- Review two types of chronic ankle instability, including mechanical and functional.
- Review the different types of neuromuscular control, including open-loop and closed-loop systems.
- Introduce training techniques that can better optimize the neuromuscular system to improve ankle stability and reduce the risk of recurrent ankle sprains.
Ankle sprains are one of the most common injuries in physically active individuals – and one of the most common foot and ankle related injuries treated in an emergency room setting. It is estimated that up to 70% of individuals who experience an ankle sprain have residual symptoms including instability or recurrent sprains (Hoch, 2012). This persistent instability is referred to as chronic ankle instability (CAI).
To date, most research has focused on the residual impairment within the proprioceptors of the musculotendinous junction, the connection between a muscle and its tendon, and joint capsule, the dense connective tissue forming a sleeve around the joint. In response to this research, most CAI treatment programs include your standard “proprioceptive," or balance exercises, and peroneal muscle strengthening.
With the prevalence of CAI and advances in exercise science, it is important to periodically review a client’s program design to determine if the most current treatment guidelines are implemented in the training program and if the exercise selection follows evidence-based practice.
This article will review the latest research in proprioceptive training and neuromuscular control of the ankle. This article will also challenge current rehabilitation programs and apply evidence-based practice toward a new way of looking at “proprioceptive training” as applied to CAI.
Types of Ankle Instability
When approaching a client or athlete with chronic ankle instability, it is important to understand the two types of ankle instability – mechanical and functional.
The first, mechanical ankle instability (MAI), is an actual structural reason for ankle laxity. The lateral ankle ligaments play a key role in the structural support of the ankle joint. Limiting plantarflexion and inversion, the anterior tibial fibular ligament (ATFL) is the most common injured ligament during an ankle sprain. This lateral ligament is typically injured while the ankle experiences an inversion ankle sprain, or an outward rolling of the ankle. Depending on the severity of the ankle sprain, a partial or complete tear of this ligament will greatly compromise the stability of the ankle. These patients often go on to have surgical correction.
The second type of chronic ankle instability is when the individual experiences symptoms of ankle “weakness” or that the ankle is “giving way." Referred to as functional ankle instability (FAI), mechanical laxity has been ruled out in these individuals and therefore an impairment in neuromuscular control must be considered.
As fitness professionals, the most common type of chronic ankle instability you will encounter is functional ankle instability (FAI), therefore this will be the focus of this article.
Neuromuscular Control of the Ankle and FAI
Defined as the interaction between the nervous system and the muscular skeletal system to produce a desired effect, neuromuscular control is the cornerstone to all human movement (Ogard, 2011). There are two subdivisions within neuromuscular control, the open-loop system and the closed-loop system. Just like closed-chain and open-chain kinematics, we must consider both subdivisions when we train the neuromuscular system.
Open-loop neuromuscular control is often referred to as the preparatory phase of human movement. More specifically, this is the pre-activation of the ankle stabilizers before the foot even touches the ground. This is a protective mechanism that allows the body to better react to ground reaction forces and unstable surfaces. Studies have shown that individuals with FAI have a lower pre-activation state of their ankle stabilizers, namely the peroneals, and therefore strike the ground with more instability and in a more inverted position (Ogard, 2011).
Closed-loop neuromuscular control is a reactive or reflexive-type muscle contraction in response to afferent sensory input, input that is received by the muscles and transmitted to the brain. A great example of closed-loop neuromuscular control is when you accidentally step off of the side of a curb. Peroneal muscle spindles sense the inversion stretch (afferent signal) which creates a reflex-type concentric contraction of the peroneals to quickly pull your foot into eversion (efferent signal). This efferent signal is the brain, or central nervous system, responding to the afferent signal received and sending input to the muscles to react.
With the peroneal muscles coined as the “primary lateral ankle stabilizers," strengthening the peroneal muscles is the foundation to closed-loop neuromuscular training and most ankle rehabilitation programs.
“Proprioceptive Theory” for Ankle Instability
When a patient is referred to physical therapy for an acute sprain or CAI, the foundation of the treatment program is most often “proprioceptive” exercises. Often times, the referring physician will write on the prescription “proprioceptive training."
For the past two decades, ankle rehab programs have been following the “Proprioceptive Theory” for ankle instability. The “Proprioceptive Theory” for ankle instability states that joint and peroneal tendon proprioceptors are disrupted during rapid ankle inversion, and therefore must be strengthened to regain ankle stability.
But what exactly constitutes “proprioceptive training”?
Current Concepts in Proprioceptive Training
A 2011 study by Ogard et al. argues that although ”proprioceptive training” is a key component to ankle rehabilitation programs, it does not clearly define proprioceptive training.
“Proprioceptive training” is often synonymous with balance training. By definition, “balance” is our body’s ability to maintain center of mass within our base of support (Ogard, 2011). However, “proprioception” is the central nervous system processing limb and trunk movements while balancing.
