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Musculoskeletal: effects of training and exercise



  • Skeletal muscle can adapt in response to use (exercise) throughout life.
  • Muscle tissue can provide an energy reserve in the form of amino acids during prolonged malnutrition → atrophy (reversible).
  • Skeletal muscle consists of fibers varying in their metabolism, ie oxidative capacity, and contractility.
  • Distribution of fibers depends on genetic factors and type of training, eg Quarterhorses Quarterhorse (different from Arabians Arab).
  • Aerobic exercise (endurance training) → transition of muscle fiber type to those that use oxygen → lean appearance of the horse.
  • Anaerobic exercise (resistant/sprint training) → transition of muscle fiber types that work without the use of oxygen → bulkier musculature.
Print off the Owner factsheet Exercise - keeping your horse fit and happy to give to your clients.

Fiber types

Type I fibers
  • Low myosin-ATPase activity = slow contracting or slow twitch.
  • Fatigue resistant (slower relaxation time).
  • Low glycolytic activity.
  • Small diameter.
  • Innervated by low threshold, small diameter motor neurones.
  • Used in maintenance of posture and movement at low speeds.
Type II fibers
  • High myosin-ATPase activity = fast contracting or fast twitch.
  • High glycolytic activity.
  • Divided into Type IIA, IIB and IIC subtypes.
  • Generally larger diameter.
  • Innervated by large diameter higher threshold motor neurones.
  • Type IIA fibers used with increase in speed.
  • Type IIB used for forceful contractions, eg acceleration and jumping, and to maintain high speeds.


  • Improves oxidative capacity.
  • Increases aerobic capacity.
  • Increases the proportion of fast-twitch fatigue-resistant fibers.  

Threshold of intensity >80% VO2 max is necessary to bring about switch in fiber type.

  • Influence of training will depend on type/intensity of training.
  • Blood lactate accumulation occurs at higher speeds.
  • At submaximal intensity, eg endurance and some pacing/trotting competitions, there is increased utilization of free fatty acids (= glycogen-sparing effect) → improved endurance capacity.
  • Metabolic changes that result from training are sustained for several weeks during detraining. Reduce training intensity once optimal fitness is obtained during competition seasons.


  • Fatigue is a result of impaired muscle fiber function.
  • Fatigue is gradual - an entire group of fibers does not fatigue simultaneously.
  • Possible causes of impaired fiber function:
    • Loss of energy substrate.
    • Altered ATP function.
    • Altered electrolyte gradients → neuromuscular unit alterations.
    • Dysfunctional calcium uptake and release by sarcoplasmic reticulum → altered contractility.
    • Altered blood flow.
    • Increased muscle temperature.
  • High intensity exercise is associated with:
    • Anaerobic metabolism.
    • Lactate accumulation.
    • Loss of muscle ATP.
    • Intramuscular potassium depletion.
    • Glycogen depletion.
    • Changes in free fatty acids and amino acids.
    • Muscle temperature.
  • Low intensity exercise is associated with:
    • Free fatty acid and glycogen as prime energy source.
    • Glycogen depletion and increase in circulating free fatty acids.
    • Recruitment of all muscle fiber types.
    • Utilization of intramuscular glycogen.
  • Fatigued muscles are unable to provide enough support to associated structures, eg joints, therefore in an exhausted horse there is less protection, poor stability, and increased risk of injury of muscles of other tissues/structures.
  • Exercising at a higher intensity or for a longer duration than is appropriate for the level of fitness or training can increase the risk of injury to muscle and associated structures such as tendon, joints and ligaments.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Firth E C (2006) The response of bone, articular cartilage and tendon to exercise in the horse. J Anatomy 208 (4), 513-526 PubMed.
  • Murray J K, Singer E R, Saxby F & French N P (2004) Factors influencing risk of injury to horses falling during eventing. Vet Rec 154 (7), 207-208 PubMed.
  • Graham-Thiers P M, Krongeld D S et al (2004) Dietary protein and fat effects on protein status in Arabian horses during interval training and repeated sprints. J Equine Vet Sci 23 (12), 554-559 VetMedResource.
  • Stephen J O et al (2003) Risk factors and prevalence of injuries in horses during various types of steeplechase races. JAVMA 233 (12), 1788-1790 PubMed.
  • Murray R C, Vedi S, Birch H L, Lakhani K H & Goodship A E (2001) Subchondral bone thickness, hardness and remodelling are influenced by short-term exercise in a site-specific manner. J Ortho Res 19 (6), 1035-1042 PubMed.
  • Cornelissen B P M, van Weeren P A, Ederveen A G H & Barneeveld A (1999) Influence of exercise on bone mineral density of immature cortical and trabecular bone of the equine metacarpus and proximal sesamoid bone. Equine Vet J Suppl 31, 79-85 PubMed.
  • van Weeren P R & Barneveld A (1999) Study design to evaluate the influence of exercise on the development of the musculoskeletal system of foals up to age 11 months. Equine Vet J Suppl 31, 4-8 PubMed.
  • McCarthy R N & Jeffcott L B (1992) Effects of treadmill exercise on cortical bone in the third metacarpus of young horses. Res Vet Sci 52, 28-37 PubMed.

Other sources of information

  • Nunamaker D M (1996) Metacarpal Stress Fractures. In: Equine Fracture Repair. Ed: A J Nixon. W B Saunders, USA. ISBN: 0-7216-6754-6.
  • Dalin G & Jeffcott L B (1994) Biomechanics, Gait and Conformation. In: The Athletic Horse - Principles and Practice of Equine Sports Medicine. Eds: R J Rose & D R Hodgson. W B Saunders, USA. ISBN: 0-7216-3759-0.
  • Snow D H & Valberg S J (1994) Muscle Anatomy, Physiology and Adaptations to Exercise and Training. In: The Athletic Horse - Principles and Practice of Equine Sports Medicine. Eds: R J Rose & D R Hodgson. W B Saunders, USA. ISBN: 0-7216-3759-0.
  • Bramlage L R, Bukowiecki C W & Gabel A A (1989) The Effect of Training on the Suspensory Apparatus of the Horse. In: Proc AAEP 35. pp 245-247.

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