The Basics of golf 3D kinematics
Note:
This article is closely related to the golf ground mechanics article. If you have not read that article, I suggest reading it first. You can link to the ground mechanics article here.
Introduction
In the ground mechanics article, we established that the primary role of the legs in the golf swing is to create pelvic rotation. But what happens after that? Somehow the energy of pelvic rotation must now be transferred into the club and ultimately into the ball itself. The term “kinematics” refers to this transfer of energy throughout the upper body to the club. Kinematics are analyzed by using motion sensors that track the 3 dimensional movements of different body segments. The sensors can track the location of these segments in space, but perhaps more importantly, they can track the relative rotational velocities of each segment along with their individual acceleration/deceleration patterns.
There are many different systems out there, some with many sensors all over the body and there is a world of complex data that can be analyzed using 3D motion capture. The scope of this article is to present the basics in clear terms. Four motion sensors is a widely recognized standard to gain a sound understand of the basic kinematics of the golf swing and this is what is used at Iconic Motion. These sensors are attached to the following segments:
Pelvis
Chest
Lead Arm (The arm towards the target. Sensor placed at the upper arm.)
Club
By studying the acceleration and deceleration of each segment, we can follow the energy of the swing as it transfers from the pelvis out to the golf club.
Peak rotational Speed
It is important to make sure that the golfer can create speed in each segment. One of the first things to look at in a 3D analysis is the peak rotational velocity of each segment. This is the fastest recorded speed of each segment during the downswing. If any segment is slow it can give a clue as to where the golfer is losing speed and inform drills or exercise prescriptions.
As golfers, many of us are used to looking at club head speed measurements in the units of miles per hour. Motion capture speeds are expressed in degrees per second because they are measuring rotational speed, not linear speed.
Standards have been established for these peak speeds as follows:
Pelvis: 550 degrees per second.
Chest: 750 degrees per second.
Lead Arm: 1150 degrees per second.
Club: 2150 degrees per second.
segmental Speed gain
Speed numbers should increase in magnitude as you move from pelvis to club. In other words there is a summation of speed occurring as the swing happens. This is important because it represents an energy trace that can be followed from pelvis to club. Ideally, the chest moves faster than the pelvis, the lead arm faster than the chest, and the club fastest of all. If speed gains are below standard for any segment, this represents a speed leakage or inefficiency in the system that can be identified and addressed specifically.
Although it may seem like peak speeds and segmental speed gains are just the same thing expressed two different ways, they are not exactly the same. “Peak speeds” is measuring the raw speed of each body segment while “segmental speed gains” is measuring the efficiency of energy transfer between segments. For example it is possible to have segmental speed gains fall within ideal ranges (efficient) but for the individual peak speeds to still be slow. In fact, any of the following outcomes are possible:
1. Slow and inefficient.
2. Slow and efficient.
3. Fast and inefficient.
4. Fast and efficient.
Standards have been established for efficiency as follows:
Chest: 30% - 40% faster than the pelvis.
Lead Arm: 40% - 50% faster than the chest.
Club: 100% - 120% faster than the lead arm.
Sequencing
So far we have identified the ideal peak speeds of each body segment and described how the speed should be transferred between segments on the downswing. The next part of the kinematics analysis is to examine sequencing. There are 2 sequences in the golf swing that tend to matter most:
1. Transition sequence.
2. Downswing deceleration sequence.
Transition sequence
The transition sequence is the order in which each body segment changes its direction of rotation from backswing to downswing. The ideal transition sequence is pelvis, chest, lead arm, club. This creates a rapid stretch in each segment that harnesses the elastic energy of the muscles and connective tissues associated with that segment. When segments transition out of sequence, this elastic energy is lost. The transition sequence could be thought of as the acceleration phase of the downswing, beginning at the pelvis.
This means that for an ideal transition sequence:
The pelvis has already begun the downswing while the chest is still completing the backswing.
Core muscles between the pelvis and chest are stretched.
The chest has already begun the downswing while the lead arm is still completing the backswing.
