Ankle Stability and Intrinsic Foot Muscles: A Natural Approach to Injury Prevention

Have you ever stopped to think about ankle support? Why do most studies focus on the effects of external support on prevention while totally ignoring the function of muscular support originating from the intrinsic foot muscles? It seems all studies are aiming to solve a very specific problem: how to brace the ankle in order to arrest the motion of a lateral ankle sprain in an unstable lower kinetic chain system. Researchers were missing the problem right in front of them—why was the system unstable in the first place? In the past decade, researchers have started to investigate the relationship between intrinsic foot muscles, extrinsic leg muscles, and how to stabilize the ankle from within, rather than from the outside.

Ankle Sprains in Youth Athletes: A Common and Recurrent Problem

Ankle sprains are the most prevalent injury among young athletes, especially among court athletes and young girls.¹ Children under 17 are the most susceptible to ankle sprains.² Ankle sprains account for around 7% of all injuries sustained during college athletics.³ Once an ankle sprain occurs, around 40% of patients go on to experience chronic ankle instability, making them much more susceptible to reinjury.^{4, 5} Female athletes are particularly prone to experiencing recurrent injuries in basketball, track, and field hockey, with more than 20% of lateral ankle sprains being recurrent injuries.³

Predictors of Ankle Sprains in Athletes

What are the predictive risk factors for an ankle sprain? Female sex,^{1, 2, 6, 7} hip abductor and extensor weakness,^{1, 8, 9} poor performance on balance and hopping tests,^{1, 10, 11, 12, 13, 14, 15, 16, 17, 18} and taking part in court sports^{1, 2} are all risk factors for an acute lateral ankle sprain. Interestingly, field playing surfaces (artificial turf vs. natural grass) were not found to be predictors of ankle sprains, with injury rates being nearly the same.^{19, 20}

While no studies have explored the protective factor of intrinsic foot muscle strength for preventing a first ankle sprain, studies have examined the relationship between post-injury instability and intrinsic foot muscle atrophy.^{21, 22} It was found that subjects with chronic ankle instability had less muscular volume and activation of their foot muscles.^{21, 22} Furthermore, studies involving foot muscle strengthening in chronic ankle instability patients have demonstrated that restoring strength and function to the foot muscles significantly improves postural stability and balance control, both of which are major predictors of ankle sprain prevention.²³

Two meta-analyses on intrinsic foot muscle training have shown improved balance from various training protocols, including short foot and toe-spread exercises.^{24, 25} Poor performance on balance and hopping tests is strongly correlated with a higher risk of ankle sprains.^{1, 10, 11, 12, 13, 14, 15, 16, 17, 18} Therefore, it can be concluded that children raised barefoot or in minimalist shoes, who demonstrate superior balance and jumping abilities,^{26, 27} may experience a lesser incidence of ankle sprains compared to children wearing supportive, cushioned, and deforming shoes. More peer-reviewed studies are needed to fully explore the preventative impact of foot strengthening on the first incidence of a lateral ankle sprain, but it has been shown that foot strengthening improves strength and coordination, directly impacting the prevalence of recurrent ankle sprains.^{24, 25, 28, 29}

External Support and its Impact on Ankle Stability

Let us consider the effectiveness of external support on the muscles that directly stabilize the ankles. According to various studies, applying external support to the ankle in the form of a brace leads to less muscle activity and slower muscle reaction times of the muscles that control ankle stability, such as the peroneus longus, gastrocnemius, soleus, and the gluteus medius.^{30, 31, 32}

The wear of supportive high-top shoes delays the muscle reaction times of the ankle evertor muscles, which are needed to counteract a lateral ankle sprain.³³ Additionally, applying orthotic support to the arch of the foot decreases the muscular activity of the gluteus muscles (maximus and medius)³⁴ and atrophies the intrinsic muscles of the foot, which are directly involved in balance.³⁵

Finally, applying ankle braces to otherwise healthy athletes led to decreased dynamic balance ability after a full 12-week volleyball season.³⁶ As mentioned previously, lack of balance,^{1, 10, 11, 12, 13, 14, 15, 16, 17, 18} lack of hip abductor strength,⁹ and lack of hip extensor strength⁸ are predictive factors for an increased risk of a lateral ankle sprain. Bracing the ankle and foot makes athletes more prone to ankle sprains by robbing them of the ability to build strength and use the foot-ankle complex’s natural strength. Worse, ankle bracing increases the risk of knee sprains and tears by increasing knee internal rotation and knee abduction.^{37, 38, 39}

Preventing Ankle Sprains through Natural Foot Development

How would an athlete perform if they were able to build the strength and coordination needed to prevent ankle sprains through natural foot development? Children raised in natural athletic movement while barefoot have notably better coordination and balance than children who spend most of their time in supportive and constrictive footwear.^{26, 27} The benefits extend beyond children raised barefoot; those in minimalist shoes perform better in balance and jumping than children in supportive and constrictive footwear.⁴⁰

It has been found that transitioning to minimalist shoes over 8 weeks can strengthen foot muscles nearly as well as an 8-week foot strengthening exercise program.⁴¹ Furthermore, strengthening the glute muscles alongside the foot muscles yields a greater benefit to balance than foot strengthening alone.^{42, 43, 44} Running barefoot or in minimalist shoes has been shown to increase glute muscle activity more than running in supportive footwear.^{45, 46}

Combining the benefits of glute and foot strengthening while wearing minimalist shoes,^{41, 45, 46} along with the fact that children perform better at balancing, sprinting, and jumping while barefoot or in minimalist shoes,^{26, 27, 40} it is clear that competing in minimalist shoes will help prevent ankle sprains. The risk factors for ankle sprains—lack of balance,^{1, 10, 11, 12, 13, 14, 15, 16, 17, 18} lack of hip abductor strength,⁹ and lack of hip extensor strength⁸ all point to the need for natural foot development through minimalist footwear.