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Stack'n'tilt as a therapy aid

Dave Tutelman -- September 3, 2023

I am healing from an injured gluteus maximus. I have found the stack'n'tilt swing seems to be an effective workaround, while I rehab with physical therapy. This swing causes minimal stress to the glute, is pretty easy to learn, and doesn't cost much in the way of performance -- perhaps a half-club to a club in distance and no other noticeable degradation. Here is the reasoning and the biomechanics.

The problem

I hurt my back playing golf in early July 2023. I thought it was a return of my sciatica, a compressed disc. Dr Michael Lospinuso, a really good back specialist who also plays golf, ruled that out quickly and concluded that I had torn my right glute. I guess doing an enthusiastic (and proper) hip turn can still be dangerous, at least if you're 82 years old. Per his prescription, I am rehabbing at JAG One Physical Therapy in Oakhurst, NJ, mostly with Mike Santamaria and sometimes Gianna Vassallo. In 2019, Mike and his team got me back on the golf course after sciatica sidelined me for the whole previous year, so I trust them.

The therapy, of course, is increasing the strength and flexibility of the injured right glute, and all related muscles. That includes symmetry (left glute), antagonists (abs and hip flexors), related and nearby muscles (hamstrings, quads), and just generally making my core strength more robust. After a month, I was very anxious to get back on the golf course. Mike was supportive of this, but I needed to "not overdo it". Mike is a golfer himself, and knows that "not overdo it" probably means walking off the course if it hurts. More to the point, it means walking off the golf course before I re-injure it and have to start over -- maybe from an even worse condition.

That's experience speaking, not just my imagination. When I first injured it, the pain forced me off the course on the 11^th hole. I rested it for a week, felt fine, but then just five holes of golf put me in worse pain -- and worse shape -- than when I walked off the week before. That's when I went to the doctor and wound up in physical therapy.

Even figuring out when therapy was over would require trying to play golf -- but not overdoing it. In order to tell whether I am healed and can be discharged from therapy, I have to go out and do repeated forceful contractions of my injured glute (called "golf swings") and stop when they begin to hurt. If I don't stop, I am likely to re-injure them and we're back to square one with the therapy. But once I am on the golf course and playing a round, I find it hard to stop, walk off the course, and go home. And not doing so is the very definition of "overdoing it".

A potential solution

Of course, one solution is to stop playing golf until I am healed. Unacceptable for a couple of reasons:

I have a want and a need to play golf. It is my exercise, to keep me physically fit. It is my entertainment, to keep me mentally healthy.
This injury is most apparent when aggravated by a golf swing. Playing golf is the recommended and most effective way to tell when I am healed, perhaps the only way.

But maybe there is a better way. Suppose there were a "safe" golf swing that allowed me to play golf, but only demands little to no effort from the trail glute? If there were, then I could play golf, but revert to the safe swing if and when I felt a twinge of gluteus maximum trouble. Instead of walking off, I could play the rest of the round with the safe swing.

The Stack and Tilt Golf Swing, known informally as stack'n'tilt or S&T, looks like it could be a safe swing. The essence of stack'n'tilt, the thing that sets it apart from other swing techniques, is that the weight stays on the lead leg the entire swing. If the goal is to avoid overworking the trail glute, it sounds promising. This way, I can try my full-weight-shift normal swing any time during a round, but I can finish the round with stack'n'tilt if I am feeling a little warning twinge.

The next chapter explores the biomechanics of the normal golf swing (the problem) and the biomechanics of stack'n'tilt (the potential solution). If you are not interested in the biomechanics, feel free to skip ahead to my experience using S&T as a safe swing.

Biomechanics

Here we look at the muscular actions that drive the golf swing, specifically the muscles of the lower body, the hips and legs. The upper body is also an interesting biomechanical study, but not relevant to the current question: how does the golf swing use the gluteus maximus on the trail side, and how can we minimize that use?

The golf swing plane is at an angle; it is not straight up and down, nor is it just "around". In what follows, I'll look separately first at the muscular actions that cause horizontal (top view) rotation and then at the actions that cause vertical (frontal view) rotation. This is not the way to do it for an accurate, detailed analysis, but it is easier to understand this way.