Lead arm shoulder muscles between the chest/rib cage and upper arm are stretched.
The lead arm has already begun the downswing while the club is still completing the backswing.
Lead forearm/wrist muscles between the lead arm and the club are stretched.
downswing deceleration sequence
The downswing deceleration sequence is exactly what it sounds like: The order in which each body segment decelerates in the downswing. The ideal sequence is again: pelvis, chest, lead arm, club.
I realize that the word “decelerate” tends to be a bad word in golf instruction. Please consider this strictly from a biomechanical point of view. The ultimate goal is to create optimal club acceleration and speed. But to do this, certain body parts must also decelerate to transfer their energy to the next body segment.
To visualize this sequence, recall that the pelvis was the first body segment to make the transition from backswing to downswing. This means it was the first segment to accelerate in the downswing. As the pelvis continues to turn faster and faster we know from our segmental speed gains analysis that eventually this speed needs to transfer to the chest. The way this happens is the muscles of the core connecting the pelvis to the chest above it contract forcefully. This has a double effect: The chest rapidly accelerates while the pelvis decelerates. So while the pelvis was first to accelerate in the downswing, it is also the first to decelerate. This is how speed is transferred between segments. The firing of linking muscles accelerates one segment, but decelerates the segment immediately previous to it. This process repeats itself 3 times in the kinematic chain:
Between the pelvis and chest link
Between the chest and arm link
Between the arm and club link.
This also means that each segment is dependent on the segment before it in the chain for its speed. As the swing progresses it gets more and more difficult for upper body segments to make up speed for lower body segments that might have been slow in the first place. Poor lower body mechanics leads to upper body dominant golfers. This creates speed and consistency problems and may increase injury risk as the golfer is over reliant on one or two upper body segments for speed production.
In summary:
Poor ground mechanics ➜ slow pelvis ➜ slow chest ➜ slow lead arm ➜ slow club ➜ slow ball ➜ less distance ➜ sad golfers.
🏌🏽♀️🏌🏼♂️ = 😥
Examples
Let’s take a look at the kinematics of 2 actual golfer’s swings and see how 3D motion capture along with physical assessment can greatly inform our exercise prescription.
Golfer 1:
Handicap: Scratch
Driver Club Head Speed: 110 MPH
Peak Rotational Speeds:
Pelvis: 471° per second
Chest: 737° per second
Lead Arm: 1040° per second
Club: 2240° per second
Analysis and Body-Swing Diagnosis:
This golfer does a great job of creating speed in each segment with perhaps the exception of pelvic speed, but even 471 is a good number. Pelvis speed is created by the lower body and ground reaction forces. In this golfers physical assessment, one of the most notable findings was a severe lack of lower body strength and power. This means that with some lower body strength/power exercise, this golfer has potential to improve their pelvic speed. This could have a positive impact on club head speed without making any swing changes at all.
Segmental Speed Gains:
Chest Gain from Pelvis Speed: 56%
Arm Gain from Chest Speed: 41%
Club Gain from Arm Speed: 115%
Analysis and Body-Swing Diagnosis:
These are impressive speed gains. Efficiency is the primary reason this golfer can produce good club head speed. Each of these links is transferring energy nicely creating a balance among body segments. No single segment is working too hard and there is a summation of speed from pelvis to club.
Transition Sequence:
Pelvis | Arm | Chest | Club
Analysis and Body-Swing Diagnosis:
Arm and chest transitioning out of sequence can happen often, even with better players. Even though the two are flipped, the lower body (pelvis) is still transitioning first which is the most important part of the transition sequence. Any shoulder or spine mobility or pulling strength issue could contribute to this problem but neither were found to be a significant issue for this golfer. Therefore it is likely a motor control skill that needs some practicing. There are sequencing drills that focus specifically on the chest to arm link that could help this golfer harness even more speed.
Downswing deceleration Sequence:
Pelvis | Chest | Arm | Club
Analysis and Body-Swing Diagnosis:
Perfect sequence here. This golfer was able to pull this off on every swing captured during their evaluation. This is what leads to the excellent efficiency in energy transfer between segments.
