Running 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.
Stance phase - the foot is in contact with the ground
1. Initial contact
One foot (say left) is about to touch the ground, while the other foot (right) is off the floor (in swing phase).
2. Braking (absorption)
As soon as your left foot touches the floor, your body is performing a controlled landing (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, the tendons and connective tissue within the muscles store elastic energy for use later in the propulsion phase.
There are two braking here - horizontal and vertical. For better efficiency, we want to reduce both:
- To reduce horizontal braking, one can reduce the vertical hopping. It is hard to do, but you can think of a smoother run.
- To reduce vertical braking, one should avoid over-striding. Also, try to pull the foot backwards to keep the relative speed of the foot to be close to zero to reduce such braking. (consider some drills)
3. Midstance
When 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.
Pay attention to when the maximum force is used - if it is before the midstance, you are likely braking too early/too much in the previous phase.
The ground reaction force at the centre of pressure have been shown to increase to 250% of the body weight.
4. Propulsion
The left leg 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 three components (ankel, knee, hip) consists the main system for braking/storing/propulsion, but it varies dramatically how force is distributed (research shows that >50% of the elastic energy comes from the Achilles and tendons). The distribution is critical for efficiency and injury.
Swing phase - the foot is not in contact with the ground
The leg travels freely backwards, and swing. The height of the heel and the returning drive of the knee depends on the power of hip extension and speed.
In general, we want the swing to be driven by knee (not dragging the leg back), while keep the knee and ankle relaxed. Because of the relaxed knee, the foot with naturally swing higher when in higher speed, which reduces the radius (centered at the hip), allowing faster return to the front.
Upper Body Mechanics
Balance is achieved by arms and upper body working in the opposite direction to the legs.
Faster arm swin can also increase the cadence.
Diagonal elastic support mechanism
One’s upper body have diagonal muscles. When stretching upper body diagonally in each step, arm swing, shoulder and upper body rotation stores elastic energy in these muscles, and then releases and distribute throughout the body.
As a result, a well functioning central core area allows such force distribution efficiently.
Kinetic Chain
TODO - add more defails.
It is a much more complex topic, where the whole body is considered.
Running requires:
- Balance
- Muscle strength
- Joint range of movement
During the running gait cycle, the ground reaction force (GRF) at the centre of pressure (CoP) have been shown to increase to 250% of the body weight.
Efficiency
The key takeaway here is efficiency and injury-free.
In most cases, you want to consider your body a fine tuned machines with a lot of moving parts connected by springs. Every stride will generate, absorb and release energy. The most you can recycle from the previous movement, the more efficient it is. Our body archieves this using various tedons, muscle and issues, while keep our movement within certain range with frequency.
Also, while trying to be efficient, every part of our body has its limit. We also want to avoid over-use to avoid injury, even certain movements can be more efficient. One example is over-use our ankle/Achilles, which is the best energy/shock absorption component. Excessive use of Achilles can also lead to injury.