In last month’s issue we explained muscular loading. This month we are going to explain the most important foundation of the kinetic link which initiates muscular loading: Ground Forces.
No single link in the process of creating clubhead speed is considered more important than any other; however, your swing is only as strong as your “weakest link”. During the golf swing, the transfer of energy and power from the lower body to the upper body is certainly the most pivotal, and thus the most common “weakest link”.
The role of the trunk musculature in the golf swing is the same as the role of a crank shaft in an automobile. Just like the crankshaft turns horsepower created at the drive wheels, the trunk musculature turns energy created by the lower body into power at the upper body. This in turn creates clubhead speed. With maximum energy transfer comes maximum power.
Just like a house, a solid golf swing must be built on a solid foundation. That foundation is lower body mechanics or ground forces. The movement of the lower body is composed of both Linear components and rotational components. It is this proper interaction between the two that creates a stable basis for the rest of the swing.
Your feet generate forces when they push against the ground. These forces act to propel your body and create motion. There are two kinds of forces that are important to the golf swing: Normal and Shear forces. Normal forces are used to define the linear component of the swing. Shear forces are used to define rotational forces of the swing.
The Linear Component
Normal force is applied by the feet downward or perpendicular to the ground (see Figure A). Weight is transferred to the back foot during the backswing and to the front foot during the downswing. When weight is shifted to one foot, the amount of normal force applied by that foot increases, while the normal force applied by the other foot decreases. This action defines the linear component of movement. The linear component of the lower body during the swing is very important, because from this movement that the body develops momentum and enhances the rotational speed and power the hips.
Rotational Forces
Shear force is applied by the feet along the surface or parallel to the ground (See Figure B). Throughout the swing, shear forces are being applied by both feet. These shear forces create torque that turn the hips around the axis of the trunk. This defines the rotational component of the lower body movement. The rotational component provides the basis for power during the golf swing and can be the most directly related to ultimate clubhead speed.
Faults in Energy Transfer
The most two common breakdowns in transferring energy from the lower body to the upper body originate with the hip segment.
The first of these is called sliding hips, which occurs when the hips move laterally to the left without rotating. No rotational speed is created. Muscles aren’t properly loaded and there is diminished energy created to be passed to the upper body. In many cases, sliding hips also indicates an excessive spine tilt. When the spine tilts, muscles that work to rotate segments around the axis of the spine become asymmetrical in that one shortens and the other side lengthens. This asymmetry cause inefficient generation of power or speed and can cause increased stress on the back and joints, resulting in back injuries.
The second is called “spinning hips” which occurs when the golfer forces the hip segment through the swing too quickly. This creates excusive lag between the lower body and the upper body. The upper body typically never catches up. The trunk musculature is never used to pass energy created by the hip segment rotation to the shoulder segment which means lost power and lower club head speed.
By building a solid foundation from the ground up, and then working on the efficient transfer of energy from the lower body towards the upper body, you can effectively increase power, distance and accuracy throughout your game.
Scott Beaumont is from ZenoLink. ZenoLink is a diagnostic tool that used 3D motion analysis for coaches to be able to measure their athlete’s biomechanical breakdowns in their golf swing. By measuring hip speed, arm speed, shoulder speed, club release speed and club linear speed, ZenoLink creates separate analyses of kinetic linking, stability, muscular loading and club dynamics; helping a coach or instructor identify functional movement discrepancies that rob the player of power, and to design a personalized Progressive Skills Training program that addresses problem areas. 
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