So, some of the approximations and simplifications in the analysis below:

Only the hips and legs will be considered.
The horizontal ("transverse plane") and vertical ("frontal plane") kinetics will be treated separately.
Most or all of the muscles will have some contibution, but I'll only discuss those that make a major contribution.
This is not a quantitative analysis! A professional biomechanical study would look very different. It would start with a motion capture system and continue with a full-body inverse dynamics analysis to determine the torques at each joint. That can be used (with some effort) to calculate the forces exerted by each muscle. Once again let me emphasize, we are not doing that. This is a very informal "analysis".

The normal golf swing

The way I would characterize the "normal golf swing" for purposes of this article is: on the backswing, the weight is loaded onto the trail leg (the right leg for a right-hander like me). On the downswing, that weight on the trail leg is used to push off and rotate the body, both horizontally and vertically. Let's look at the forces involved and which muscles they come from.

Horizontal forces

Let's start with the rotation of the lower body in the transverse plane -- the top view. (This picture and the next are adapted from a frame grab of a Brendan Steele video on the HackMotion web site.)

A power move in the golf swing is the hip turn. Let's take a look at what drives it, and what makes it a power move. During the first part (perhaps the first half) of the downswing, the dominant movement is hip rotation. The green arrows in the picture show that hip rotation comes from:

The trail (right) hip moving forward.
The lead (left) hip moving back.

We use our muscles in such a way as to make the ground reaction forces push our right side forward and the left side backward. That means we want to create ground reaction forces corresponding to the red vectors in the picture.

If you don't know what ground reaction forces (GRFs) are, here is a quick tutorial. (I hope to have a better and more golf-specific tutorial in my biomechanics notes when they are complete.) And if you doubt the importance of ground reaction forces, check out this most instructive video; it shows very well what happens when you are missing exactly the GRFs we are talking about.

So what do we do in a golf swing to induce the GRFs in the previous picture?

Remember that a GRF is an equal and opposite reaction to the force your foot exerts on the ground. This picture shows red vectors that are equal and opposite to the GRFs in the previous picture. So the lower body has to move so the feet exert these "foot action forces". That implies a "scissoring" of the legs where:

The right foot kicks backwards, powered mostly by the trail gluteus maximus.
The left foot kicks forward, powered mostly by the lead quadriceps.

Those key muscles are shaded yellow in the picture. They are large, powerful muscles, with the ability to produce a forceful hip turn, leading to a powerful golf shot. In order to generate that power, the right glute and left quad must contract very forcefully in the downswing. Apparently I was doing it right, which turns out to be both good news and bad news. The bad part was that the powerful contraction tore a tendon connecting the right glute to my skeleton. Hence the need for physical therapy.

In what follows, I will skip the step of showing the foot action force and the muscle. I will assume you got the idea from this picture, so I will only show the ground reaction force, and discuss in words the muscles involved. You will have to remember that the muscles need to generate an equal and opposite force to the GRF.

Frontal forces

The GRF generated in the frontal plane during the downswing occurs in two phases:

The first half of the downswing, the force is mostly on the trail foot.
The last half of the downswing, the force is mostly on the lead foot.

If we were doing a full-scale detailed analysis, it would reflect that there is some action from each foot for the entire downswing. The net ground reaction force is exerted somewhere between the feet, closer to the trail foot early and to the lead foot later. We will treat them as separate, because (a) it is easier to understand that way, and (b) it turns out the frontal forces are not critical to our goal of a low-glute-action swing because they do not engage the trail gluteus maximus very strongly.

(The pictures for the frontal view of the normal swing are frame grabs from a YouTube video of Tiger Woods' swing.)

Any rotational acceleration is proportional to a torque exerted on whatever is rotating. The body will tend to rotate around its center of mass, or COM. (Engineers and older physicists will call it the Center of Gravity, or CG.) So to cause the body to rotate in the frontal plane, a torque has to be applied to the body in the frontal plane. That torque will be a moment of force around the COM, and that is what we will look for in all our frontal plane rotations.

In this picture, the red ground reaction force acts on a line that is forward of the COM. The yellow line is the distance from the COM to the force's line of action; that distance is the "moment arm". And the torque -- the moment of the force -- is the force times the moment arm. If you increase either the force itself or how much it tilts forward, you will increase the torque that drives the body rotation.

