Physiological effects of training The skeletal system

Points of the horse

Structure of the lower limb

Structure of the underside of the hoof

The equine skeletal system The musculoskeletal system is made up of skeletal muscle, bone & other connective tissues: – Cartilage; – Ligaments; – Tendons. Tendons link muscle to bone. Ligaments link bones together. Cartilage is on the ends of bones (& other roles).

The equine skeletal system - bone Bone is made of 2 basic types of tissue: – Dense (compact) bone – on outside of shaft; – Spongy (cancellous) bone – on inside of shaft. The dense bone is lined by 2 membranes: – Periosteum on outer surface; – Endosteum on inner surface.

Spongy bone has “holes” filled with red bone marrow, that produces red & white blood cells & platelets. Bone gets it’s hardness from an extracellular layer of inorganic salts - calcium & phosphorus (2:1 ratio). Bone cells are well supplied with blood vessels to ensure oxygen & nutrient delivery. Bones cells are responsible for constant bone turnover, growth & repair: – Osteoblasts (bone forming); – Osteocytes (mature osteoblasts – responsible for nutrient exchange); – Osteoclasts (digest bone matrix, releasing Ca & P. Important in bone remodelling & providing a source of Ca when necessary).

Bones grow in length & girth. Maturation of bone occurs when the epiphyseal growth plates have closed. Depending on the bone, growth plates can close from 9 months – 3.5 years +. Any bone growth other than lengthening, is called modelling. Modelling = ↑ in bone mass (hypertrophy).

Properties of bone Bone is dynamic & adaptable to an extent. Some adjustments in size & shape can be made by remodelling. Rebuilding takes longer than removal → ↓ bone density. During growth, bone formation exceeds resorption → ↑ skeletal mass. Mature horses have a high rate of remodelling (bone turnover) (max. rate at 2-3 years). 50% of the skeleton is replaced by 3 yrs.

Remodelling may leave the horse weaker (↓ mineral density for several months), but is required for: – Bone repair; – Improvement / adaptation of poor original growth; – Calcium homeostasis. Bone quantity & quality is important. Bone quantity (cannon circumference) is often observed as a factor in assessing conformation. Used as an indication of weight carrying potential. Compromise: – High bone mass = slower; – Need for sufficient bone mass to avoid fractures.

Bone quality is important. Bone strength is related to bone mass, density, shape & internal composition. Bone needs some loading to maintain its mass. Bone shows elastic behaviour (returns to original shape when stress is removed) with a range of applied stresses. Bone can show inelastic behaviour (does not return to form – deformed) at certain levels of applied stress. Magnitude, rate of application of applied stress & previous level of conditioning will all determine the bone’s response. There is no easy way to measure how hard the skeleton is working.

Your turn... In pairs you will research responses to exercise. Use the internet & the book ‘Marlin & Nankervis, Equine Exercise Physiology’. Present 1 side of A4 as a handout for the rest of the class on the following: – The responses of bone to training; – The responses of cartilage to training; – Training bone in practical terms; – The responses of tendons to training.

Revision - skeleton 1.What is the function of tendons? 2.What is the function of ligaments? 3.Describe the structure of bone. 4.Name and explain the different types of bone cells. 5.What are “growth plates”? 6.What is “bone remodelling”?