Too Much Back Turn

In an attempt to generate extra power, many players over-rotate in the backswing to maximize separation between the upper body and lower body. However, this level of backswing rotation comes at a cost: an inefficient transition from backswing to downswing, and loss of lower body stability are frequent problems that we see.

Here is a strong player with great flexibility who rotates the upper body (thoracic spine, including shoulders) more than 20 degrees greater than is typical for 2/3 of pro tour golfers (green numbers range in above figure). Pelvis rotation for our golfer remains within the range of 2/3 of tour players. 

The separation between upper body and lower body in this player (K-angle = 66 degrees) is more than needed for full efficient power. It can prevent initiating the downswing with the pelvis, a pre-requisite for maximum efficiency in the downswing -- in this evaluation, with a driver.

The consequences of over-rotation in the backswing can be seen in starting the transition with the upper body and a destabilization of the lower body in the downswing. The pelvis reaches its maximum acceleration somewhat late in the downswing making it difficult to transfer full power to the upper body in time for optimum swing efficiency. (The power transfer ratio is less than optimal.)

Biofeedback training that allows a golfer with these characteristics to feel the optimum range for backswing rotation is an effective starting point for improving driver results. Adjusting length, weight, swingweight, and shaft stiffness characterisitics can be incorporated into the strategy for game improvement. Understanding your swing mechanics matters when fitting for new clubs.

K-Vest TPI Reports

An effective approach to understanding a golfer's swing is by using digital 3D motion capture for an unbiased analysis of any swing detail. It removes the limitations that come from visual perspective errors and the difficulty of seeing subtle movements that are masked by the speed of the swing. 

Most golfers looking for help with their technique, an evaluation of their range-of-motion, or having clubs fit accurately to their swing benefit from portable 3D systems that are easy and quick to use. The K-Vest meets that requirement and collects data that allows direct comparison to TPI databases of pro swings, the most comprehensive and useful reference available for understanding swing mechanics.

Here is an example of the TPI version of the K-Vest software showing data from a player who is casting the club and swinging with a force that destabilizes his upper body and lower body through the downswing. Excessive forward bend of the pelvis in the downswing makes it difficult to control the path of the club and increases risk of lower back injury. 

The upper left panel shows the path of the club captured at 180 frames per second. The downswing is above the plane (over the top) of the backswing. Spacing between club shaft frames in the downswing is greater than the spacing of frames in the backswing as expected, and helps confirm the identity of the downswing plane. As the club frames approach impact, the downswing plane merges with the backswing plane. 

The kinematic sequence panel shows the downswing is dominated excessively by the force of the club from the top of the backswing through the early part of the downswing. The upper body and pelvis are not sufficiently stable to resist the force of the club and reach their full potential acceleration in the downswing. The pelvis slides through impact and is not efficiently transferring power to the upper body.

This separation between the club path and upper body acceleration graphs is characteristic of casting (early release), a problem that often accompanies over-the-top motion. The pelvis compensates by tucking in towards the target line in the last half of the downswing. It's characteristic of the early extension swing fault, the most common problem among amateur golfers and contributes to casting and over-the-top movement patterns.

These data are just a brief look at a highly detailed portfolio of graphs, tables, and images that can be analyzed to characterize any golfer's swing efficiency. It's the basis for knowing your swing and understanding how to build a strategy for game improvement and custom club fitting.

Update on Thursday, January 2, 2014 at 9:13 PM by John Taylor

The original blog post has been updated with a brief analysis of the motion capture data of the included figure.

Role of Angle of Attack

The angle that a clubhead's center of gravity (CoG) makes with the ground at impact is the angle of attack (AoA). Hitting up on the ball is a positive AoA. It's what you want with a driver. Hitting down on the ball is a negative AoA. It's what you want with an iron.

Here are measurements of the AoA for several iron swings as determined by our FlightScope radar launch monitor. This player has a relatively consistent downward AoA (yellow lines), typified by the swing shown in red with a negative AoA of -2.0. 

The performance of your clubs and the effectiveness of your swing is affected significantly by the AoA. Launch monitor measurements show that AoA contributes to ball spin indirectly according to its relationship with launch angle and club loft at impact. Empirical evidence finds that AoA accounts for about 15 % of the measured launch angle, with the balance determined by club loft -- more specifically, dynamic loft of the clubface at the point of impact.

