What Your PT Wants You To Know About Ankle Injury Prevention

Ankle injuries can be debilitating to the hard working athlete and can cause precious time to be lost from sport. To make matters worse, once the ankle is injured, it is more likely to be injured again.

But the good news: these injuries, and recurring injuries, can be prevented. The athlete can decrease their risk of injury with commitment to rehabilitation, education on the types of ankle injuries, education on how these injuries happen, and possibly the right brace or shoe. In this article we will dive into all of these categories in detail.

First, we talk in detail about the anatomical structures involved and the types of ankle injures. To truly understand a problem, knowledge is needed about both the components and the cause. Knowing these parts will lead to a quicker solution.

Next, we cover some steps to take if you have already been injured. The take away: it’s never a bad idea to get some advice from a medical professional.

Finally, we get to the good part: exercises, training tips, equipment, braces, taping and shoes. Here we go!

A Quick Review of the Ankle’s Anatomy

To understand why and how ankles are injured, it’s important to have a brief understanding of the bones, muscles, ligaments and movements of the ankle. 

Lets Start With the Basic Movements

You can move your own ankle to gain a better understanding. 

Point your toe like a ballerina, this is called plantarflexion. 

“Flex” your foot by bringing your toes towards your face. This is called dorsiflexion. 

Pretend there is a light shining from the bottom of your foot, and shine the light towards your opposite foot. This is called inversion. 

Shine the light towards the outside of your body. This is called eversion. 

Joint Structure of the Ankle 

The ankle joint is actually composed of three (yes, three!) different joints:the Inferior Tibiofibular Joint, the Talocrural Joint, and the Subtalar Joint. 

The tibia and fibula are the two bones of the lower leg which run parallel to each other, and at the bottom they touch to form the inferior tibiofibular joint. When these two bones join, they form a concave arch of bone, sometimes referred to as the ankle “mortise” as pictured below. 

The talocrural joint is composed of the tibia and fibula on top of the talus bone. The talus forms a convex dome shape where it fits underneath the arch (mortise) made by the tibia and fibula.

In the picture below, the labeled “ankle joint” is the Talocrural Joint.

The last joint of the ankle is the subtalar joint, which is where the talus meets the bone underneath it, the calcaneus (what we typically think of as our “heel”). 

Muscles 

There are 10 different muscles that cross the ankle joints. Although they are all important for stabilization and movement of the ankle in complex ways, a complete review of them would be out of the scope of this article. However, here is a list of their basic actions: 

• Tibialis Anterior – dorsiflexion, inversion 
• Tibialis Posterior – inversion, plantarflexion 
• Gastrocnemius – plantarflexion
• Soleus – plantarflexion 
• Fibularis Longus, Brevis, and Tertius – a group of muscles that performs primarily eversion 
• Extensor Digitorum Longus – extends the toes, dorsiflexion
• Flexor Digitorum Longus – flexes the toes, plantarflexion 
• Flexor Hallucis Longus – flexes big toe, minimally supinates and plantarflexes ankle 

Here are some resources if you would like to further your knowledge: 

Muscles Resource 1

Muscles Resource 2

Ligaments 

A ligament is simply a band of fibrous tissue which connects bone to other bones, usually for stability and support. There are many ligaments associated with the joints of the ankle that are also important for stabilization. Ligaments at risk of damage will be discussed within individual injuries. 

If you would like to further your knowledge, here are some resources: 

Ankle Ligament Resource 1

Ankle Ligament Resource 2

Types of Ankle Injuries 

According to a study by Verhagen et al., the typical volleyball ankle injury results in an average of 4.5 weeks lost from competition. To prevent these kinds of debilitating injuries and time lost from sport, we must first understand what they are, how they happen, and what kind of structures are involved.

Typically, the word injury has the connotation of a traumatic, brief event that can have lasting effects. This would be what is referred to as an “acute” injury. There are also “chronic” injuries, which usually result from overuse over time. 

We will cover a couple of acute and chronic injuries. Although not an all inclusive list, we will focus on the most common ankle injuries in sport. 

The Inversion Sprain 

The most prevalent ankle injury in volleyball is an inversion sprain. This often occurs when a player lands on another player’s foot after blocking their opponent at the center line (Reeser, et al., 2006). The bottom of the foot rolls inwards, placing extreme strain on the muscles and ligaments found on the outside of the ankle. 

