Tuesday, 11 September 2012

Overstriding in runners

Some quick thoughts today on overstriding in running. Overstriding in running is common, even in the more elite runners. It’s a hot topic at the moment with the advent of minimalist running shoes and the barefoot community pushing their side. Striking mid foot and fore foot has become the new ‘trend’.

So, how do we define an overstride? Overstriding is basically where you land outside your centre of mass, ahead of your body if you like. There are a couple of things that are usually apparent with overstriding;

1.    Posterior pelvic tilt
2.    Heavy heel strike (as opposed to a light or glancing heel-strike)
3.    Greater knee extension (meaning more work from the quads)
4.    Larger braking forces (deceleration)
5.    Considerably more work from the calves to ‘propel’ the runner
6.    More time on the ground (slowest portion of the gait cycle)
7.    Slower cadence

With all of this going on it looks to increase your injury risk profile. It is definitely less efficient and slower in nature. The key point is how do we recognise this and how do we change this. Does it really matter whether we mid foot or fore foot strike? Let’s look closer at each point.

Posterior pelvic tilt is one of the most common things occurring in distance runners with greater prevalence in the more mature athlete. As soon as this happens your sacrum is thrust into a position known as ‘counter-nutation’ effectively limiting your ability to extend your hips. This position shuts down the powerful glute and hamstring muscles from their ideal firing position. The propulsion is therefore gained from quads and calves.

Posterior pelvic positions leave the lumbar spine vulnerable to loading forces – especially the sacro-iliac joint and discs. The first thing you need to do is get your pelvis in a neutral to (slight) anterior tilt, without this it’s very hard for the lower limb and foot to be in a biomechanically correct position!

Heel striking is not inherently bad, it is more how you do it rather than if you do it. As you fatigue, heel striking becomes the preferred position. Even the great Haile Gebrasalasie ran in a glancing heel strike position towards the end of the marathon. The key point here is to try and keep your cadence a little shorter, allowing your foot strike to land closer to your centre of mass. This results in a quicker and lighter foot strike with lower braking forces and usually a strike that is more toward a mid-foot strike.

Greater knee extension occurs in relation to the posteriorly rotated pelvic position. Lack of glute and hamstring firing necessitates increased extension at the knee joint to lengthen the stride, simultaneously increasing lower extremity loading as the heel strikes the ground in a straightened (knee extended) position. To change this, you need to address the pelvic position.

Deceleration (braking) forces occur during heel strike outside the centre of mass with the foot in a strong dorsiflexed position. This creates a collision impact with opposing forces as opposed to the foot contacting the ground in a rotary motion. This rotary motion uses the ground to propel and push off allowing acceleration to continue through the full gait cycle. This allows the use of the elastic energy stored in the myotendinous unit through the stretch-shortening cycle.

With deceleration occurring the calves are forced to accelerate through mid-stance to toe off over a longer period of time, hence there will be larger forces acting on the lower limb. Due to the longer contact times the runner will be slower through their stride (the slowest portion is the time on the ground, more time on the ground equals slower stride).

Mid foot and fore foot striking is the new ‘trend’. A foot strike of this kind is not necessarily better. What is important is whether or not an overstride is present. It is not impossible to have an overstride with a forefoot strike especially if the runner forces the forefoot into plantar flexion in the belief that a forefoot strike is better! Deal with the overstride and let the foot land however it is used too.

With all this occurring it may appear as a long and lengthy period to correct.
As the body works as a kinetic chain one change can often alleviate others. Starting with the pelvic position is an obvious choice. This often helps with a foot strike closer to the centre of mass. Changing the cadence by as little as 5-10% may also assist by shortening the stride. These two changes often increase knee flexion angle on foot strike and increase hip extension.

Overstriding is a common problem that can be addressed in a step by step fashion. The most important factor is whether you end up striking close to your centre of mass, not whether you heel strike or not.

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