Biomechanics is the scientific study of the forces acting upon and within a biological structure and the effects produced by these forces. Biomechanics addresses several different areas of human, animal and even plant movement. For example biomechanical studies have looked at how a plant turns itself towards the sun. Biomechanics includes studies on the mechanical functioning of muscles, tendons, ligaments, cartilage and bone by looking at their tensile strength, line of action and moment arms. The load and overload and the factors influencing performance of these structures are also researched.
Biomechanics of the golf swing applies the principles of mechanics to the structure and function of the golfer in an effort to improve golf technique and performance. The mechanical principles required for the golf swing include:
- Newtons laws of motion (inertia, acceleration, action reaction)
- Lever projectiles
- kinetic link principles
- stretch-shorten cycle of muscle, tendon and ligament.
Biomechanics provides analysis of the golf swing by measuring body angles, joint forces, ground forces and muscle activity patterns. This information helps golf professionals and coaches better understand the forces and muscles required to maximize the distance and accuracy of the golf swing. It also assists practitioners help reduce the risk of golf injuries.
To begin the biomechanical description of the golf swing is to maintain a single fixed center or the core which rotation occurs about, with two one-hinge levers as the moment arm or arms, to impart force on the ball. Measurement of the spinal angles are also collected to determine angular momentum using the kinetic link principle to generate high-club velocity – newtons law of acceleration linear and angular.
Biomechanical studies also measure ground reaction forces with a force plate. Research has shown that large ground reaction forces (GRF) are required to maximize the distance of drives. GRF are the forces that you push down into the ground with the feet – newtons law of action reaction. Studies have shown that during the back swing a greater proportion of the GRF will be observed on the back foot, and transfer to the front foot during the downswing/acceleration phase. At impact 70-75% of the body weight transfers from the non-target foot to the target side foot.
This weight transfer, swing of the two levers (arms) and rotation about a stable center (core) causes during the back swing rapid stretching of the hip, trunk and upper limb muscles, maximizing hip acceleration (X-factor) and uncocking of the wrists when the lead arm is at about 30 degrees below the horizontal. This stretch-shortening muscle cycle working along the kinetic chain of the body follows the summation of force principle – with all the links firing in proper order with maximum acceleration – generates large angular velocity of the club head, and ultimately ball displacement.
A biomechanical study was done on a Japanese golfer Hidemichi Tanaka. Researchers wanted to know how he generated so much club head velocity despite his small stature. Measuring ground reaction forces with a force plate and muscle activity with EMG the study showed, for this right handed golfer, that the muscles of his back leg initiated his down swing, before the upper body reached the top of the swing. During he back swing there was little minimal muscle contraction of the upper body until the left arm reached the horizontal level, and the ground reaction forces peaked with ball impact reaching 184 percent of body weight.
After impact forces then travel up the legs, thighs and hips to the lower back and beyond. If you hit a 5 iron about 150 meters, you generate about 160 kph (100 mph) club head speed, and to do that about 4 horsepower is required, to generate 4 hp you need about 16 kilograms of muscle. The best place to recruit 16 kilo of muscle is with the hips/thighs, large truck rotators and the core these are the powerhouse of the swing.
Physical conditioning will help recruit the muscles in the correct sequence and to optimum effect. Training the proper muscle firing to cause weight through the back leg, activation of the glutes and left internal oblique/external oblique for rotation.
Another biomechanical study from Stanford University School of Medicine conducted by J. Rose PhD, associate professor of orthopedic surgery, identified several factors that were consistent among professional golfers, published in the Journal of Applied Biomechanics. For the first time in a study several key rotational biomechanic elements of the entire golf stroke, from back swing to follow-through, were analyzed. A set of biomechanical factors were selected to capture the essential elements of power generation, as well as, to generate benchmark curves. They found the the swing mechanics were highly consistent among a group of professional players and at certain phases of their swings, their movements were almost indistinguishable from one another.
The results of this study can be used to improve golfer’s ability to hit the ball farther and do so without increasing their risks of injury. The authors indicated that previous studies already showed that the improper swing biomechanics is the leading cause of golf-related injuries. Previous studies also showed that 26-52 % of golf-related complaints involve lower-back injuries, 6-10% involve shoulder injuries and 13-36 % involves wrist injuries. “Over-rotation is one of the leading causes of back injury” J. Rose PhD.
