles each day, and no doubt most of us, if not all, know that a sedentary or box-rest horse is not in a healthy muscular state at all.

Muscles respond to exercise, simple as that, both during and after a workout. Exercise improves muscle strength, speed, power and endurance, and changes start to happen with resistance exercise; this means that the workout must be greater than what the body typically does during the day, which activiates the process of muscle building, aka hypertrophy.

However ... top tip - too much intensity and you’re looking at trauma to muscle fibres, resulting in small microscopic tears in the tissue – the severity of the tear depends on the intensity of the activity. These fibres are bundled together into fascicles. Individual fibres are cross-linked so they slide inside the fascicle. Near the end of each muscle these fibres turn into tendon and then attach to bone. Damage develops when a muscle or tendon is overstretched, pulling the fibres apart and losing the ability to adequately contract.

Here are several factors which can contribute to an increased risk of injury:

  • Lack of conditioning - this can leave muscles weak and more likely to sustain an injury from low degrees of force.
  • Fatigue - muscles that have been worked to fatigue are less likely to provide good support to the joints.
  • Tight muscles - improper warmup or lack of stretching reduces range of motion in the joint and makes the muscles prone to trauma and tears. Properly warming up before activity helps to loosen muscles and increases range of motion.
  • Environmental conditions - slippery, uneven surfaces may increase the risk of injury, i.e. sloped surfaces can increase the risk of muscle strain as one leg is hitting the surface lower than the other leg due to the slope.

But all is not lost - the damaged muscle tissue activates satellite cells which rush to the damaged area to replicate and fuse to the torn fibres. This process forms new muscle protein strands which increases the strength and and size of the muscle, resulting in overall muscle growth.

In human-world, exercising specific muscles regularly can increase their size by up to an astonishing 60%, but we're not talking about our own gym membership here, nor can I see our horses heading to a Body Pump class. With our horses it's more about coordination and control rather than physical power and strength, but still on a frequent basis, as this leads to improved muscle coordination which trains muscles to work efficiently together.

Long term, regular exercise increases blood supply to the muscles which improves the delivery of nutrients, minerals and vitamins to the muscles, which makes them able to regenerate after injury or exercise more efficiently. Plus, after regular exercise muscles can store large amounts of glycogen for energy. Size and quantity of the muscle cells’ mitochondria (the power source of each cell) also increase, which also results in an increased rate of energy production.

Active muscles deal with food energy from glucose and fat very efficiently, with enzymes involved in energy production becoming more efficient with enhanced metabolism response. The long and short of it all? Regular resistance exercise leads to healthy musculoskeletal function.


Now for the big one. Everything I've said above relates to that mysterious Perfect World. However, there's a (not to put too fine a word on it) challenging condition that's becoming all the more prevalent out there - PSSM.

As wiki describes it, "Equine polysaccharide storage myopathy (EPSM, PSSM, EPSSM) is an inheritable glycogen storage disease of horses that causes exertional rhabdomyolysis (the destruction of striated muscle cells; azoturia). It is most commonly associated with heavy horse breeds and the American Quarter Horse. While incurable, PSSM can be managed with appropriate diet and exercise."

I can't claim to have my own personal experience with a PSSM horse. However, in 2014 I had my first client, Samantha, who contacted me with her PSSM horse, Star, followed by Sarah and her horse Splodge, and since then, several more. Thanks to Samantha and Sarah, together over the years we've immersed ourselves in trying to fathom this extraordinarily complex and fragile equine syndrome.

Whilst not finding that elusive 'cure', we have a bit of an understanding of PSSM. After considerable research we've put together our take on PSSM, so if you've recently been given the PSSM diagnosis or you're struggling with which direction to follow, I can't say we're the oracle of all things PSSM, but our dedicated page (image link below) may help guide you with some food for thought.

Meanwhile, there are a couple of excellent Facebook pages packed full of information, latest updates and client stories. Both Samantha and Sarah are regulars on the page.

PSSM Forum - https://www.facebook.com/groups/202978353056065/

PSSM Forum & 5 Panel Genetic Testing & Discussion - https://www.facebook.com/groups/432915936807292/

PSSM UK - https://www.facebook.com/groups/420056078181332/