This newsletter focuses on the kinetic chain principle and it’s application in human movement. What is it, how does it work, and why is it useful?
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What is the kinetic chain principle?
The kinetic chain principle is an engineering concept.
It is used to explain how a series of connected segments generate and transfer momentum between each other when moving.
This sounds complicated!?
Bear with me…
So how does this relate to human movement?
Well… the body can be considered as a series of connected segments.
Each limb is a segment connected by tendons and muscles. These play specific roles in generating and transmitting momentum to perform movements.
This concept can therefore help us understand theoretically how the body should move to produce consistent and fast movements.
This can help us improve performance, as well as, help reduce the risk of injuries.
It should be noted, however, that this comes with a caveat.
The kinetic chain principle provides a generalised technique which conforms to physics and fails to consider the unique individuality of the human body.
It is important to remember, that this technical movement pattern will vary based on individuality.
So while it provides us with an idea of what good theoretically looks like, we must remain wary that it may not be optimal or achievable for every individual.
How does it work?
The whole concept is based on Newton’s Laws.
Newton’s first law highlights that some objects are harder to change the motion of than others. This concept is also referred to as ‘inertia’.
Newton’s second law states that how quickly an objects momentum changes depends on the net force acting on the object.
Now this can be a bit tricky to visualise or describe with text…
But if the same force is applied to two different objects with different inertias, this law states the change in momentum of each object will be the same (often known as the conservation of momentum).
Since momentum is defined as the product of inertia and velocity… the only way the change in momentum can stay the same when the inertia of the object changes, is for the the velocity to change to conserve this relationship between force and momentum.
A few years ago, a coach asked if a Newton’s cradle was a good example of this… which it is (mostly) and ever since I have been using this video (from 2.05 onwards) to help explain this law…
As the inertia of the bead changes, the velocity of the beads change to maintain the momentum!
Newton’s third law states that for every action force, there is an equal and opposite reaction force.
In a kinetic chain, these combine and can help us understand the theoretical optimal movement pattern for maximal efficiency and end-point velocity (e.g. kicking, throwing, striking).
In the body, the proximal (closest to the centre of the body) segments have greater inertia than the distal segments (furthest away from the centre of the body).
This makes them good for stability and for developing initial momentum within movement patterns…but not so good for moving quickly.
The distal segments with their smaller inertias are better designed to move quickly.
Rather than moving these distal segments individually, the kinetic chain principle indicates that the segments all contribute…
The momentum generated in each segment can be transferred in a proximal to distal sequence with the transfer occurring when the proximal segment best aligns with the task outcome (e.g. running location, throwing target, or hitting direction).
If you go back to the video above, we can think of these beads as representing different segments of the body – the momentum is initially developed in the big proximal segment and then transferred to the smaller distal segments to maximise velocity…
The importance of alignment can be seen when the distal bead initiates the reverse distal to proximal sequence and the lack of momentum that transfers back through to the distal bead.
This is a good example of how we can reduce or dissipate momentum, but care needs to be taken in humans that the body is designed to dissipate the momentum in that direction.
In general, the kinetic chain principle is often summarised into the following key principles for human movement:
- Stability – proximal body segments should provide a solid base of support to allow for a effective and efficient transfer of momentum to the distal segments
- Proximal-distal sequencing – initial momentum should be generated in the proximal segments, before generating and transferring momentum to the distal segments
- Alignment – the transfer of momentum from the proximal to distal segment should occur when the proximal segments momentum best aligns with the task outcome
Why is it useful?
In sporting movement patterns, the sequencing and timing of the generation and transfer of momentum between segments is key in optimising performance and minimising injury risk.
The kinetic chain principle provides a framework for movement patterns to be broken down and assessed theoretically.
Most movements conform to a sequence of phases based on the key principles of human movement. For example…
- Initial phase – initial momentum is generated in the proximal segments
- Preparation phase – initial momentum of the proximal segments is stabilised to provide a base of support, while the rest of the body is organised ready to maximise the proximal to distal sequencing
- Transfer phase – momentum generated and transferred into a proximal to distal sequencing when the segments best align with the outcome
What about the follow through?
This phase is often not considered when thinking about performance, but it crucial that stability of the proximal segments is maintained since this provides the base for the next movement task.
To dissipate momentum, the same principles can be applied in reverse.
The momentum in the distal segments can be transferred in a distal to proximal sequence (see video above).
Care needs to be taken, however, that the body is designed and capable of dissipating momentum in that direction.
That’s all for this month
To recap:
The kinetic chain principle is an engineering principle which allows us to think about the body as a series of connected segments.
This leads to the following key principles for human movements:
- Stability – proximal body segments should provide a solid base of support to allow for a effective and efficient transfer of momentum to the distal segments
- Proximal-distal sequencing – initial momentum should be generated in the proximal segments, before generating and transferring momentum to the distal segments
- Alignment – the transfer of momentum from the proximal to distal segment should occur when the proximal segments momentum best aligns with the task outcome
These can be used to help provide an initial theoretical framework to analyse sporting movement patterns.
It is important to remember, however, that movement patterns vary based on individuality, so while it provides us with an idea of what good theoretically looks like, we must remain wary of what is achievable for a particular individual.
Thanks for reading.
Paul
The Cricket Biomechanist 