Posted on August 14, 2015 by Jenny Cromack
Biomechanics of Running Part 1
Joint Mechanics
The first part of this blog series identifies key points during the phases of running in relation to the joint positions and mechanics and highlights some common faults. The second blog will look at the muscle actions during each phase of running.
Running Phases
Stance Phase
Initial Contact
This is the first moment one foot makes contact with the ground and this is where the forces are absorbed and the foot is prepared, and loaded by the calf and Achilles, for the next phase. Between the initial contact and the toe off phase the stance is reversed so the other leg enters its swing phase ready to make the next initial contact.
Toe Off
This is at the end of the stance phase and involves the release of the elastic energy allowing the foot to propel the body upwards and forwards.
Swing Phase
This is where the foot leaves the floor (behind the body) and is propelled forward ready for it’s next initial contact (in front of the body). Just after the toe off there is a phase where both feet are off the ground known as a double float.
Hip Mechanics
The hip is at the ‘top of the chain’ so if the movement at this point is out then it will ‘domino effect’ down through the knee and ankle. Generally the hip extend through the stance phase and is then flexed through the swing phase. As this cycle of extension-flexion occurs we need to reduce excessive adduction and abduction (inward and outward movement) and keep the hip neutral help with the position of the knee and ankle. As well as this we also need to consider the rotation of the femur and the hip.
The hip should be maintained in relatively neutral rotation during the stance phase and initial contact, if the hip internally rotates it can cause the knee to collapse inwards, which pronates and flattens the foot. This can cause injuries to the knee, ankle, and foot. The neutral rotation should be maintained as the foot contacts the ground which will help maintain proper knee tracking and foot position as you transition through the stance phase and through the toe off into the swing phase. As you transition through the swing phase the hip may externally rotate slightly so that the foot is in a good position to strike the ground on the outer edge of the mid-foot and absorb the ground reaction force during contact.
As well as the hip rotation the level of the hips and pelvis needs to be considered. Ideally the level of the hips and pelvis wants to be inline (horizontally). Usually in those who have a weakness around the hips, during their stance phase when the foot strikes the ground the opposite side hip and pelvis will drop. This can cause a collapse of the knee and ankle inwards.
Knee Mechanics
The knee joint has limited movements in comparison with other joints but when running it is important to consider the knee movement in relation to the foot. The knee itself goes through extension-flexion cycles (straightening-bending). On the stance phase where the initial contact occurs the knee starts to extend, but it shouldn’t be fully extended and locked out as this can stress the ligamentous structure and reduces the ability to absorb the forces of ground contact.
The important consideration in this phase is the tracking of the knee. During the stance phase where the forces are absorbed and transferred the knee should track straight over the second toe. The common fault in people is that the knee will track inwards more towards or inside the big toe. This places a great deal of stress through the ligaments and structures within the knee. From the point of toe off the knee then starts to flex as it swings through to the next contact and stance phase. It then starts to extend in preparation for the next contact.
Foot Mechanics
When running the contact forces that run through the foot can reach approximately two and half times your body weight. This makes its very important that at this point of contact your foot is in the best position to absorb these forces and minimise the stress that is transferred up through the leg.
There is a misconception that making initial contact with the heel is the best way to run, this in fact is where the contact forces are at their highest. This is not to say that you should overcompensate and start striking the ground at the forefoot. This can also create a lot of force transfer through the leg but I have also found that those who forefoot strike tend to suffer from a lot of calf and Achilles complaints.
For an ideal foot strike and force transfer it is suggested than landing on the outer edge of mid-foot with the ankle in a neutral position or slight dorsiflexion is optimal for minimising force peaks. The toes should be pointing forwards to minimise the internal rotation of the lower leg. As the foot strikes the ground the foot the rolls slightly inwards, into pronation to unlock the foot and absorb the contact force. As this occurs the calf and Achilles are set up to load the foot ready for the ‘toe off’. This loading occurs via the stretch-reflex of the calf and Achilles, so when we strike the ground and the calf is stretched through the loading of the foot it stores up elastic energy and on the toe off this energy is released.
On the toe off the elastic energy of the calf and Achilles is released and the body is propelled upwards and forwards through ankle plantarflexion (pointing of the foot downwards) and extension of the toes. The swing phase then begins and the ankle is dorsiflexed so the foot is lifted to clear the floor as the leg swings through before then preparing for its next contact.
Summary
The mechanics of running is important in reducing the likelihood of injury and optimising force production. Working from bottom to top the hip should be maintained in relatively neutral rotation, with minimised adduction and abduction moving in a straight front to back plane of motion. The levels of the pelvis also needs to be maintained. This will then in turn help keep the knee tracking directly over the second toe and in a neutral flexion-extension cycle. With the hip and knee working in optimal alignment this allows the foot to strike the ground in an optimal position, making contact on the outer edge of the mid-foot and rolling into pronation to absorb the force. The ankle can then plantarflex and propel the body into the next phase.
Check out the next blog for the muscular contractions that occur during the phases of running.