The contribution of AoA to ball spin and launch angle is indirect. The difference between angle of attack and the dynamic club loft at impact effectively defines the "spin loft" at impact. It means that a positive angle of attack permits use of a lower lofted driver to maintain an optimal launch angle while reducing ball spin for maximum distance. Hitting down on the ball for a negative AoA has the opposite effects on launch and spin -- it's a distance killer.

Achieving a positive AoA with a driver is always desirable to maximize distance. Here are changes you can make to your swing through impact that will help generate a positive AoA:

Alignment -- open upper body favors negative AoA

Ball position -- forward position favors positive AoA

Posture -- upper body left tilt favors negative AoA

Weight balance -- more weight on left foot favors negative AoA

Club path -- swing to the right favors positive AoA

 

Kinematics and Speed

The key to speed in the golf swing is each body segment accelerating and decelerating in a precisely timed proximal-to-distal sequence. Analysis of thousands of swings from the professional golf tours reveals the most efficient swing sequence movement pattern is pelvis, thorax, arms, and club through the swing. For maximum speed, each segment must achieve a higher peak speed at a slightly later point in the sequence than the previous segment.

Optimizing the timing between segment transitions at the “top” of the backswing and between maximum peak speeds in the downswing is essential to achieving maximum speed. Too much or too little separation in time between the segments limits the power and speed that can be generated by power transfer across joints from one segment to the next. The analysis of PGA tour pro swings gives us ranges for timing and speeds attained at each point in the swing for comparisons and understanding swing efficiency.

Energy generated by the lower body pushing against the ground gets the pelvis turning in the transition from the top of the backswing to the downswing. Isometric contraction of core muscles allows potential energy to build between pelvis and thorax.

In the transition from backswing to downswing, “X-factor” concentric stretching allows for extra force to build up, and we see it reflected in the widening of the spine angle between pelvis and thorax at the start of the downswing. The X-factor stretch contributes directly to increasing speed. The dynamic loading from stretching between two segments is indicated by the calculated area between the acceleration curves for each segment.

The rate and extent of deceleration is facilitated by lower body stability pushing against the ground, and is important in allowing the thorax to achieve its maximum speed gain. Increased rate of thorax rotational speed depends on pelvis segment stability in this part of the golfer’s proximal to distal chain.

The same considerations apply up the chain of segments and joints through the arm and the wrist. Lack of stability can often be seen in a delay in the timing of the maximum peak speed and in the rates of both acceleration and deceleration. We see it as inflections or flat sections or decreased slope in a kinematic sequence curve.

Transition Sequence

The transition from the top of the backswing to the start of the downswing has a substantial influence on achieving maximum distance from your swing. Kinematic analysis shows the sequence and timing by which major body segments rotate and move through the transition have a major effect on efficient power generation in the downswing.

The optimum sequence order in the transition is pelvis, thorax (upper body), arms, and hands (club). The start of the transition sequence is when the first segment -- the pelvis in an efficient swing -- turns towards the target and the end is defined as when the club moves towards the target. The timing and sequence order between these transitions is a reliable indicator of efficient power transfer.

When the timing of the transition between individual segments is too long or too short, or when the sequence of the segment transitions is not in the optimum order, then some of the potential power that's been built up in the backswing is lost. The order and timing of body segment rotation in the transition is the firing sequence for initiating power production in the downswing.

The movement of body segments through the transition reflects changes in muscle tension. For example when the pelvis moves faster than the thorax in an efficient transition, the spine angle is widening due to stretching or eccentric contraction of core muscles. When the thorax transitions towards the downswing, concentric contraction releases stored energy. We can think of it as a stretch-shorten cycle.

The stretch-shorten muscle cycle in an efficient transition sequence is an extra source of power in the swing. It's been termed "X-factor stretch" by Phil Cheetham who initially quantified this effect in the kinematic sequence.

Optimizing effective power generation begins with our measurement of how your pelvis and thorax moves through the transition using 3D motion capture technology. Identifying what is limiting in your transition sequence provides a basis for corrective drills and exercises to promote an efficient swing.