**5. Biomechanics of the modern golf swing**

Modern biomechanics techniques have allowed a clear understanding of the physical requirements of the body for the execution of a golf swing. Simply put, a golf club made up of a stick or shaft attached to a heavier head hits a ball towards a target by swinging the stick.

The motion involves a complex manipulation of shaft and club by the golfer to promote maximum force on the ball in an effort to propel the ball towards a target. Once described by Winston Churchill as" a game whose aim is to hit a very small ball into an even smaller hole with weapons singularly ill-designed for the purpose".

The golf club exerts a force on the golf ball by creating a greater force on the down swing which is transferred to the ball. This force is a function on the mass of the club and the speed it is travelling at. This in turn is a function of the distance travelled to the ball and gravity. Extra speed can be generated by the double pendulum affect. Holding the wrist angle for a long as possible in the down swing increases stored energy by a concept referred to as lag. As the stored energy is released in the down swing at 30 degrees the club is released towards the ball greater speed is created. This results in a greater force being applied to the ball.

Newton's second law of motion, the acceleration of an object is dependent upon both force and mass. Thus, if the colliding objects have unequal mass, they will have unequal accelerations as a result of the contact force that results during the collision.

Newton's laws of motion are naturally applied to collisions between the golf club and the golf ball. In this collision both ball and club experience forces that are equal in magnitude and opposite in direction.

The force experienced by the club head is equal to the force experienced by the golf ball.

The forces upon the ball and club head are equal, but accelerations are unequal due to the size of the two objects at the moment of contact or collision. In simple terms club head and ball experience equal forces, yet the ball experiences a greater acceleration due to its smaller mass.

Golfers are well aware of this and refer to it as the "Smash Factor". This relates to the amount of energy transferred from the club head to the golf ball. The more efficiently energy is transferred the greater the acceleration. Smash Factor is ball speed divided by club speed.

The higher the smash factor the better the energy transfer. A golf swing of 100mph and a smash factor of 1.5 would create a ball speed of 150 mph. This can be affected by a number of other elements such as club lift and grip size, but ultimately the greater the club head speed the greater the Smash Factor and the further the ball travels. Hence for the same 100 mph club, a ball speed of 10mph speed difference will affect ball distance. A 10 mph in ball speed equates to a 20-yard increase in distance hitting a driver.

The upshot of Newton's laws of motion and the golf swing are simple. The greater the force applied to the smaller golf ball by the bigger golf club, the greater the acceleration, and the further a ball will travel. The acceleration of the club is produced by two pendulums working in concert i.e. the shoulder element and the wrist element.

## **6. Biomechanics of the leading wrist**

The leading wrist is placed on the upper golf grip and the trailing wrist on the lower element. Both hands are joined together by either interlocking or overlapping the index finger of the leading and small fifth finger of the trailing hand.

**Figure 2.** *Directions of leading wrist motion during a golf swing.*

*Leading Wrist Injuries in a Golfing Population. Golf Swing Biomechanics a Significant Cause… DOI: http://dx.doi.org/10.5772/intechopen.96979*

**Figure 3.**

*Classic left-hand grip showing less than one and a half knuckles (left) and a strong left-hand grip showing 3 or more knuckles (right).*

The leading wrist is placed in different anatomical positions to achieve a consistent contact on the golf ball. Each phase of the golf swing puts specific stresses and strains on the leading wrist and hand, which can result in different types of injuries [16–18].

There are 3 basic wrist motions during the golf swing. They are subtle and subject to significant variation [19] of motions from player to player (**Figure 2**).


At address the leading wrist is positioned in an ulnar deviated flexed position. It is pronated in strong grips (showing 3 or more knuckles), supinated in weak grips (showing one or less knuckles), (**Figure 3**) Classical teaching advises a neutral grip showing 1.5 or 2 knuckles.

In the back swing the leading wrist travels into a radial deviated, flexed and pronated position.

In the down swing the leading wrist travels into an ulnar deviated, supinated and extended position.

#### **7. Leading wrist ulnar/radial deviation in the golf swing**

At address, the leading wrist is usually held in ulnar deviation of the order of 17%. During the backswing, the left wrist transitions to a radial deviated position and then travels back to the ball transitioning again from radial to a predominant ulnar deviated position at impact (**Figure 4**).

Modern golf coaches often teach their pupils to hold the wrist in a radial deviated position for as long as possible on the down swing. This is referred to as a cocked position (**Figure 5**). When held in this position stored energy is increased. This cocked or radial deviated wrist position is created by maintaining an angle between the shaft and the left forearm in the downswing. The longer the wrists can maintain this angle, the greater the lag and resulting stored energy. This referred to "lag" as the club head is lagging behind the shaft caused by the wrist position, which is called wrist torque by golf teachers (**Figure 6**).

This manoeuvre is based on research which has shown that greater club head speed is achieved if an active wrist torque is applied to the club during the latter

**Figure 4.** *Leading wrist ulnar deviation at address and impact (right) and radial deviation at the top of the back swing (left).*

#### **Figure 5.**

*The angle between the shoulder, wrist and club head is maintained close to a right angle in the down swing to 30 degrees below the horizontal line through the shoulder joint, at which point the hands are released.*

#### **Figure 6.**

*The leading wrist in a flexed and radial deviated position maintains the angle between club shaft and arm to the bottom of the down swing, resulting in the head of the club "lagging" behind the hands storing energy.*

*Leading Wrist Injuries in a Golfing Population. Golf Swing Biomechanics a Significant Cause… DOI: http://dx.doi.org/10.5772/intechopen.96979*

stages of the downswing [19]. To produce a club head speed of 100 miles per hour, the optimal timing of the activation of wrist torque occurs when the arm segment is at approximately 30° below the horizontal line through the shoulder joint [20].

Therefore, significant timing of the shot is required to manoeuvre in releasing club head back square to the ball. This requires a careful return of the leading wrist from radial to ulnar deviation prior to impact.