The study by J. Rose et. al. was conducted in a gait and motion analysis lab where eight digital camera collected three dimensional motion images of the golf swings of 10 professional and five amateur players. Several biomechanical elements of the golf swings, including the X-factor – the relative rotation of the hips to the shoulders, measured in degrees. This is considered the key to power generation, as shown in previous studies that pro golfers who hit the ball far have larger peak X-factor than their peers. This study went a few steps farther by analyzing the X-factor in relation to other rotational biomechanics of the golf swing over the full duration of the motion from back swing to follow-through.
It found that the peak free moment, X-factor and X-factor stretch “are highly consistent, highly correlated to club head speed at impact, and appear essential to golf swing power generation among professional golfers.” J.Rose et. al. Additionally, they found biomechanical differences between pros and amateurs. For example the peak free moment of novice #1 was reduced and delayed compared with the professional, as “his X-factor was excessive in early back swing, but insufficient in downswing compared with professionals. Novice #2 had a reduced X-factor throughout back swing and downswing. “Both of these players had lower club speeds at impact than the pros did.
In summary the power generation in the golf swing is the result of proper kinematic sequencing to generate a high X-factor: the smooth coordinated rapid acceleration and deceleration at the pelvis, torso, shoulders/arms, and club head. “A precise understanding of the optimal rotational biomechanics during the golf swing may guide swing modifications to help prevent or aid in the treatment of injury, “ J. Rose et. al.
The reason why golfers may still have difficulty performing even after working with a golf pro is likely due to physical limitations, including movement or lack of range of motion and specific strength of muscles important in the golf swing. Physical conditioning will not only help the proper muscle firing patterns it will help restore adequate range of motion to help reduce risk of injury. Many physical limitations that predispose the golfer to injury manifest themselves at the ends of the golfer’s available movement (range of motion), for example at the top of the back swing.
For example as mentioned above the highest incidence of golf injury occurs in the lower back. Many golfers complain of low back pain occurring immediately after impact on the non-target side. Just after impact the body continues to rotate toward the target and at finish the spine should be erect, the pelvis and shoulders level and perpendicular to the target line and most of the weight on the outside of the target-side foot. During this follow through the spine should maintains a neutral position while, for a right handed golfer, the thoracic and lumbar spines must side bend to the right while they also rotate in the opposite direction, to the left.
If however, the spine side-bends and extends excessively in what is called the reverse “C”finish the vertebrae in the low back will be subjected to compression during loaded rotation, especially on the facet joints. This combination of rotation and side-bending forces is known as the “crunch factor” and reaches it’s peak just after impact. The reverse pivot or “C” finish is one of the most stressful to the low back causing, destructive shear (tearing) and rotational loads, the leading cause of low back pain in golfers.
This resulting combination of forces or crunch factor is actually the bodies own compensation for: 1) poor spinal flexibility and 2) the inability to maintain a stable pelvic base due to poor core strength of the lumbo-pelvic girdle. These two things spinal flexibility and core strength of the lumbopelvic girdle are key factors which Pilates training focuses on and improves. Pilates training not only reduces injury it improves golf stroke mechanics or sequencing, improves your X-factor stretch, and ultimately club head speed making your drive go farther.
A simple explanation of where rotation must occur in the body is in order to better understand kinematic sequencing and the x-factor stretch in the golfer. The human spine has vertebrae stacked one on top of the other resulting in inward curves at the lower back (lumbar) and neck (cervical). The mid-back (thoracic spine) curves slightly outward. Spongy liquid filled discs (intervertebral discs) are located between each of the vertebrae which distribute and decrease the forces on the spine. Posture during motion has significant effects on the forces exerted on these discs. The greatest loads on the discs occur when the spine is in a flexed, loaded, and rotated position – like just after impact in the golf swing.
The facet joints are how the spinal processes articulate with each other above and below each spinal segment or vertebrae. The direction of the facet joints must be considered during rotational movements. In the lumbar spine (low back) facet joints allow only forward and backward bending. Most rotation of the spine occurs (and should occur) in the thoracic or mid-back region where the facet joints are more horizontal.