You’ve likely experienced this same pain if you have “twisted your ankle” from your foot slipping off a curb. The pain is usually intense at first and then subsides after a couple of minutes. However, in sport this can affect performance as the athlete is hesitant to bear weight through that foot and even minor damage will increase chances of future injury. 

This type of injury is often acute, with damage occurring with a single event. However, this can also be a recurring injury. Ligaments and structures become weakened over time with smaller, less severe events. Up to 80% of ankle sprains occur after previous injury, making proper rehabilitation after injury crucial to future health of the ankle (Bahr et al., 1997)

With inversion ankle sprains, the ligaments on the outside of the ankle can tear partially or completely. These important ligaments include the anterior talofibular ligament (ATFL), posterior talofibular ligament (PTFL), and the calcaneofibular ligament (CFL). Without full integrity of these ligaments, the ankle joint becomes less stable and will rely more on the surrounding muscles to keep it in alignment, possibly causing further strain. 

In addition to ligament damage, muscles that cross the outside of the ankle can be damaged as well. When the muscle is stretched or partially torn, we call this a muscle strain. The muscles most likely to be affected are the Fibularis Longus and Brevis.

Symptoms of Inversion Ankle Sprain

Other symptoms of ankle sprain can include swelling, inability to bear weight on foot, a catching or popping sensation, bruising, pain to touch, and feeling on instability at the ankle.

Treatment of Inversion Ankle Sprains

Treatment is usually conservative, consisting of the RICE principle: Rest, Ice, Compression, and Elevation. Certain ankle braces, taping techniques, and modification to landing techniques can also be used after injury. In extreme situations, bone fracture or complete tear of ligaments can occur, requiring more involved treatment.

The High Ankle Sprain

Another type of sprain that can be seen in athletes is the high ankle sprain. This has a different method of injury and different ligaments injured than in an inversion ankle sprain.

This occurs when the bottom of the foot is turned outwards (eversion), as opposed to being turned inwards with an inversion ankle sprain. This can occur with poor landing techniques, or potentially a blow to the outside of the ankle from another player.

The ligaments affected are those that hold the tibia and fibula together. When the foot is suddenly everted, the talus is jammed upwards and produces force that attempts to separate the tibia and fibula.

This causes extreme strain to the following ligaments that hold them together: anterior-inferior tibiofibular ligament (AITFL), posterior-inferior tibiofibular ligament (PITFL), Interosseus membrane, Interosseus ligament (IOL), and the inferior transverse ligament (ITL), (Molinari et al., 2009).

In addition, ligaments on the inside of the ankle can be damaged as well, and these are known as the Deltoid Ligaments.

Treatment and Recovery Times for High Ankle Sprain

Although less prevalent in volleyball players, the high ankle sprain can be more severe and more variable with recovery, with averages up to 52 days lost from sport (Molianary et al., 2009). Treatment can range from a non-weight bearing boot in more mild cases, to surgery in more severe cases.

A Quick Overview on Ankle Sprain Grading

Ankle sprains are categorized into “grades”, based on their severity and symptoms. The categories are Grade I, Grade II and Grade III. Grade I is the least severe and Grade III is the most severe.

Your orthopedic physician will decide the severity based on special tests of ligament integrity, amount of swelling and bruising, and ability or inability to walk on the affected foot.

Overuse Injuries

These injuries get their own category since they all have one factor in common: over use. Intense practice schedules combined with lack of cross-training and no rest days can take a toll on a young person’s body, no matter how “strong” they may seem. The following are possible consequences.

Stress Fractures

Mayer et al. defines a stress fracture: “In contrast to acute fractures, which typically occur with a single maximal load, stress fractures occur due to repetitive, submaximal loading of a bone, leading to microfractures that are unable to heal due to bone resorption and bone formation imbalances.”

Simply put, repetitive stress over time can cause tiny breaks in the bone that do not heal. Stress fractures can affect all of the bones of the ankle and foot.

The repetitive stress that would cause this in volleyball is jumping and landing. That is why proper landing techniques are so important for preventing pain and injury. Read on to the exercise section below for helpful tips.

Stress Fractures in Female Athletes

Female athletes are more likely to have a stress fracture than males for many reasons, including a wider pelvis which affects force through the lower body, less muscle mass to protect bones from acute forces, and presence of the female athlete triad (Mayer et al., 2014).

