If there is a weakness in the chain, the transfer of force does not occur properly, resulting in both a loss of power as well as extra stress being placed on joints such as the knees. These weaknesses often show up in faults such as a valgus knee and excessive pronation.
By Nick Burrows, Exercise Physiologist
You may have noticed that we have recently added a new set of tests to our movement assessment where we have been getting our athletes to perform single leg jumps. While some impressive distances have been seen, what we are actually looking at is any disparity between the two legs. So why is single leg jumping so important?
When we perform a dynamic movement with our lower limbs such as running or jumping, the leg acts as a chain for transferring force, something we call a kinetic chain. Basically when the foot lands, the force of our body on the floor is transferred up our legs to our hips where it is absorbed by our gluteal muscles and can be transferred back down the leg for another step.
So the first thing we are looking at with the single leg jumping is how you land, particularly how your knees and ankles react. The second thing we look at is if there is a difference between the two legs. The reason a difference is important is that very little of what we do is with one leg in isolation. Whether it is running where repetitive single leg jumps are performed by alternating legs, or two legged jumps such as box jumps or olympic lifting. Obviously if one leg is significantly stronger and more stable, then we will favour it when performing these movements which will often show up as overuse injuries. Interestingly niggles and pains often show up in the stronger leg as it is picking up the slack.
So what can we do to improve our single leg dynamic stability? Obviously the first port of call is to ensure we have appropriate static stability, i.e. we can perform single leg balance tasks such as the drinking bird and slider lunges. If that is the case we begin by performing some simple landing tasks. Start with a low step and hop off the step landing on the middle of your foot and making sure you keep your pointing forwards and hips parallel. Once you have mastered this add in a small hop to simulate the re-transfer of force into another jump.
Once you can successfully land, stabilise and jump in one plane of movement it’s time to add in some lateral movements. We use a four square jump progression. Find a cross on the floor, maybe a junction of tiles or floor boards and hop in a square around the cross all the way round, then go back the other way. Make sure you stabilise and control at each point, don’t let your knees bend in or hips tilt to one side. If you can land, control and jump off again in all four directions with both legs it will go a long way to improving performance and preventing overuse injuries.