The other place where rotation must occur during the golf swing is through the hip joints. For example the right hip (for right handed golfer) at the top of the back swing moves backwards or externally rotates about 45 degrees, while the left shoulder should be directly under the chin, with about 75% of the body weight should be on the inside of the right foot. This places significant rotational stress on the spine as the cervical and thoracic spine rotate toward the target to keep the head over the ball, while the shoulders, mid-thoracic and lumbar spine rotate away from the target. Restrictions in cervical and thoracic spine or hip flexibility will result in swing faults as the body attempts to compensate for those movement limitations. This also results in decreased pelvic velocity on the kinematic sequence graphs.
So achieving sufficient segmental spine rotation and external hip rotation is important at the top of the back swing to set up this difference in the amount of rotation between the shoulders and the hips. Jim McLean coined this difference as the “x-factor”. The differential gap between the shoulders and hips set up the next phase, the ‘stretch’. The “x-factor stretch’ that occurs early in the downswing is responsible for generating power in the golf swing because in pre-loads the muscles in the torso and pelvis, much like stretching a slingshot before letting it fly.
Often golfers rotate the spine past its natural limits to increase this differential between the shoulders and the hips, however, this can result in injury by overloading the soft tissue. Additionally, it can cause excessive rotation of the lumbar spine, when rotation is suppose to occur mainly in the thoracic spine.
Pilates for Golf
Often the thoracic vertebrae become stiff and lose their ability to rotate, where the lumbar spine often losses it’s ability to extend. Hips often become very stiff with tight hip flexors and hamstrings the hip losses it’s natural range of motion. Pilates helps improve these motions of the spine and hip plus specifically builds the muscles which assist and maintain these motions. The athletic golf swing is all about posture. Being able to maintain proper or good posture means good mechanics in motion – and good posture equals power. Good posture throughout motion means the body segments are in the proper, most biomechanically efficient position, with minimal stress or shear forces on the body parts, so that proper sequencing can occur in order to increase club head speed.
Balance is an important element of a golfer, as a golf swing requires the body to perform simultaneous rotational and linear movements, in the correct sequence and with the correct timing. Balance requires two physical components of your body to work together, your muscles and nerves. These systems working together allow for postural alignments, center of gravities, weight transfer and spine angles to be maintained during all phases of the swing, not just at the address stage. Improving posture and balance is one way to build a repeatable swing and consistent swing path.
Balance is particularly important in the transition, the point where the backswing in completed and the downswing is initiated. This phase of the swing requires high levels of rotational flexibility and it requires acute levels of balance. As the golfer must both maintain balance of the body as a unit and the control the extremities (arms and legs). It is the integration of the body and swing mechanics (club, arms, legs) that allows the golfer to “stay balanced” during all phases of the swing. In order for the transition phase to be performed efficiently and effectively the golfer must be able to maintain balance in the a rotational pattern or coil. The coil is where the lower body initiates forward movement and the upper body continues a rotation backwards. Better control of this coil is achieved with exercises which train both the nervous and muscular systems to become more efficient in rotational movement patterns. Again, the Pilates method focuses on these types of exercises which develop cross connection strength between the right upper body to lower left and visa verso.
The final discussion of balance is during the address, the position the golfer places their feet and the rest of the body. Biomechanic studies have shown that by placing weight in the mid section of the foot – the arch and heel region of the inner foot – you allow maximum rotation through the pelvis, plus the natural inclination to lean forward through the backswing is countered with this stance. This can be readily demonstrated; try placing all of your weight on the outer aspect of your feet and see how difficult it is to rotate. Then try placing your weight on the inner aspect of the foot, it is much easier to rotate. This is because the tibia and fibula rotate medially allowing the femur to rotate laterally placing the hip in a more neutral position. Pilates training on the reformer draws particular attention to how the line of gravity acts through the foot ankle, knee, hips and pelvis, greatly improving your overall balance and ability to “organize” or position the body.
Often when a golfer begins Pilates training their golf scores become worse or their game looks like it is getting worse. However, you must remember Pilates changes your body. It will increase your cervical and thoracic rotation and shoulder girdle flexibility allowing you greater back swing. It will increase lumbar extension motion and strength. It will increase core strength providing stability of the lumbo-pelvic girdle and better over all balance. Pilates will develop greater ease of movement. With greater range of motion, balance and strength, new timing and muscle sequencing patterns will need to be developed. Working with your local golf pro will pull together your new body and swing mechanics.