Some of these factors are not able to be changed, such as bone structure and differences in physiology between the sexes. However, important factors such as nutrition and proper rest will be vital to decreasing stress fractures in our female athletes.

Symptoms of Stress Fractures

The most common symptoms of a stress fracture are inability to bear weight through the affected leg, and tenderness to the bone with palpation (aka, pressing on it).

Diagnosing Stress Fractures

Stress fractures can be difficult to diagnose, as x-rays will often not show any evidence for the first two weeks, and sometimes longer. This has to do with the bone’s slow healing process. Other imaging studies such as MRI or CT scans can be more helpful when the diagnosis is not clear. Your physician will make these judgments.

Treatment of Stress Fractures

Treatment for stress fractures will range depending on severity of fracture and which bone is fractured. This may include non-weight bearing for a certain amount of time, rest from sport, and physical therapy to maintain integrity of surrounding muscles and bones (Astur et al,. 2015). Certain fractures may require surgery for proper healing. Regardless, you can expect a healing time of at least 2-3 months.

Plantar Fasciitis

It sounds complicated, but let’s break it down:

Plantar: this means the bottom of your foot

Fasciitis: fascia (thick connective tissue) + itis (inflammation)

So, this tissue (fascia) on the bottom of your foot is inflamed.

This causes pain to the bottom of the foot that can occur at any age and at any level of sport. Typically, the pain will be the most intense closest to the heel. This is where the connective tissue (plantar fascia) begins, and will extend to the toes.

The plantar fascia helps to absorb forces through the foot, and create tension when pushing off with the foot during walking, running, or jumping. All of these activities will be difficult when the plantar fascia is inflamed or painful.

Causes of Plantar Fasciitis

Causes can include one’s bone structure, muscle tightness, being overweight, achilles tendon tightness, overuse, incorrect training, and inadequate foot wear (Petraglia et al., 2017). Like with stress fractures, some factors can be changed, and others cannot.

Treatment of Plantar Fasciitis

Treatment can vary, and may include modification of practice schedule, improvement in body mechanics during sport, change of foot wear or foot inserts, laser therapy, massage, pain medication, and ultrasound.

Your physical therapist can assess posture and body mechanics to determine the best course of action.

When to See Your Doctor and When to Rest

When it comes to injuries, it’s important to know when to seek medical advice, or when to take a rest day.

Make an Appointment ASAP

If you are unable to bear weight though your foot/leg, or can only walk with limping, please seek immediate help from urgent care, your primary care physician, or orthopedic physician. This also applies for pain with palpation (touching), swelling, and pain that has increased over time.

If you are unsure in any way if it is okay to continue playing, seek professional medical advice rather than advice from teammates, coaches, or even parents who have “seen this type of injury before”.

Athletes can be known to push through the pain, in hopes to minimize time lost from sport or avoid letting down their team. However, this perseverance can potentially worsen the existing injury, resulting in even more time lost from sport.

Consider Resting

On the subject of rest, the same concept of not wanting to lose time from sport applies. The best advice I can give you here is to listen to your body. When something is hurting, do not ignore it, do not try to play through it.

With demanding practice schedules and competitions combined with hectic daily life, athletes are prone to being overworked and getting over use injuries. Taking a day off during the week, especially when you are hurting, can be beneficial for your body to heal.

If you don’t think the pain warrants a visit to a professional, notify your coach or parents and have an honest conversation with them about the pain level, type of pain, and frequency to decide the best course of action.

Incorporating cross traininginto your schedule can be beneficial as well. Cross training can include anything active that is not your sport. Some examples are: walking, biking, swimming, dancing, yoga.

So You Have an Ankle Injury, Now What?

First and foremost, listen to your physician and physical therapist. Their timelines for the healing process may not be what you want, but recovery protocols are based off of the body’s rate for healing, and you can’t rush nature!

If you have been advised by a medical professional to refrain from activity, use crutches, use a boot, or are given exercises to perform at home, PLEASE follow their recommendations.

Use this time off the court to continue to improve in your sport, helping your teammates, or improve in other areas of your life. Here are a few ideas to get you started:

• Watch footage of yourself, your team, or other athletes playing your sport. You’ll be surprised what a change in perspective can teach you.
• Attend practices and observe your teammates. You may learn something about the way they play, or you may be able to give them advice to improve their game.
• Come up with ways to raise funds for your team, get creative!
• Focus on a class you’ve been neglecting.
• Put time into a relationship with a friend or family member.
• Start a new hobby or passion project.