Golfer 2:
Handicap: 20
Driver Club Head Speed: 68 MPH
Peak Rotational Speeds:
Pelvis: 487° per second
Chest: 623° per second
Lead Arm: 534° per second
Club: 1511° per second
Analysis and Body-Swing Diagnosis:
This golfer gets off to a good start with pelvic speed but as you can see, the speed begins to drop off at the chest and then severely decreases at the arm. In fact the lead arm is actually moving slower than the chest. Decreases in speed like this are characteristic of an upper body dominant move where the lead arm and wrists fire too early. Recall that when one segment fires, the segment immediately prior to it in the chain decelerates. In this case, the biggest issue is the wrists firing too early which causes a deceleration of the lead arm. This pattern of movement on the downswing is commonly known as “casting.”
Physically some wrist mobility and grip strength issues were identified that might make it difficult for this golfer to maintain wrist angles longer in the swing. Wrist mobility and grip strength activities were assigned. Wrist/club sequencing drills were also assigned. Another possible reason for this could be poorly fit equipment, specifically a club that is too heavy. This golfer has yet to be professionally fit for their driver.
Segmental Speed Gains:
Chest Gain from Pelvis Speed: 26%
Arm Gain from Chest Speed: -17%
Club Gain from Arm Speed: 183%
Analysis and Body-Swing Diagnosis:
These numbers again reflect the casting characteristic as the most notable issue. Something else to notice here is that the link between the arm and the club is doing a LOT of work. Gain between arm and club should be 100% - 120%. A gain of 183% is not simply better because it is a higher number. In fact, it reflects the imbalance between segments. It is no wonder that this golfer has struggled at times with elbow pain. Improving sequencing would significantly reduce risk of further elbow injury.
Transition Sequence:
Pelvis | Club | Lead Arm | Chest
Analysis and Body-Swing Diagnosis:
Although this golfer again does a nice job of transitioning the pelvis first, the club and lead arm transition next which is further evidence of an upper body dominant pattern of movement.
Downswing deceleration Sequence:
Lead Arm | Trunk | Pelvis | Club
Analysis and Body-Swing Diagnosis:
Lead arm decelerating first is again showing that the wrists are firing early. Trunk decelerating next shows the lead arm is firing early. This golfer had immediate success after working on some wrist/arm sequencing drills and after some time working on her wrist mobility and grip strength. Driver club head speed jumped up above 70 MPH in a very short amount of time.
speed vs. power
It is important to recognize that speed and power are not the same thing. The ability to hit the long ball is a question of power production. Kinematics analysis is looking at speed transfer only. Strength, speed and power are related but they are distinct properties of physical ability. Mathematically, power is the product of speed and strength.
Power = Strength x Speed
For example it is possible to have a junior golfer that can show impressive speeds in all body segments during a kinematic analysis, but they don’t hit the ball 300 yards because they have not developed sufficient strength. Golfers should look to develop power by first establishing a foundation of strength and then layer on the speed.
Conclusion
The analysis presented here is only one part of what is measured using 3D motion capture. The system creates a 3D avatar that can be viewed from any angle allowing you to examine such things as:
Spine Angles
Shoulder Plane
Pelvic Plane
Club Path
Hand Path
Upper Body/Lower Body Separation
Total Rotation
And MUCH more!
Such things are beyond the scope of this particular article but watch out for future articles that examine topics associated with some of these other tools.
To conclude this discussion, hopefully it is clear how a kinematics analysis would be useful. It allows a precision examination of speed transfer and efficiency that is simply not possible with a video analysis. Precision analysis informs exercise prescriptions that are highly targeted and individualized. Not every golfer is the same and there can be many different problems identified, each requiring a unique solution. This is why it is crucial that each golfer’s physical abilities and swing data be evaluated individually. There is simply no better way to understand your individual needs except to have a thorough evaluation.
If you are interested in discovering your potential for improvement and developing some custom programming to fit your needs, Iconic Motion is here to help. Schedule your free phone consultation or initial evaluation here to get started.