Synthesis of Swing Mechanics and Body (muscle performance) to create Power:
Two factors contribute to the creation of power in a golf swing. The first is the swing mechanics or how the golfer sequences the body. The second is the body and the ability of the muscles used in the swing to create power. Pilates can help both build and balance your muscles so they work optimally and help your swing mechanics. It is the synthesis of these two components that create club head speed. Some of following has already been discussed, however the following presents how swing mechanics and the body integrate to generate club head speed, as indicated by biomechanical research of an ideal golf swing.
During the back swing is where the body stores energy to be released as clubhead speed. The transition phase is the point at which the energy stored by the body begins to be directed into the golf club in the form of clubhead speed (power) and where power can be measured. During the downswing this creation of power occurs in about 0.4 seconds. Between the top of the backswing and ball impact the body rotates to generate, accelerate and transfer velocity sequentially from the pelvis to the upper torso to the arms and finally the club face.
The hips and pelvis begin the motion as they initiate a change in direction and start to rotate forward, yet the shoulders continue to rotate backward during early downswing, this further increases the differential between the shoulders and the hips. This rapid counter-movement pre-loads the torso musculature, particularly the oblique abdominals to enhance the concentric torso rotation or angular acceleration. This kinetic sequencing starts from the ground up with ground resistance. A golfer shift-rotates his pelvis at the start of the downswing by pressing into the ground to torque his pelvis in a shift-rotational manner.
Shortly after that, the upper torso start rotating around a rightwards tilted spine. Some of the torque forces used to rotate the upper torso are passively transmitted from the lower torso to the upper torso via the spine and external torso muscles, but most of the torque forces are derived from the active muscle contraction of the mid-upper torso muscle. The combined rotation of the lower and upper torso represents the pivot action, and this pivot action essentially drives the swing and is responsible for the resulting power generation from the body and it’s muscles.
During the backswing, the left arm is pulled across the chest, and by the end of the backswing it is loaded against the upper torso. The left arm is inert in the modern, total body golf swing and it responds passively to movements of the upper torso during the downswing.
When the shoulders start rotating in the early downswing, the arms are pulled along at the same speed as the rotating upper torso. In other words, the left arm is powered by the rotating upper torso. At a certain time point in the swing (usually when the upper torso decelerates), the left arm is passively catapulted or blasted away from the chest wall and the left arm then freewheels towards impact. The energy used to propel the left arm towards impact is derived from the rotating upper torso, via the pivot-driven swing action.
An important feature of the golf swing is is that it is a continuum of related movements and not a series of static positions. A good golf swing is a smooth, free flowing motion that carries the body around to a full finish. Many think of just hitting the ball instead of hitting through an impact zone and the swing is has a jerky, abbreviated follow through. Professional golfers keep on rotating smoothly through the impact zone to a full finish.
Research has demonstrated that professional golfers hit through the impact zone (simply strike the ball on the way through) and the momentum generated during the downswing carries the body effortlessly forward to a complete follow through. The end follow through position has the right arm fully extended in the early-intermediate follow thru period, and the club finally goes over the top of the left shoulder to wrap behind the upper back. The right shoulder continues to move through (under the chin) and the shoulders turn fully to an endpoint where the right shoulder is closer to the target than the left. The body weight is transferred from right to the left side, standing upright over a straight left leg. If the golfer can hold the follow through for a few seconds it indicates proper balance.
That is a lot of analysis just for a seemingly simple athletic activity which takes less than a second to complete! The point of this article was to draw attention to the areas of the golf swing where restrictions or limits in range of motion can cause swing compensations and possible injury. I hope this has helped you think about your own swing mechanics and brought awareness to your body. Pilates is an immensely beneficial exercise method that can certainly help anyone’s golf swing and many other aspects of one’s life. Try Pilates you will feel the difference.
Adapted from Pilates for Golf. This article written by Samantha Reed who studied Physical and Health Education and Biomechanics at the University of Toronto. She is a fully certified Pilates instructor, a builder, avid snowboarder and outdoor enthusiast.