If you want to prevent future injury, once you are cleared for physical activity, take a look at the exercise section below for proven, evidence based exercise and training tips.

Exercises to Prevent Ankle Injuries

This is the part you’ve all been waiting for (or possibly just scrolled to). Here are three major components to add to your training regimen that will improve your ankle stability, and thus, prevent injury.

Proprioceptive Training (Balance)

Proprioception is just a big fancy word for knowing where your body is in space. We have little receptors in all of our joints that signal our brains as to what position the joint is in at all times. Even though we aren’t consciously thinking about this all the time, our brains use this information constantly, and especially when springing into action.

When we improve proprioception, we are more in-tuned with our bodies, and our brain can signal the muscles it needs for action in a more efficient way. This is especially important for ankle injury prevention since this joint may be more prone to injury.

How Do I Start?

We train proprioception of the ankle by what we typically think of as balance training. This usually will consist of exercises that involve standing on an unstable surface and/or standing on one foot.

Start out with simple, stationary exercises and then as you master those, progressively challenge your balance. Proprioceptive training should be done for 3-5 minutes at a time, every day.

Examples of Proprioception Exercises:

• Stand on one foot on a solid floor for 30 seconds
  • Once you can do this without falling or wobbling, add in closing your eyes.
  • Then, add another person giving your gentle nudges (perturbations) to your shoulder/upper back area
• Perform single leg exercises (see section below for how-to)
  • Single leg dead lifts
  • Lunges
  • Single leg bridge
  • Single leg hop
• Dual-task exercises
  • Stand on one foot while tossing a ball
  • Walk heel-toe while passing a ball
• Go Barefoot
  • Performing exercises (in a safe environment) without shoes will provide your foot with less stability, thus, making the muscles work harder
  • Disclaimer: do not be that person that takes off your shoes in a gym, thanks.
• Add in equipment for an extra challenge
  • After mastering the basics, consider adding a compliant surface, meaning something to stand on that is less stable than the floor
  • See the list below for equipment that may be helpful in challenging your balance and improving the proprioception of your ankles.

Equipment:

• BOSU – a multi-use piece of equipment that is excellent for balance training and resembles half of a yoga ball. It can be used as shown, or flipped upside down for more of a challenge
  • Example exercises include squats, lunges with one foot on BOSU, and standing on one foot while tossing a ball

Check Out Current Prices On BOSU

• Wobble board – a circular wooden board with a protruding smaller circle on the bottom that has been used in studies such as one by Verhagen et al., 2004, which showed a decrease in ankle sprains when used before practice.
  • Caution should be used with players with pre-existing knee injuries
  • Example exercises include standing still on wobble board with eyes closed or tossing a ball to a partner

Check Current Prices On Wobble Boards

• DynaDisc – this 13.5 inch disc is filled with air and allows only one foot to be placed on it
  • Example exercises include lunge with front foot on DynaDisc and balancing on one foot

Check Current Prices On DynaDiscs

Technical Training

Biomechanics is the study of how one’s body moves during a certain action. Even small differences in how a movement is performed can affect how forces are placed on structures and may increase risk of injury. With technical training, we focus on the body’s biomechanics during the basic skills such as serving, blocking, and attacking.

For the ankle specifically, this will consist of perfecting strategies of jumping, landing, running, cutting (changing directions quickly).

Jumping and Landing

When you jump as high as you can, the forces during landing that go through your ankle, knees and hips can be up to 5 times your body weight (Tillman et al., 2004)! So landing techniques are beneficial to learn if the athlete is to prevent injury from these impactful, repetitive forces in sport.

Even greater force can be put through the leg joints if an athlete lands with one foot before the other or with their knee(s) straight. These are two key points to evaluate with your landing. These can also increase risk of knee injury (Tillman et al., 2004).

Have a friend record your landing from both an attack and a block with the slow motion setting on your phone camera. Get two angles: from the side and from the front. Watch closely for the following to see what may need to be improved:

• One foot lands before the other
• Knees are straight when feet make contact with the floor
• Feet are closer together than the hips
• Toes point inwards
• Knees “cave in” towards each other, or touch
• Heels do not touch the ground (athlete stays on balls of feet)

In no way is this an all inclusive list of biomechanical flaws with landing, but it should be a good start to improving!

