Biomechanics of the Golf Swing
By Glen Bowen
Reader Notice: The following information describing the ‘ideal proper’ golf swing is based on my understanding of biomechanics, the laws of physics, and my personal golf instruction experience as a certified professional golf coach.
I’ll state this early in my article,
The secret to a great golf swing is based on proximal-to-distal sequencing.
There are four sequences in the golf swing beginning with the Takeaway, followed by the Transition, then the Downswing, and ending with the Follow Through.
It sounds complex, and well, it is. But as you begin to understand how the sequence works in the golf swing and the consequences of performing this sequence correctly you will most certainly improve your chances of becoming a better player.
Golf is a stick and ball game. Sounds simple. But golf is one of the most complex sports on the planet. Without proper instruction about how to properly hit the ball with a stick, frustration almost always sets in early for those new to the game.
I’m frequently amazed to hear amateurs who’ve played for some years advise friends new to the game that all they must do to learn to play golf is to play. There is not an ounce of truth in this idea. As a result, their friends will struggle, become frustrated, and often give up.
The crux of the problem in learning to play golf without proper instruction and understanding is the use of the hands. We do most everything with the hands, so why not in golf?
Most inexperienced and many experienced golfers attempt to swing the golf club with their hands. It is a common error, or in the vernacular of golf teachers, a swing flaw.
And why not swing with the hands, after all, it is the hands that are in direct contact with the golf club—not other parts of the body?
For one thing, the hands contain the smallest muscles in the body. The arms have muscles smaller than most other parts of the body that involve the golf swing. Because of this, these muscles aren’t strong enough to swing the club fast with control.
When a golfer swings the club with their hands, the hands lead the golf swing. They tend to lift, or snatch, the club in the takeaway. This leads to multiple swing flaws including the most common one, which is taking the club inside too soon where it ends up behind the golfer.
When the club is behind the golfer the most common way back is by lifting the club over the trailing shoulder. This leads to and over the top swing with the clubhead crossing over the target line. The golfer then must swing back inside to contact the ball. This often results in a slice or a pull.
The dreaded slice is the most common swing flaw in golf because most players don’t understand the biomechanics of the golf swing.
In my golf instruction experience, most new students complain that they are inconsistent in hitting the ball. They can’t explain it because sometimes they hit shots that just fly off the club exactly the way they expect and at other times it seems they have trouble just making contact with the ball.
Golf tips and advice are literally everywhere and most of them are incorrect. This is because some golfers learned with a great amount of effort over time to compensate for their various swing flaws. Because this finally works for them, they have the mistaken idea it will work for their playing partners, or friends who are experiencing similar struggles that they did.
Proper golf instruction is one of the primary differences between an elite player and a rank amateur. Those new to golf often hear, “Practice, practice, practice makes you a better golfer.” This is certainly true, but only if combined with proper instruction. Without proper instructions these new golfers will likely ingrain lots of swing flaws because of their lack of understanding of the biomechanics of the golf swing.
The laws of physics describe every known physical property and action, at least on this planet where we live, work, and play. In the world of golf, it is critical to understand these laws when attempting to perform or describe the proper swing.
Velocity and Speed
Velocity and Speed do not have the same meaning and are not interchangeable, particularly as they apply to the golf swing. Velocity relates to speed in linear motion, but not in angular momentum which is the basics of the golf swing.
Newton’s Laws of Motion
Law of Inertia
The Law of Inertia states that an object will remain at rest or continue to move with constant velocity unless acted upon by an external force.
Therefore, we can state that in the game of golf the ball will remain stationary unless struck by a club. A ball struck by a driver will have a specific horizontal velocity at takeoff. The ball continues moving at a given speed endlessly unless an external force such as friction with the air slows it down after which it gradually falls to the ground and eventually stops rolling because of the friction between the ball and ground.
Gravity has no direct effect on the horizontal velocity of the ball, however just like every other object on Earth, gravity pulls physical stuff to its core and it certainly has an impact on ball flight.
Law of Acceleration
The Law of Acceleration defines the relationship between force, mass, and acceleration. Force equals mass times acceleration.