There are several balance exercises that are included in rehab or personal training programs with the intention of improving a client’s proprioceptive abilities. However, these exercises may not be as effective as expected. For example, a common exercise that is considered to be a “proprioceptive” exercise – standing on an Airex pad – may not yield the necessary proprioceptive training needed to restore ankle stability. While standing on this unstable surface, the proprioceptive feedback from our feet and ankles is dampened and shifted which means our somatosensory system increases the sensory input from both the visual and vestibular systems. In other words, this exercise may not be really training our “proprioceptors,” but rather re-allocating sensory input to maintain balance.
So if these unstable surfaces, which are the hallmark to ankle rehab programs everywhere, are not stimulating our proprioceptors – are they even improving our stability?
A 2007 study by Refshauge et al. evaluated the impact of ankle proprioception and stability after 4 weeks of wobble board training in subjects with FAI. What was observed is that wobble board training only improved movement detection velocity at the slowest speed. Studies have suggested that ankle inversion velocities are up to 3.5 degrees per second, however the wobble board program was associated with only a 1.1 degree per second.
Although the current ankle rehab programs focus on improving balance and proprioception through unstable surfaces, the research does not support this with an associated reduction in ankle instability. If this is the case, how can we better create rehabilitation programs that better stimulate the proprioceptive system and therefore better reduce risk of injury or re-injury?
Rethinking Proprioceptive Training
With the popularity of minimalist footwear and barefoot running, some of the same concepts are taken into ankle rehabilitation programs. One of the greatest benefits to barefoot or minimalist running is the degree of proprioceptive input with each step they take.
One of the most important sensory input systems in the human body is skin on the bottom of the foot. Thousands of mechanoreceptors that are sensitive to light touch, texture, vibration, pressure and skin stretch are stimulated with every shift of the body and each step we take. As these different mechanoreceptors are stimulated, specific muscle activation patterns are stimulated to stabilize the foot and ankle joints, as well as to dissipate ground reaction forces.
Recommended Proprioceptive Training
It is better to stimulate the mechanoreceptors in the plantar foot which are faster than ligament and musculotendon proprioceptors. The following are training techniques that can better optimize the neuromuscular system in order to improve ankle stability and reduce the risk of recurrent ankle sprains.
Note: The following information does not qualify a fitness professional to perform these techniques with their clients. If necessary, it is recommended that the fitness professional seek the proper training and/or certifications in order to incorporate these techniques into a client's routine.
Based off of feedback from Merkel’s Disks, texture offers a great way to stimulate the most sensitive of the plantar cutaneous receptors. Studies have shown that when comparing stabilization when standing on textured surfaces versus smooth surfaces, there was a greater than 9% decrease in postural sway with the textured surfaces (Hatton 2011). A great way to begin introducing different textures in your client’s programming is by standing on the underside of a DynaDisc.
The ridges on the underside of a DynaDisc are designed to stimulate the many proprioceptors on the bottom of the foot. Depending on the level of your client, begin with minimal or no air within the DynaDisc, then add air as they become stronger.
With your client barefoot, have them begin by standing with both feet on the DynaDisc. Eventually, integrate 20 – 30 second periods with the eyes closed to further recruit feedback from the plantar foot. As the client becomes stronger, the client can progress to a single leg stance with eyes open and single leg stance with eyes closed.
Another great technique for stimulating the plantar cutaneous receptors is specific to vibration response. Again, this proprioceptive feedback is most acute when the client is barefoot. Some fitness professionals have access to whole body vibration surfaces such as a PowerPlate. Whole body vibration platforms offer a great surface for performing all balance or single leg exercises. Depending on the type of vibration surface, both static and dynamic balance exercises can be integrated.
3. Ankle taping:
One of my preferred techniques for enhancing proprioceptive feedback is through the stimulation of skin stretch. Studies have demonstrated increased reaction time and joint position sense in athletes who have their ankle taped. It was found that this faster response time was directly related to the stimulation of Ruffini organs which are sensitive to skin stretch.
You can easily integrate skin stretch proprioceptive feedback into your client’s programming by placing tape from the lateral to medial ankle and from distal to proximal on the plantar aspect of the foot. Note: Taping clients may not be in the scope of practice for all fitness professionals. It is highly recommended to seek professional guidance, and/or proper training prior to implementing taping into a client's routine.
One of the most common forms of ankle instability witnessed by fitness professionals in their clients is functional ankle instability (FAI), described as ankle weakness or "giving way." As a result of this instability, the client may be directed to engage in physical therapy and/or personal training involving "proprioceptive training," commonly interpreted as balance training. Although the traditional balance exercises utilized in many ankle rehabilitation programs have the intention of improving a client's stability, these exercises may not be as effective as expected. Simply, balance exercises may not be enough to stimulate the proprioceptors needed to optimize the neuromuscular system in order to improve ankle stability. By stimulating the mechanoreceptors in the plantar foot with training techniques involving equipment with textures, vibration, or skin stretch, there may be a greater improvement in ankle stability and reduced risk of recurrent ankle sprain
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- Hatton, AL et al. Standing on textured surfaces effects standing balance in healthy older adults. Age Ageing, 2011. 40(3): 363 – 368.
- Hoch, M. et al. Plantar vibrotactile detection deficits in adults with chronic ankle instability. Med & Science in Sports & Exercise, 2012. 44(4): 666-672.
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