Reasons Athletes May Have Poor Landing Techniques

Often, flaws with landing result from weakness somewhere in the leg(s). A professional, such as a physical therapist, can help you identify which muscles to strengthen based off of what flaws are observed.

On your own, you can aim to improve landing by jumping from a higher surface such as a park bench or bleachers. The point of this exercise would not be to jump high or far, but to focus on a soft, even, consistent landing. You could record yourself or have another person watch each landing and give you feedback.

Approach Technique for Hitters to Prevent Ankle Injury

An important tip for attacking: jump up vertically, rather than out towards the net. This will help to prevent landing on the center line, where most ankle injuries occur. This has been shown in two separate studies (Bahr et al., 1997, and Stasinopoulos, 2004) to reduce the occurrence of ankle injuries. Though this is not always possible in a game scenario, but making an attempt to avoid landing on the center line is a safe practice for yourself and the blocker.

Running and Cutting

In the sport of volleyball, an athlete typically isn’t running far, or rather doesn’t have much space to actually run. However the volleyball athlete does need to move quickly around the small court, requiring fast and agile running and cutting movements.

Drills that include fast explosive movement will require the precursor of ankle proprioception (balance) and strength to be performed correctly. Make sure you tend to those areas first if your movements are not as fast as you would like.

Using the Agility Ladder for Running and Cutting

The agility ladder is a great place to start for technical training of running and cutting. There are countless patterns of movement to perform with the ladder, and the faster you go, the harder it will be to maintain accuracy.

Agility Ladder Drills to Get You Started

Using Cones for Running and Cutting

Using cones as markers can be helpful with short running drills. As with the agility ladder, there are endless formations and routes to run forwards, backwards and sideways to improve agility.

Cone Agility Drills to Get You Started

Do Not Neglect the Knees and Hips

Simply put, weakness at the hips and knees can affect how force moves through the ankle during sport. These forces have the potential to cause injury. Strengthening the whole leg allows the athlete to dissipate forces to prevent injury on any one body structure.

Leg Exercises

Performing a variety of leg exercises, and adding additional weight where appropriate, can help improve strength throughout the entire leg. Here are a few to get you started:

• Bridges
  • Double leg
  • Single leg

• Squats
  • Body weight
  • Jumping
  • Sumo (spread feet wide apart and toes pointing out 45 degrees)

• Lunges

• Dead Lifts
  • Single leg
  • Double leg

• Kettle Bell Swings

• Calf raises

Gym Equipment

Additionally, gym machines that target specific muscles can help to isolate muscles and strengthen them individually. Usually they have pictures on the machine that tell you how they should be used. Start with a light weight and ask a gym attendant for assistance if needed.

Some to look for, or ask a gym attendant for, next time you are at the gym:

• Knee extension (quads)
• Knee flexion/curl (hamstrings)
• Abduction/Adduction machine (glutes and inner thigh)
• Calf raise (gastrocnemius and soleus)
• Leg press (quads, glutes)

Braces, Taping and Shoes, Oh My!

Braces

The evidence shows that bracing is much more effective at preventing ankle sprains in athletes who already have prior injury (Kaminski et al., 2013).

If you have had ankle injury, bracing is a good idea.

If you haven’t had an ankle injury, it may not be worth the cost, but bracing won’t decrease the quality of your performance.

Wraps and Sleeves

First, let’s point out the kind of ankle braces that won’t prevent injury. The two main types that fall in this category are wraps and sleeves. These might be better for wearing after an injury to decrease the swelling in the ankle, but are NOT suggested for the purpose of preventing injury.

Braces for Injury Prevention

Now, we can move on to braces that can actually prevent injury. There are many options when choosing an ankle brace. As a PT, I have extensive education of the ankle anatomy and mechanism of injury. With that said, I have used this knowledge to pick out ankle braces that have rigid supports of both sides of the ankle to prevent sprains. This list in no particular order.

• Active Ankle T2 Ankle Brace

• Aircast Air-Stirrup Ankle Brace

• Bionic Stirrup Ankle Brace

Bracing is just one component in ankle injury prevention. The athlete should not ignore the importance of incorporating ankle and leg strengthening (as seen in the section above) in preventing ankle injury.

Does Taping Really Help Prevent Ankle Injury?