This explains why a golf ball accelerates faster from the big 460cc driver than for a hybrid club, or a 3-wood. The ball maintains the same mass, while the two clubs mentioned have vastly different masses. Because acceleration is the change in speed over time and relates to the mass of the striking club it’s easy to understand this dynamic. Again, mass makes the difference. Bigger is better.
Law of Action Reaction
Law of Action Reaction states that for every action there is an equal and opposite reaction. Forces work in pairs. For example, when we push something, it pushes back with an equal force. If you push against a wall you will fall to the ground unless your feet are pushing into the floor or ground with equal force. That’s easy on carpet but it’s much harder on a wet, slipperly floor. Imagine for a moment that you try to swing a golf club on an icy pond. You will immediately fall to the ice because there is near zero friction for your feet to push against. You will slip and fall, and hopefully not through the ice.
It is a little more difficult to understand and follow the sequence of the golf swing in terms of the Law of Action Reaction and biomechanics. The following is simple to state, but not easily understood.
During the downswing the golfer’s pelvis accelerates rotationally first, but when the upper torso accelerates a fraction of a second later the pelvis begins to decelerate. In the next sequence of the downswing the torso starts to decelerate as the shoulders, arms and hands accelerate. These also begin to decelerate as the club accelerates.
This is the reason why proper sequencing of the downswing provides the maximum power and increased acceleration. With each segment handing off to the next in the proper sequence the ball will be hit more efficiently and its distance will be significantly greater than swinging with the hands. If any swing element of this sequence is out of place the swing will lose its maximum angular momentum and consequently power and speed.
The gist of this sequence in the downswing is handing off power, or force, from one body segment to the next with increased acceleration with each handoff. This is the reason the golfer cannot swing the club as fast if he or she just using his or her hands to swing the club.
Center of Gravity
In the address position the golfer’s center of gravity is lower than when standing straight upright. If the golfer moves the center of gravity outside the player’s base of support [outside the feet], then the player will begin to fall. The golfer’s center of gravity does move during the swing while the body is rotating, swaying, thrusting, and lifting, and the arms and club are swinging. This is partly true because the swing is typically less than one and a half seconds in duration and the balance of the player’s weight remains inside the feet.
Force
A force is either a push or a pull. It is also a vector, meaning it has magnitude and direction. Pushing an object will cause it to move in the direction of the push. The greater the force in pushing the object the faster it will move. Also, force applies to and object at rest and that stays at rest until a force causes it to move. And in addition, a force such as friction is required to slow down an object that is already in motion.
Force can also be internal or external. In golf an internal force is created by muscles interacting with tendons, bones, and ligaments surrounding a joint. This is what causes body motion. In golf, the faster the motion, the faster the swing. This is termed inertial force and it relates to the how it is applied to the torso, legs, and arms.
An example of external force is gravity. Because of gravity’s force we are grounded when we address the ball. The better the address position, the more effective the use of gravity. The more skillful a golfer is in the swing the more that gravity plays a role in hitting the target. The improper rotation or sequencing of the golf swing will lead to negative effects of the golf swing because gravity will magnify the effects of the swing flaws.
Torque
In golf, torque is a combination of forces acting together in opposite directions. Therefore, it is important to rotate the shoulders fully while resisting with the hips in the backswing. The muscles become torqued based on this ratio. The more the hips rotate along with the shoulder rotation the less torque the muscles will possess and the less force they will have in the downswing. This loss of power will result in a less effective ball flight, particularly as it applies to distance.
Energy
There is potential energy at setup when you hold a golf ball in your hand, and is related to the mass of the ball, the height above the ground and gravity. However, the club and the ball are not moving so they have no kinetic energy, and the ball is not deformed so it also has no elastic potential energy.
Once the club drops from the top of the swing it gains speed and the potential energy is converted to kinetic energy. At the moment of impact, the ball deforms. Kinetic energy is then converted into elastic energy and the ball rebounds, converting the elastic energy back into kinetic energy.
Linear Momentum
Momentum is the “quantity” of motion that a body possesses. It is the product of the body’s inertia and velocity. This means that linear momentum is the product of mass and linear velocity.
