Skeleton and movement: a body built to travel

A frame that carries power forward

In the Royal Veterinary College's description of the horse's "power train", the lungs and heart deliver oxygen to the muscles, which burn it to create the power that drives the skeleton. The skeleton is the frame all that power works through.

Much of the push comes from behind. A Royal Veterinary College study of back movement describes the vertebral column and its muscles as fundamental to movement, carrying force from the hind legs through to the forelegs, neck and head. Because everything is connected, a problem in one place affects others: lameness or pain, such as from a badly fitting saddle, can load the spine unevenly and change how the muscles of the back and trunk work.

Points of the horse

Riders and vets describe the outside of the horse with a set of names called the points of the horse. The British Horse Society's riding-award guidance lists these, among others:

The anatomy hub has an interactive diagram showing where they are.

Feel the skeleton for yourself

You can feel a surprising amount of the skeleton through the skin. In fact, that is how the British Horse Society's fat-scoring method works: you run your hands over key landmarks and judge how much fat covers them. A healthy fat covering is a score of 2.5–3 out of 5, unless your vet advises otherwise. On a horse in healthy condition:

• Neck. You should be able to feel the nuchal ligament along the length of the neck, near the top of the mane. It feels "like a ball of elastic bands". Muscle lies below it; any excess fat sits above it. Stallions naturally develop a crest because of their hormones.
• Shoulder. Run your hand down the neck: it should be stopped by the shoulder blade, which should be clearly defined, rather than sliding smoothly over fat.
• Ribs. You should be able to feel the ribs easily with light pressure, but not see them.
• Back. About a hand's width from the withers, your hand should follow the arch over the spine and feel the backbone. Fat on either side of the spine can build up into a gutter.
• Hindquarters. You should be able to see and feel the hip bones, the top of the pelvis and the tail head under a thin layer of fat. From behind, the quarters should be gently rounded, like the letter C.

The British Horse Society suggests fat scoring every two weeks, alongside a weigh tape. Be gentle feeling the neck of a horse carrying excess fat, as the area can be sore.

The legs

One toe on each foot

A horse stands on the tip of a single toe on each foot: its original third toe, encased in the hoof. The University of Bristol explains that the upper parts of the ancestral side toes survive as the splint bones, fused alongside the central cannon bone, while the lower parts have been lost completely.

Inside the hoof are the pedal bone (or coffin bone) and the small navicular bone behind it. The joint between the pedal bone and the short pastern bone is the coffin joint, which plays a key role in movement and weight-bearing. See Inside the hoof for the whole foot.

The hock

The hock is a set of joints between several small tarsal bones. The lower three are the proximal intertarsal, distal intertarsal and tarsometatarsal joints. The University of Edinburgh's Dick Vet Equine Practice explains that bone spavin, osteoarthritis of the hock, usually affects the lowest two of these and most often affects teenage and older horses. Conformation that loads the hocks unevenly, such as sickle hocks, cow hocks or being "in at the hocks", makes it more likely, as can poor trimming or shoeing.

Built for endurance

Why does a horse's leg look the way it does? University of Bristol palaeobiologists argue that it evolved for endurance rather than speed. The key innovation was the "spring foot", which stores elastic energy in the tendons of the leg with each stride. It evolved in three-toed ancestors around 20 million years ago, as grasslands spread across North America.

As the single-toed lineage evolved, the bones of the central toe strengthened the spring-foot apparatus, while the back became shorter and stiffer. A stiff back doesn't suit the back-flexing gallop. So the researchers propose that these horses relied on the energy-efficient, medium-speed trot to roam widely for food and water. Single-toed horses appeared in North America around 12 million years ago. The genus Equus, which includes modern horses, appeared by about five million years ago. By a million years ago, all three-toed horses were extinct.

When bones break

World Horse Welfare says the most common sites for fractures are in the lower leg: from the knee down, or from the hock down. The neck vertebrae of young horses and the pelvis of horses doing a lot of fast work are also vulnerable. Fractures can happen in an accident or build up over time from repeated concussion (stress fractures). Neck and spine fractures can press on the spinal cord or nerves and cause neurological signs.

To build strong bones, World Horse Welfare advises giving young horses a well-balanced diet, experience of different ground surfaces, and short but repeated spells of low-level concussive exercise from a young age. That exercise shouldn't be excessive, and once a horse is in work it should be part of a structured training programme. Stable field groups also help, because they reduce kicking.

The back and the saddle

A horse's shape changes with its fitness. The British Horse Society says the area under the saddle can change dramatically after as little as four to six weeks of regular ridden work, so check the saddle fit before and during a fitness programme. At the start of a fitness programme a horse's back is weaker and more prone to injury. Pain in the back or elsewhere may show as resistance, bucking, tail clamping or reluctance to go forward.