The Science of Ankle Sprains
Ankle sprains involve stretching or tearing of ligaments, usually the lateral ligaments (ATFL, CFL). This damages mechanoreceptors, affecting proprioception. Without proper rehabilitation, chronic instability can develop.
Contributing Factors
Most ankle sprains happen when your foot lands in an inverted position (turned inward) with your body weight shifted over the outside edge of your ankle. This classic mechanism occurs because your lateral ankle ligaments are much weaker than the medial ones, making them vulnerable when your center of gravity moves over the lateral border of your foot. The dangerous moment happens when your foot makes contact with the ground while inverted - there's simply not enough time for your muscles to react and correct the position.
Poor landing mechanics significantly increase your risk. When you land on an unstable surface or with poor body control, your foot may contact the ground in excessive inversion before your peroneal muscles can fire to correct it. Your peroneal muscles normally act as a protective mechanism, but they need about 60-80 milliseconds to respond to a sudden inversion force. Unfortunately, an ankle sprain can occur in as little as 20-40 milliseconds - much faster than your muscles can react.
Previous ankle sprains create a vicious cycle of instability. The initial injury damages the mechanoreceptors in your ligaments that provide balance and position feedback to your brain. Without this proprioceptive input, you're much more likely to land awkwardly or lose balance, leading to repeat sprains. This is why people often say their ankle "gives out" or they have a "weak ankle" - it's not actually weakness, but rather poor balance control and position sense from the damaged ligament receptors.