The study of the mechanical laws relating to the movement or structure of living organisms.
If the above has turned you off slightly, I totally understand. It’s hard to go for a run these days without worrying about where our foot is landing, what shoe we’re wearing, or optimal stride frequency.
Surely running can’t be so complicated! The good news is, it doesn’t have to be!
The first thing you can do is discount anybody out there who tells you that their way is the only way. If that were the case, all elite, world-class runners would have the same running style, and quite simply they don’t.
Question: How do you run and which of these runners in the photos below is more likely to experience low back and knee pain? Answer at the end of this article.
Running, like any sport, is a skill for which improvement will depend on suitable conditioning and active development, but it’s about building on your individual running style, as opposed to basing your training regime on what happens to work well for somebody else.
Having a basic understanding of the biomechanics of running can help you appreciate your own running form and see where you may be able to make improvements. It can also help you make more sense of what you read and hear with regards to running styles, training programs, conditioning exercises, footwear, etc.
Although running most definitely depends on whole body interaction, dividing the running stride up into individual components or “phases” can help us understand how slight changes can help improve performance and reduce susceptibility to injury.
Getting Started: The Gait Cycle
An introduction to running biomechanics can begin by looking at what we call The Gait Cycle. This cycle starts when one foot makes contact with the ground, and ends when that same foot makes contact with the ground again.
It can be divided up into two “phases” – the stance phase (during which the foot is in contact with the ground) and the swing phase (during which the foot is not in contact with the ground).
The stance phase is typically considered as the more important of the two as it is when the foot and leg bear the body weight. The swing phase is (or rather should be) passive, i.e. not consciously controlled.
Trying to actively help the leg move through the swing phase is an example of where runners can waste energy, e.g. by consciously trying to lift the heel higher towards the backside, or trying to lift the front knee higher. Let’s look at the components that make up the stance phase.
The Stance Phase
This can be divided into four stages: initial contact, braking (absorption), midstance, and propulsion.
1. Initial contact
Let’s imagine you are at that moment in your stride when both feet are off the floor (sometimes referred to as float phase). Your left leg is out in front of you and about to touch the ground. This moment (whether you land on heel, midfoot, or forefoot) is called initial contact and marks the beginning of the stance phase. Your right foot behind you is off the floor and in swing phase.
2. Braking (absorption)
As soon as your left foot makes contact with the ground in front of you, your body is in effect performing a controlled landing, managed via deceleration and braking. Your left knee and ankle flex (the opposite of straighten) and the left foot rolls in (pronates) to absorb impact forces. During this process of absorption, the tendons and connective tissue within the muscles store elastic energy for use later in the propulsion phase.
The braking phase above continues until the left leg is directly under the hips taking maximum load (maximum risk of injury) as the body weight passes over it. The left ankle and knee are at maximum flexion angle. This moment is called midstance (you may also hear it referred to as single support phase).
Now that your left leg has made a controlled landing and absorbed as much energy as it’s going to get, it starts to propel you forwards. This is achieved by your left ankle, knee and hip all extending (straightening) to push the body up and forwards, using the elastic energy stored during the braking phase above. The more elastic energy available at this stage, the less your body has to use the muscles.
The propulsion phase ends when the toe of your left foot (now behind you) leaves the ground, commonly referred to as “toe off” (TO). At this point, both of your feet are off the ground so you are once again in float phase.
Research shows that at least 50% of the elastic energy comes from the Achilles and tendons in the foot.
The Swing Phase
At the moment of toe off, your left leg has travelled as far back as its going to and the heel starts to lift towards your backside. As I mentioned earlier, this is a passive movement (as opposed to a conscious effort), with the height that the heel reaches depending on the degree of hip extension achieved and the speed you are running at.
Steve Magness, Head Cross Country Coach at University of Houston, compares this stretch reflex mechanism to the stretching back of a sling shot and then letting go. Extension of the hip (as your back leg moves behind you prior to toe off) is equivalent to pulling back on the sling shot.
Letting go results in the leg firing forwards rapidly, leading with the knee. Any conscious attempt to move the leg through the swing phase (Steve refers to it as the “recovery phase”) results in wasted energy and a less powerful firing of the slingshot.
Once the knee has passed under the hips, the lower leg unfolds in preparation once again for initial contact, marking the end of the swing phase.
Upper body and arm mechanics
The interaction between the upper and lower body plays a vital role in running, the upper body and arm action providing balance and promoting efficient movement. This balance is achieved by the arms and upper body effectively working in direct opposition to the legs. Bringing the left arm forward opposes the forward drive of the right leg, and vice versa.
During the braking (absorption) stage described above (initial contact to midstance), the arms and upper body produce a propulsive force.
During the propulsion stage (midstance to toe off), the arms and upper body produce a braking force.
By working as opposites, forward momentum is maintained. The arms and upper body also counterbalance rotation in the midsection. For example, as the right knee is fired through in front of the body (right swing phase) an anticlockwise momentum is created. To counterbalance this, the left arm and shoulder move forwards to create a clockwise momentum to reduce rotational forces.
To help the above occur as efficiently as possible, arm swing should be initiated at and through the shoulders. Driving the elbows down as well as back can help avoid elevation of the shoulders, which in itself causes tightness and limits range of motion.
Just as bringing the knee through in swing phase needs to be a passive movement, so does the forward movement of the arm. Driving your arms up and forwards wastes energy and reduces the efficiency of the stretch reflex mechanism in the shoulders. Your hands crossing the midline of the body is a sign that you may be driving the arms forwards instead of backwards, or that you have tightness in the chest.
Correcting arm crossing can increase efficiency, as can ensuring that the elbow angle only changes slightly (as a result of elastic response as opposed to active movement)
On a final note, bringing the arm too far back (or forwards) can cause excessive braking and lead to injury.
Answer to our question is that the first one is more likely to result in pain in the low back or knees – because he is putting all his weight on his heel and the leg is far from perpendicular. However, these things are, as most problems and pain, multifactorial.
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