Linear momentum can be transferred from one object to another while its energy is conserved. Just before impact the ball has no momentum because it has zero velocity. At impact, a ratio called Smash Factor comes into play.
Smash Factor
The smoother the golf swing flows from one swing element to the next in the proper sequence the more effective and efficient will be the transfer of power from the clubhead to the ball. Smash Factor is the qualitative measure of this transfer. Smash Factor is the ratio between swing speed and ball speed. The typical better player will register an excellent ratio in Smash Factor because the transfer of power has become grooved so well that the player usually strikes the ball in the club’s sweet spot squared to the target line. An example of excellent ratio is 1.35 for irons and 1.50 for drivers. Accordingly, if the player’s swing speed is 100 miles per hour, then the ball speed will be either 135 miles per hour, or 150 miles per hour based on these ratios.
Angular Momentum
Angular momentum is similar in principle to linear momentum but in a rotational sense. Angular momentum is proportional to the angular velocity and the rotational inertia of the object. The rotational inertial of a body is also known as the moment of inertia, but unlike linear inertia (i.e., mass), it is not constant.
Angular momentum is dependent on mass, angular velocity, and the distance of each mass element away from the axis of rotation squared. The squared part means that the distance of the mass from the center greatly affects the angular momentum.
A novice golfer casts the club from the top and the moment of inertia increases and the resistance to rotation increases so this novice golfer can’t swing very fast. In contrast, a skilled player, will cock their wrist in the backswing and maintain it until late in the downswing meaning that the club is close to the body for much of the downswing, keeping the moment of inertia low and allowing the golfer to rapidly increase the turning speed, which allows for a more rapid club speed when the wrist angle is rapidly released.
Ground Reaction Forces
Ground Reaction Force plays a smaller role in the backswing than in the downswing. The skilled golfer initiates the takeaway and continues the backswing by pivoting the shoulders while the hips resist. It is the resistance of the hips where the Ground Reaction Force comes into play. Because the golfer’s feet are in contact with the ground, he can perform this resistance.
However, during the downswing the Ground Reaction Force and Gravity plays a greater role because the skilled golfer will semi-squat and pivot forward to start the downswing. After the hips have pivoted forward past the ball, the skilled golfer will then push hard against the ground to lift himself back up just before impact with the ball, thus maximizing his power and speed.
In the golf swing, linear body motion is mostly side-to-side. There is some forward backward motion toward and away from the ball, but in a skilled player’s swing this will be minimal compared to the side-to-side motion.
In the backswing, the player moves slightly away from the target, putting more weight on the trailing leg. In the downswing as well as in the follow through the golfer moves toward the target and onto the lead leg. Shear Forces and Weight Shift create this motion. Shear Forces are forces parallel to the ground (horizontal forces).
These forces can be exerted due to the presence of friction. Therefore, good golf shoes are important. They produce the correct amount of friction to allow golfers to move appropriately. If the golfer is right-handed, he or she pushes to the left during the downswing with the trailing foot to move his or her body to the left.
However, the golf swing is mostly rotational, so in addition to the side-to-side forces the golfer must generate rotational forces on the ground.
Skillful golfers combine both the side-to-side and the forward-back forces on the ground to produce a fluid weight shift to the trail leg then to the lead leg with a simultaneous backward turn to a forward turn.
The Kinematic Sequence
In the golf swing the golfer’s muscles convert stored elastic and chemical energy into muscular force which allows him or her to generate a well-timed golf swing. An efficient swing requires the golfer to convert or transfer these various types of energy into motion. An efficient swing requires that each muscle fire and generate force with precise timing to generate and transfer energy to each subsequent body segment in the chain.
The energy starts from the ground up. The stronger, larger muscles of the legs and core accelerate themselves and the segments above them by pushing on the ground, then in sequence the smaller, fast muscles of the shoulders, arms, and wrists fire next to propel the club at maximum speed into the ball. This is known as proximal-to-distal sequencing, or kinematic sequence. It is a basic principle of human motion when the goal is to speed up a distal segment such as the foot, hand, or club.