This is a tough question to answer because there are so many different types of tape and taping techniques. Additionally, some of the scientific evidence says taping does prevent injury, and some say it inhibits athletic performance.

There is a suggested psychological benefit to taping. When you have a tape on, it stimulates the touch receptors on the skin and constantly sends signals to your brain. This constant signal can serve as a reminder for the athlete to be more “careful” when using their ankles for jumping, landing, running or cutting.

It may also help with proprioception of the ankle as discussed in the above section (where your ankle is in space). Thus, possibly improving balance or bodily awareness (Murray, 2001).

If you do choose to tape, have it done by an athletic trainer or physical therapist who is experienced or has certification in taping techniques. A bad taping technique might as well be no tape.

Overall, taping may be more costly, time consuming, and less effective than bracing. It is much more common to see volleyball players with ankle braces than taping techniques applied.

Volleyball Shoes

Shoes are very much a personal preference and sometimes can be trial and error with the individual. When trying on shoes, makes sure to simulate actions you will be performing in those shoes such as jumping high and running and few feet, then stopping. Here is a short list of preferred brands recommended by experienced volleyball players who were informally surveyed.

• Mizuno

• Asics

• Nike

References:

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Bahr R, Bahr I A. Incidence of acute volleyball injuries: a prospective cohort study of injury mechanisms and risk factors. Scand J Med Sci Sports 19977166–171. 

Bahr R, Lian O, Bahr I A. A twofold reduction in the incidence of acute ankle sprains in volleyball after the introduction of an injury prevention program: a prospective cohort study. Scand J Med Sci Sports19977172–177. 

Bicici S, Karatas N, Baltaci G. Effect of athletic taping and kinesiotaping® on measurements of functional performance in basketball players with chronic inversion ankle sprains. Int J Sports Phys Ther. 2012;7(2):154‐166.

Kaminski TW, Hertel J, Amendola N, et al. National Athletic Trainers’ Association position statement: conservative management and prevention of ankle sprains in athletes. J Athl Train. 2013;48(4):528‐545. doi:10.4085/1062-6050-48.4.02

Mayer SW, Joyner PW, Almekinders LC, Parekh SG. Stress fractures of the foot and ankle in athletes [published correction appears in Sports Health. 2015 Nov;7(6):557]. Sports Health. 2014;6(6):481‐491. doi:10.1177/1941738113486588

Molinari A, Stolley M, Amendola A. High ankle sprains (syndesmotic) in athletes: diagnostic challenges and review of the literature. Iowa Orthop J. 2009;29:130‐138.

Murray HHusk L. Effect of kinesiotaping on proprioception in the ankle. J Orthop Sports Phys Ther. 2001; 31: A-37

Petraglia F, Ramazzina I, Costantino C. Plantar fasciitis in athletes: diagnostic and treatment strategies. A systematic review. Muscles Ligaments Tendons J. 2017;7(1):107‐118. Published 2017 May 10. doi:10.11138/mltj/2017.7.1.107

Reeser JC, Verhagen E, Briner WW, Askeland TI, Bahr R. Strategies for the prevention of volleyball related injuries. Br J Sports Med. 2006;40(7):594–600. doi:10.1136/bjsm.2005.018234 

Stasinopoulos D. Comparison of three preventive methods in order to reduce the incidence of ankle inversion sprains among female volleyball players. Br J Sports Med. 2004;38(2):182‐185. doi:10.1136/bjsm.2002.003947

Tillman MD, Hass CJ, Brunt D, Bennett GR. Jumping and Landing Techniques in Elite Women’s Volleyball. J Sports Sci Med. 2004;3(1):30‐36. Published 2004 Mar 1.

Verhagen E, van der Beek A, Twisk J.et al The effect of a proprioceptive balance board training program for the prevention of ankle sprains: a prospective controlled trial. Am J Sports Med 2004321385–1393. 

Verhagen E A, Van der Beek A J, Bouter L M.et al A one season prospective cohort study of volleyball injuries. Br J Sports Med 200438477–481.

Verhagen, E. A., van Tulder, M., van der Beek, A. J., Bouter, L. M., & van Mechelen, W. (2005). An economic evaluation of a proprioceptive balance board training programme for the prevention of ankle sprains in volleyball. British Journal of Sports Medicine, 39(2), 111–115. doi:10.1136/bjsm.2003.011031