Motor Control in Horses
It has become glaringly obvious to me that horses suffer many of the same, if not more pathologies than humans. Sadly. most of these dysfunctions result from our human imposed demands in these horses’ lives. With the addition of equipment such as tack and improper body care, their bodies have to withstand substantial external forces through no fault of their own mechanics or physiology.
The main area of concern I am seeing develop regularly in the body of the horse is altered motor control due to injury or imposed imbalance. This interruption in equilibrium can be caused by a multitude of factors, such as ill-fitting tack, poor hoof balance, disrupted dietary needs, lack of exercise, and the rider’s own physical limitation, to name a few. When an injury occurs, the horse must develop an altered motor pattern to still be able to move and travel.
Conversely, sometimes poor motor control, such as under conditioned core muscles, causes a weak topline, leading to an injury which may not have occurred in the first place. It’s a bit of a chicken-egg type of question but either route leads to the same ending: dysfunction and altered motor control. Whether an injury leads to an alteration of motor control or an alteration of motor control lead to an injury is still up for debate and highly case specific.
Motor control refers to “the process by which the nervous system coordinates the muscle and limbs to achieve a desired movement or set of actions; this includes the ability to anticipate, adjust and respond to deviations from the desired action” (Motor control, 2018). Since the motor system functions as a whole unit neurologically, it is distinctly neglectful to simply try to assess or rehabilitate individual segments without taking into account the function of the entire system as a whole (Cook, 2015). Movements are the result of complex multi-muscle patterning as opposed to an individual muscle contracting. Much like when you do a squat it is not just the glutes and quadriceps that are active but the entire chain of muscles from lower back to soles of feet, plus many deep core stabilizers. This is why we must look at the horse’s body as a complex system of regional interdependence which means that dysfunctions in one remote area may contribute to dysfunction at a different site. What this translates to as an equine therapist is that an owner’s report of “what the problem is” versus the true site of primary concern could be very different.
When trying to understand regional interdependence, one of the simplest ways to look at it is as the relationship between mobile and stable segments. Joints that have one primary movement plane such as a hinge joint in the knee are considered “stable” while others that don’t have a single plane of movement, such as the ball and socket hip, are considered “mobile” (Cook, 2016). The equine body (just like us humans) works in an alternating pattern of stable segments next to or on top of mobile segments. For example, the hoof is stable, while the ankle is mobile, then the knee is stable, and the shoulder is mobile and so on. The reason for this design is to give stability to heavily weighted areas while still providing ease of movement and mobility of the entire limb for complex motor patterns. It is because of this physiological makeup that we as humans and horses are able to run, cut, twist, and bolt at high speeds without injuring them/ourselves every time we do this. Dysfunction arises when previously mobile segments become stable or vice versa due to injury or imposed imbalance. For example, a knee injury will cause the shoulder and ankle to have to become stable which results in lack of fluidity in movement and altered motor control.
A horse’s issues with motor control can become hugely compounded by pain. Pain is a tricky variable in that it can alter motor control in a very unpredictable way and may also cause behaviours in the horse which would otherwise not be present. Pain can either inhibit a movement altogether (i.e. the muscles shut down) or do the exact opposite (i.e. increase muscle activation) as part of a protective guarding response. In a recent human study on biomechanical changes due to injury, data indicates that there were significant delays in motor activation and recruitment of gluteus maximus in ankle sprain patients. Even once pain free these patients still demonstrated an altered and weak motor pattern with regard to hip muscle activation (Cook, 2016). This study demonstrates that the lack of gluteal activation while the individuals were on crutches or limping led to a “permanent” inhibition of gluteal motor activation and control. Studies such as this have made me consider these factors in our equine patients. The very same can be seen in horses who have suffered severe lower limb trauma, demonstrating reduced gluteal muscle mass and difficulty engaging the hind end when asked to. Each situation is dependent on many factors and every horse will respond to pain differently based on their history, genetics, and training. Either way, it is clear that pain can also cause altered motor control and thus should be addressed first and foremost. In order to progress to more focused treatments, pain must be decreased and ideally eliminated before being able to truly target the cause of dysfunction and develop a well-rounded treatment plan. The challenge with altered motor control is that it can be difficult to assess and retrain a new recruitment pattern once the neurological system has adapted to this “old” way of moving. It takes repeated activation and conditioning of a new motor program (approximately 10,000 repetitions of a given movement pattern) to retrain the nervous system.
As I progress through my own growth as a therapist I am currently developing an assessment strategy designed to break down the movements and determine the source of dysfunction rather than chase pain. What I have found thus far is that the horse’s body acts as a true guide to where these areas lie. Muscle tension, tenderness, asymmetries, and imbalance are all palpable at relatively superficial tissue levels and visible to the trained eye during static observation as well as dynamic gait assessment. During this past year’s experience and in my studies, I have come to understand that horses are very honest with what causes them discomfort and what does not. It is the awareness and interpretation of these signals which is the true art of receiving the necessary feedback that we as therapists need in order to treat them effectively. It amazes me how willingly they communicate with us regarding their bodies and how endless the possibilities are, if all therapists could hone these “listening” skills. It is my goal to continue to grow and improve these areas so that I am better equipped to assess and correct the patterns of altered motor control, therefore reducing dysfunction and alleviating pain in the equine patient.
References
https://www.nature.com/subjects/motor-control.
Cook, G., Burton, L., Kiesel, K., Bryant, M., & Torine, J. (2015). Movement: functional movement systems: screening, assessment, and corrective strategies. Aptos, CA: On Target Publications.