In golf where the need is to create maximal speed of the club, there is a precisely timed sequence of body segment motions progressing from the proximal (inner), large segments to the distal (outer), smaller segments. During the downswing all body segments must accelerate and decelerate in the correct sequence with precise and specific timing so that the club arrives at impact accurately and with maximum speed.
The most efficient sequence of motion for the major segments is pelvis, thorax (upper body), arms, and finally the club. This motion must occur sequentially with each peak speed being faster but later than the previous one. This sequence reflects an efficient transfer of energy across each joint and facilitates an increase in energy from the proximal segment to the distal one. The muscles of each joint produce this increase in energy. On the other hand, if the timing of energy transfer is wrong, energy can be lost and hence speed will be lost. Also, if one body part must compensate because another is not acting correctly then injury may result.
During the downswing, the larger, inner segments such as the pelvis and thorax move slower with the speed building as the energy progresses to the smaller distal segments such as the arms and club. Note that the pelvis does not continue accelerating through impact but decelerates before impact.
Important Features of the Kinematic Sequence
The Takeaway Sequence
It is common for most unskilled golfers to begin their takeaway sequence with the club first through use of their hands, followed by their arms, shoulders, chest and then hips. In other words, they fail to initiate the takeaway sequence with their upper body starting with the shoulder pivot. This is a common mistake among untrained and new golfers. This swing flaw is also known as ‘reaching across the chest’.
The takeaway must always be initiated by the shoulders pivoting around the spine followed by resisting at the hips to create torque in the muscles. Not only this, but the club should be kept in front of the chest during the backswing, so the club doesn’t end up behind the golfer which is the number cause of the dreadful slice.
Transition Sequence
The transition is the point where the club stops moving in a backward motion at the top of the swing and before the downswing is initiated. This transition is followed by the downswing sequence. The primary focus of the transition sequence is to set up the transition from backswing to downswing to maximize the speed into the impact zone where the ball is to be struck with force. This force, of course, is clubhead speed.
It is during the transition sequence that torqued muscle power is stored and is waiting to be unleashed during the downswing.
Downswing Sequence
The downswing sequence consists of the hips being pushed by the trailing foot forward shifting the golfer’s weight to the lead side. This is followed by chest or thorax, then the shoulders, and penultimately the lead arm gripping the club, and lastly the club. The faster this sequence motion occurs, the greater distance the ball will travel through the efficient transfer of power known in golf as Smash Factor.
The sequence is often not followed by unskilled golfers because they are not trained to avoid the tendency of performing this task with their hands. This is the reason an untrained golfer will most often lead with their hands in both the backswing and the downswing which in both are swing flaws themselves. This produces slower swing speeds and consequently slower ball speeds. It is also the greatest reason for inconsistent ball striking. The hands should remain mostly quiet during the swing to prevent over manipulation of the golf club.
Accelerations and Decelerations – Acceleration is how fast each segment speeds up and deceleration is how fast each segment slows down. The key to a powerful swing is fast, sequential rotational accelerations and decelerations. The only thing that accelerates all the way to impact is the club. This is a critical feature of the downswing kinematic sequence.
Peak Rotational Speeds and Speed Gains – Each segment’s speed peaks sequentially and faster than the previous segment. The higher the peak speed of each segment the higher the potential speed of the club at impact. Also, the speed gain or increase from segment to segment, across each joint, is indicative of how much energy that joint contributes to the final speed of the club. If one joint speed gain is found to be lacking, then that may be an indication of weakness in that muscle group.
Follow Through Sequence
After the ball has left the club face the golfer must now slow the club down to a stop while still maintaining balance and avoiding injury. The arms should be fully extended in the through swing and allowed to rotate over each other so that the club can end up behind the golfer or wrapped around the golfer’s neck as seen in many skilled golfers. The club motion should basically die in the final position rather than banging the back of the golfer. With excellent balance, the golfer can hold this stance while watching his ball flight.
This is the secret to a proper golf swing.
—End
Submitted November 9, 2023, Glen Bowen, Certified Professional Golf Coach, US Golf Teachers Federation