The force the body exerts on the ground is equal and opposite to the GRF in the picture. So it is a push by the trail foot downward and away from the target. That suggests that the principal muscles creating the foot action force are:

Any muscle that could lengthen the leg to push along the leg. The leg is already mostly extended; there isn't much trail knee flex at transition, so the quads are not in a position to do a lot. (It would be nice if they could, because the quads are big and powerful. They will do what work they can, but it is limited because of the limited angle needing to be straightened.) But the trail calf muscle (gastrocnemius) can be used to extend the foot itself, to get you "up on your trail toe", and that is where some of the push comes from.
Note that the force does not act directly along the trail leg. That suggests there is something moving the foot more outward, not just along the axis of the [fairly straight] leg. So we know the trail hip abductors are probably involved, rotating the whole leg in a direction away from the target.

In the latter part of the downswing, the trail leg is extended as much as it can. So it will not be generating large amounts of force against the ground. (In fact, even just the weight of the golfer will have been largely removed from the trail leg; if the swing is proper, the weight will almost be over the lead foot by this time.)

So any significant ground reaction force will be on the lead foot; the lead side (body and leg) will generate the foot's action force.

The lead quad is pressing the lead foot into the ground pretty forcefully at this point.
The lead side glute may be offering considerably help at this point. Earlier in the downswing, the glute was a lot less active; it had to let the quad's contraction push the lead hip backwards. But now it needs to stabilize the leg underneath the body, which calls for force from the glute.
You have seen the bigger hitters on TV actually jump the lead foot off the ground. This requires exerting a larger GRF, which is what provides rotational acceleration in the last 20-30% of the downswing. That would involve the lead side calf muscles. The jump has the added advantage of getting weight off the foot, allowing the body to rotate horizontally later and larger without a high torque injuring the lead leg.

The stack and tilt golf swing

Let us repeat what we just did, this time for the Stack and Tilt golf swing instead of the normal swing. We will look for the differences, particularly in the trail side gluteus maximus.

(The pictures of S&T forces are adapted from frames grabbed from a YouTube video of Nick Taylor giving instruction on Stack & Tilt.)

Horizontal forces

The image is taken at the same point as the earlier examples of the normal swing, the start of the downswing. But this time, the swing is S&T, which means Nick's weight is "stacked" over the lead (left) foot. Most of the vertical pressure he applies to the ground is through the lead foot; a lot less than half is in the trail foot.

That means his trail foot can't apply much kick-back force to the ground. Remember any horizontal force the golfer apples is a friction force. Friction requires a "normal" (that is, perpendicular) force, and the friction force itself can't exceed some percentage of that normal force. (I have a tutorial on friction force with more detail on this.) The S&T swing has a lot less weight on the trail foot, so it is very limited in how much frictional ground action force it can deliver. That means the trail side glute does not exert as much effort in a stack'n'tilt swing. The ground reaction forces in reaction to leg scissoring are still there, but much smaller than in the normal swing. It would be hard to get enough clubhead speed to play effectively with no scissoring GRF at all, but that force couple is not supplying nearly as much torque as in a conventional swing.

So where does the energy come from in S&T? As the picture shows, the hips are not getting much effort from the frictional ground action forces. So they have to be turned primarily by a frictional (horizontal) ground action torque exerted by the lead leg. The lead leg turns forcefully around its axis. With the majority of the weight being on that leg, there is a lot of normal force allowing plenty of torque to drive the swing.

Even so, it probably does not give as forceful a hip turn as the standard swing. With most of the body rotation being driven by lead foot ground reaction torque, we need to look at what muscles provide axial torque to the lead leg. That would be the internal hip rotator group of muscles, seven smaller muscles in the hip -- not a big, powerful muscle like the gluteus maximum. Moreover, none of these muscles has a lot of leverage in the horizontal plane, where we need the torque for rotation. Yes, there is still some measure of glute and quad action involved, but it is a lot less than what drives a normal golf swing. The combination of smaller, less-leveraged rotator muscles and much less glute and quad participation probably means a less powerful rotation.

Frontal forces

The frontal ground reaction forces for the S&T swing are similar to those for the normal golf swing, but generally smaller. That is because the hips start the downswing closer to the target, in a somewhat similar position to late downswing for the normal swing. So the trail leg is already a lot "longer" in S&T than at this point in the normal swing, and there is not much room to forcefully lengthen the leg (with the calf muscle) nor press the foot away from the target (with the hip abductors). Yes, there is some action of that sort, but considerably smaller than with the normal swing.

