Updated: May 29, 2020
Segmental net force is a measure of the sum of the instantaneous forces acting upon the segment. This includes internal myofascial forces generated both to accelerate the segment but also those that are acting to decelerate the segment. The first of these would increase the total net force and the second decrease it. Alongside this are external forces that act upon the segment such as gravity and air resistance. Adding all these forces together results in the net segmental force.
It should be remembered that an internal muscular force that acts to accelerate a more distal segment of the body may at the same time apply a force to a more proximal that decelerates it. An example of this is the contraction of the obliques and pull on the associated fascia to accelerate the thorax which at the same time also decelerates the pelvis. This can be seen in the diagram below.
When we consider the force acting on the club the measurement takes into account not only the force that the wrist movement is imparting but also the centripetal force that keeps the club moving in a curved path, the golfer’s pull on the club as well as gravity and air resistance.
The peaking of all segmental forces that we see at impact in good players shows the highest total force in the system occurs at that point. It is important to remember through that not all of this force will be applied to the club ball collision.
The net force is the sum of all the forces that may be acting on the body. What is important to acknowledge is there are many restrictions around calculating force through the use of motion capture as some of the forces that influence segmental and club force we cannot measure through 3D. The mathematical model used to calculate each segments centre of mass is extremely robust however we fully accept and acknowledge there are many limitations around using 3D to calculate force. However based on what we can produce despite hardware limitations, these values provide a good understanding of the resultant force being produced by each segment.
Golf club force.
For the club the forces that are acting on it while in swing, it is important to understand what forces the club is being subjected to:
Force applied by the player in accelerating the club. This force is due to moving of the hand.
The force due to gravity on the club mass.
The centripetal force responsible for keeping the club moving in a circular/ curved path.
The stress and shear on the club shaft.
The force/drag on the club due to air and viscosity.
Each of these forces can be acting on the club in different directions. The resultant or sum of these forces is responsible for the acceleration of the club. If all these forces sum to zero the club will not accelerate.
We only measure point one above.
If you would like to understand further how force is calculated and applied in 3D, here is a good link that may help - http://www.physicsclassroom.com/class/vectors/Lesson- 3/Addition-of-Forces
Important acknowledgement and thanks - A huge thank you to Matt Bridge for helping produce this document and his time and effort in creating more understanding of these values.