Tendons are firm, usually cylindrical or flat structures that connect muscles to bones. They are made up of collagen, which has strong but elastic properties allowing shock absorption and transfer of forces. Under load, tendons undergo a stretch shortening cycle, where they lengthen, building and storing energy which is released as physical energy when the tendon shortens again. Think of a slinky, which uses repeatable stretch shortening cycles to create movement. Or a kangaroo, hopping around. Tendons act in similar ways in horses, providing economy for gait and force generation of the limbs, which are controlled by muscles closer to the center of their body. 

Gait analysis and electromyographic studies have shown that a horse's use of tendons in this way actually reduces the energy required by the horse by up to 36% during gait (O’Brien, Marr and Thorpe, 2020; Verkade, Back and Birch, 2019). 

These studies have also shown us activities and phases of gait that experience the highest loads, such as landing from a jump, and on mid stance during gallop (O’Brien, Niel and Marr, 2020). Another factor that increases tendon load is duty factor (the amount of time in contact with the ground), which is increased in high level dressage movements such as passage (Murray et al., 2006). Other factors that increase tendon loading include increase in gait speed, and more compliant, softer surfaces such as sand (Crevior-Denoix et al., 2013). 

Tendon injury occurs when there is repeated and extensive stretching of tendons during training. This overwhelms the capacity of tendon cells to repair before the subsequent loading cycle, leading to disruption to the collagen organization, which reduces the tensile strength of the tendon and makes it more susceptible to future overload (Bohm, Mersmann and Arampatzis, 2015). Disrepair and micro tearing within the tendon then generates a pain response, causing dysfunction and poor performance. 

Human and equine tendons are comprised of identical structural and cellular make up, allowing the transference of decades of tendon management knowledge from humans, to the equine animal. In order to improve function, the first and foremost thing to address is pain. To do this, physiotherapists around the world use slow, heavy isometric (Static) exercise to provide pain relief and pain free stimulation to tendon structures, and this concept can be applied exactly the same in horses (Bohm, Mersmann and Arampatzis, 2015). 

Once pain is controlled and the tendon has been de-loaded adequately, it is time to begin a progressive and graded strengthening and load management program. Qualified physiotherapists are able to evaluate the amount of load that is enough to generate cellular adaptation while avoiding overload and microdamage. Doing this stimulates collagen growth and organization in the tendon, laying down structure once again to allow its function of shock absorption and storage of energy (Heinemeier and Kjaer, 2011. 

If your horse has a tendon injury, your physiotherapy will work together with you over a period of months (Tendons have longer remodeling time frames than other tissues) to ensure the correct and appropriate load for the stage of recovery (Bohm, Mersmann and Arampatzis, 2015). References 

Bohm, S., Mersmann, F., & Arampatzis, A. (2015). “Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis of exercise intervention studies on healthy adults”. Sports medicine - open, 1(1), pp. 7. 

Brumitt, J., & Cuddeford, T. (2015). “Current Concepts of Muscle and Tendon Adapation to Strength and Conditioning”. International journal of sports physical therapy, 10(6), pp. 748– 759.

Crevier-Denoix, N. et al. (2013) “Comparison of superficial digital flexor tendon loading on asphalt and sand in horses at the walk and trot”. The Veterinary Journal, 198. 

Firth, E. (2006) “The response of bone, articular cartilage and tendon to exercise in the horse”. Journal of Anatomy, 208(4), pp.513-526. 

Heinemeier, K. and Kjaer, M. (2011) “In vivo investigation of tendon responses to mechanical loading', Journal Of Musculoskeletal & Neuronal Interactions, 11(2), pp. 115-123.

Lichtwark, G., Watson, J., Mavrommatis, S. and Wilson, A. (2009) “Intensity of activation and timing of deactivation modulate elastic energy storage and release in a pennate muscle and account for gait-specific initiation of limb protraction in the horse.” Journal of Experimental Biology, 212(15) pp.2454-2463. 

O’Brien, C, Marr, N, Thorpe, C. (2021) “Microdamage in the equine superficial digital flexor tendon.” Equine Vet Journal, pp. 53: 417– 430. 

R.C. Murray, S.J. Dyson, C. Tranquille, V. Adams (2006) “Association of type of sport and performance level with anatomical site of orthopaedic injury diagnosis - Equine Exercise Physiology.” Equine Veterinary Journal, pp. 411-416. 

Verkade, M., Back, W. and Birch, H. (2019) “Equine digital tendons show breed-specific differences in their mechanical properties that may relate to athletic ability and predisposition to Injury.” Equine Veterinary Journal, 52(2), pp.320-325. 

Wilson, A., Watson, J. and Lichtwark, G. (2003) “A catapult action for rapid limb protraction.” Nature, 421(6918), pp.35-36.