The late-downswing GRF is pretty simiilar to that of the normal golf swing, as are the muscle forces needed to induce the GRF. There really isn't much reason for them to be different. That phase has the weight forward in both swings, and of course the same general goals of the swing. So we could expect the lead quad to be the most important contributor, but also the lead side glute. And, if the golfer goes for extra power by jumping the lead heel or even the whole foot off the ground, the lead calf muscles could become involved as well. (Nick has only a bare minimum of "jump" in the video, so it isn't illustrated here.)

So there are a number of differences in muscle use between the normal golf swing and stack & tilt. The most significant for our purposes here (and perhaps the largest overall) is the trail glute's action being a lot less, with the horizontal rotation responsibilities transferred to the lead side internal hip rotators. That is promising for what we are looking for -- a swing that requires little exertion from the trail glutes.

My experience with Stack and Tilt

I decided to try S&T and see if it allowed me to play pain-free during my rehab period. The decision immediately raised three questions:

How much effort would it require to learn S&T? That is really an overhead for being able to play.
How effective is S&T as a golf swing? What do I give up -- or is it an improvement?
Does it allow pain-free golf while I rehab my right glute? This is the original question that started me on this line of thinking.

Let's look at these key issues.

Learning stack'n'tilt

This turned out to be remarkably easy. Bear in mind that I have been playing golf for decades, and have significantly changed my swing, either temporarily or permanently, at least four times. So learning a new swing is not a new activity to me.

Even allowing for that, I was surprised how easy it was. I found this Nick Taylor video that seemed to be a good introduction. The "ten words" concept promised that he would cover what the essentials of the S&T swing are. As far as I am concerned, he fulfilled that promise. (I have not read Bennett & Plummer's book, which is the defining document for S&T, so I don't know for sure. But what Taylor presents is easy to learn and does provide what I was looking for, a swing where the weight is forward throughout -- in a 12-minute video.)

Since I had some time before I had to go to the range and try it out, I also took a quick browse through an Eric Cogorno video on the subject. (I know Eric from some golf forums, and I used to play at the course where he teaches; I had a pretty good idea that I'd get some good, informal wisdom from him.) This video was not instruction, but a chatty session that put stack'n'tilt into perspective. Eric's point was that almost everything about the stack'n'tilt swing was something you need for a good golf swing anyway, except for the "weight forward" part. His message was, "Don't be scared of it. The vast majority of stack'n'tilt is made of good keys for any golf swing."

I went to the driving range to meet my practice buddy. I intended to hit nothing but stack'n'tilt swings, unless it started to hurt; I was not going to be dissuaded by the golf swing not working. It turned out to be a non-issue. It worked from the very first swing! I had no trouble at all learning it. I wasn't hitting it all that far, but almost all my strikes were solid, and with pretty good direction and trajectory. So I was willing to take it to the golf course and try it there. And it worked during a round of golf as well.

Over the past month, I have played mostly stack'n'tilt, with the occasional normal swing to check how I was healing. Here is how I rate each of the five two-word pairs that concisely define S&T:

Two words	It's just plain golf	I used it easily	Comments
WEIGHT FORWARD		✔	This is why I am trying S&T. Keeping the weight forward may take the traill glute out of the swing. This part was very easy to learn.
SHOULDER DOWN	✔		I had trouble with this. Lead shoulder down is a great way to think about the backswing. But I had trouble with the downswing. I have tried a right-side swing in the past -- spent half a year on it -- and found that a left-side pull worked better for me. The "right shoulder down" key encourages an active right arm; it simply did not work for me. I eventually settled for "left shoulder down; left shoulder forward" instead. Worked fine!
HANDS IN	✔	✔	I don't need to work on this; my swing plane already does it.
ARMS STRAIGHT	✔	✔	That has been one of my productive swing keys, so it fits right in.
HIPS TUCKED	✔		This has been one of my problems with a conventional swing anyway. Focusing on it for S&T definitely helps performance, but I do have to work at it. But no more so than I had to work on it with the normal swing.

The bottom line is that I have adopted (and adapted) stack and tilt with success and not much difficulty.

How does stack'n'tilt compare as a golf swing?

Here are the differences I notice when I use stack'n'tilt:

My ball striking is fine -- perhaps more solid and more reliable than it was with the normal swing.
I am losing distance, but not a lot. On average, I lose perhaps a half club to a club. This should not be surprising, because there are a few biomechanical changes that substitute a weaker ground reaction force than the normal golf swing. Sometimes, especially with middle irons, I lose even more carry distance on a shot that felt and looked solid; no idea why.

