Muscular asymmetry in equine athletes is not an uncommon condition, however it usually remains undetected until it becomes clearly visible. One of the reasons why muscle asymmetry occurs is a compensation for pain and tension, that usually arises from an injury or strain or as the result of overloading of structures such as ligaments and tendons in the distal limb. Horses redistribute their weight over their body and find a new, comfortable pattern of movement that over time can result in muscular imbalance. If this condition remains unchecked it can lead to a progression of compensation, and in that way an increased risk of repetitive injury and loss of performance – sometimes with this vicious circle never being resolved. Therefore, it is very important to avoid the progression of muscular asymmetry and thereby minimize the risk of a compensatory injury with the possibility of resulting lameness.
A recent study by the biomechanics research team at the University of Copenhagen (Jensen A.M., Ahmed W., Elbrønd V., Harrison A.) published in the Journal of Equine Veterinary Sciences (2018, Vol. 68, pp. 73-80) took a closer look at the diagnosis and treatment of muscular asymmetry.
The scientists measured eight healthy, non-lame horses using an Acoustic Myography (AMG) system, which is a noninvasive and pain free method for muscle function assessment. It is based on the recording of sounds produced by contracting muscles. The device (CURO; MyoDynamik ApS) is easy to apply to the horse and capable of monitoring muscle activity as horses exercise. The muscle measured in this study was the superficial gluteal muscle, responsible for hip flexion, protraction and abduction of the hind limb. All horses were tested in walk, trot and canter on both left and right-hand circles. The most significant muscular imbalance was revealed by the horses on the left hand circle, whereas on the right hand circle the imbalance was minimal (statistically insignificant). Based on this finding, a rehabilitation program was set up – namely a 1 hour proprioceptive training regimen with use of a loose bell boot on the weaker leg, every 3 days for a period of 6 weeks. Proprioception is the sense of the relative position of one’s own body parts and the strength of effort being employed in movement. The main purpose of the proprioceptive training was to activate subcutaneous mechanoreceptors and thereby strengthen the body’s own awareness at the level of neurological pathways.
The application of such simple, light proprioceptive stimuli appeared to be enough to correct the measured muscular imbalance, as all of the horses measured again at the end of the study (week 6) showed no significant signs of muscular asymmetry using the AMG system. The authors concluded that a slight musculoskeletal imbalance, which is believed through altered stress to induce tissue strain and over time subsequent injury leading to lameness, can not only be accurately detected using the AMG system, but can also be corrected through a program of proprioceptive training.
Jensen Anne-Mette, Ahmed Waqas, Elbrønd Vibeke, Harrison Adrian P.: The Efficacy of Intermittent Long-term Bell Boot Application for the Correction of Muscle Asymmetry in Equine Subjects. Journal of Equine Veterinary Science, 68 (2018), pp.73-80.
More information about Acoustic Myography and CURO system available here: www.myodynamik.com