I have the impression that S&T is a "remedial" swing. It is a serviceable swing for golfers that can't master a proper weight shift. It should serve that purpose very well; I think I am more reliable than I was with the normal golf swing at "ball then turf" contact -- and I wasn't bad at that before. But that benefit comes with a cost -- distance.

Well, perhaps a more precise statement would be a cost of clubhead speed. We always tend to equate clubhead speed with distance, but that isn't precisely true. It is more accurate to equate ball speed with distance. The difference between the two assertions? Smash factor. If the rest of the swing assures better ball contact, then it might work out to be a wash -- and I think S&T will do that for many golfers. Still, it is a little disconcerting to hit what feels and looks like a good strike land in the front bunker. I am going to have to recalibrate my distances from "shading" perhaps half a club to at least a full club.

Does stack'n'tilt allow me to play golf during my rehab?

Yes and no.

It certainly does a good job of protecting the trail glute from strain, and that was the goal.
However, it can strain other muscles and joints more than the conventional swing.

It puts a lot more responsibility on the internal hip rotator muscles. They are smaller and less powerful than the gluteus maximus, and have correspondingly smaller support. Therefore we could expect that to be the next point of failure.
I have noticed increased strain on my lead knee and ankle. The effect is so slight I can't be certain it is real and due to stack'n'tilt. But I think it is real, and if so it is easily explained. The horizontal hip rotation is now being driven not by the trail glute, but by an axial torque in the lead leg. And that torque would need to be transmitted from the internal hip rotators to the ground via the knee and the ankle.
Side tilt is not something the spine does very well nor very easily. Rapid and forceful side tilt is an invitation to injury. In fact, side tilt to the right side at impact and early follow-through is probably the biggest cause of golf-induced back pain. Rob Neal has reminded me that S&T introduces a new side tilt -- left side tilt in the backswing. It isn't nearly as violent as the right side tilt near impact, but probably represents a danger to the back over enough time and repetition. (Note that the sides refer to a right-handed golfer; opposite side for left-handed.)

On the course, I find myself playing stack'n'tilt almost all the time. A few times a round, I'll tell myself, "Let's go for it," and execute a full-on weight-shift-driven swing. If I believe what my body tells me, I'm not completely healed yet. I don't have serious pain, but I do feel a warning twinge. Still, reverting back to S&T after a twinge allows me to play pain-free, even twinge-free golf for the rest of the round.

And that was the purpose, right?

A few caveats about this study

This is not a scientific study. It is a serious but low-budget amateur relating some anecdotal evidence. Worse yet, the person doing the study is also the subejct of the study -- that should warn you of built-in bias.

If this were a professional, scientific biomechanical study, there would have been:

Multiple subjects, divided into a test group and a control group.
A full-body inverse dynamics analysis of each swing for each subject, using a mathematical model of the human body.
A statistical analysis of the results, giving a better idea of how much load has been removed from the trail glute by changing the swing.

If this were a professional, scientific medical study, there would have been:

Multiple subjects, divided into a test group and a control group.
A way to measure the degree of healing of the torn glute.
A statistical analysis of the results, giving a better idea of whether changing the swing promotes better healing. It is entirely possible and even likely that it is just improving my mental health by allowing me to play golf while I recover. It is even possible that stack'n'tilt, minimal as the strain on the glute may be, retards the healing rather than promoting it.

Here's another caveat. I am rehabbing a damaged gluteus maximus, not a damaged spinal disk. It is unlikely that stack'n'tilt will provide the same relief for a disk problem. The cause of disk herniation and compression is a combination of:

The force of the golf club's release pulling the shoulders toward the clubhead via the arms.
Right side bent (for a right handed golfer).
Rapid rotation.

Biomechanics-PhD golf instructor Kiran Kanwar has discussed this at length; here's a current example of her exhortation. Her recommended solution is a swing she invented for the purpose, which she calls the "Minimalist Golf Swing". Its hallmark is a level shoulder swing, which eliminates side bend.

Note that the "second commandment" of stack and tilt is "shoulder down". That immediately says it is not a rehab enabler for a trail-side lower back problem, even though it can be one for a torn trail glute.

Acknowledgements

I'd like to thank Dr Robert Neal for his comments on my draft. The changes he suggested have been made, and the article is higher quality as a result. I also want to thank Peter Mannas, who caught an error and let me know so I could fix it before the article was publicly available for two days.

Last modified -- Oct 10, 2023