A forum member posed the followi

A forum member posed the following question-: "Dr Mann, Have you ever listened to this podcast by Dr Sasho Mackenzie and do you have any opinions concerning his claims?

golfsciencelab.com/increased-clubhead-speed/

It seems he has found some correlation between ground force and clubhead speed. I don't think it proves increased ground force causes an increase in clubhead speed but that it is somehow connected (by something called 'Principal Component Analysis').

If I have interpreted this podcast correctly , he says that one should have 'as much ground force under lead leg as possible' at clubshaft vertical in the downswing. That even though the 'pull down' of the club is high at shaft vertical while ground force measurement should be low (ie. Newtons Third Law), one MUST endeavour to create 'as much ground force as possible' under the lead foot. This is to enable one to create momentum up and back to prevent the 'CF' forces of the clubhead pulling one off balance through impact."

I think that Sasho's reasoning is highly flawed.

First of all, you need to watch this other video where Sasho admits that this "idea" (that there is a strong correlation between an increased COP reading under the lead foot at P5 and clubhead speed) doesn't necessarily apply to reverse foot golfers.

Sasho argues that a golfer needs to significantly increase the COP measurement under the lead foot at P5 in order to maintain one's balance and avoid falling too much towards one's toes in the later downswing and through impact. Sasho also claims that this advice particularly applies if the golfer pushes more aggressively off the rear foot at the start of the downswing in such a manner that it may cause the COM to move too much from the heels towards the toes. That "opinionated claim" may apply to golfers who use a right hip spinning type of pelvic motion where they activate the right-sided gluteus maximus muscle that can not only cause right hip spinning, but can also cause early extension where the right buttocks leaves the tush line too soon between P4 and P5. Lexi Thompson is an example of a golfer who manifests that pelvic motion pattern and she even gets up onto her toes at impact, and I could readily imagine that she may need to brace herself by increasing the COP under her lead forefoot earlier (and possibly more forcefully) in the early downswing in order to maintain her balance in the later downswing and through impact. However, that pattern is not typical of all pro golfers.

Many pro golfers use the "pro golfers" pattern of pelvic motion between P4 and P5, where they activate their right-sided lateral pelvic rotator muscles while keeping their right-sided gluteus maximus muscle quiescent. That will cause their left buttocks to move back towards the tush line while they keep their right buttocks against the tush line and their COP measurement under the lead foot will be more towards the lead heel rather than the lead toes (as seen in Cordie's COP tracing). That type of pelvic motion pattern will not cause the golfer's COM to move towards the toes and the golfer should therefore not be predisposed to losing his balance - therefore there is no rational reason why the golfer would need to have his overall-COP reading move more quicker towards the lead foot between P4 and P5. In fact, in order to "stabilise" the right left/foot during the transition to the downswing (which is necessary for the contraction of the right-sided lateral pelvic rotator muscles to rotate the pelvis counterclockwise away from the "stabilised" right femur), the golfer needs to maintain sufficient weight-pressure under the right foot for slightly longer between P4 and P4.5. Jason Day manifests that pattern and his COP reading under his rear foot increases from 80% at P4 to 90% at P4.25 before it rapidly moves towards the lead foot. Sasho's other unscientific claim is the opinion that having the COP move towards the lead heel (rather the lead toes) is also associated with an out-to-in club head path and a predisposition to hit a fade. I think that Sasho's claim is totally unscientific and I think that it has zero merit. Whether the COP moves towards the lead foot's heel, rather than the lead foot's toes, is more reflective of the pelvic motion pattern used by the golfer, and not the pattern of upper torso motion, which is the major predictive factor that can predispose to an OTT move and an out-to-in clubhead path.

Finally, Sasho seems to imply that Bubba Watson has to really increase his COP reading by a greater amount under his lead foot because he moves his lead shoulder socket up-and-away through impact to a large extent. However, I suspect that Bubba Watson is a "reverse foot" golfer where the COP reading under the lead foot decreases between P5.5 and impact.

Sasho also claims that Rory McIlroy really ramps up his COP under his lead foot after P5.5 and that it helps him to rotate his pelvis even faster. That claim is not true!

Here are capture images of Rory McIlroy's downswing and one can see that his pelvis gets open by P6 (image3), but it doesn't rotate fast between P6 and impact and a 3-D stuidy has shown that the rotational speed of his pelvis is decreasing a lot during his later downswing, and that it actually reverses direction very soon after impact.

The following graph shows that Rory McIlroy's pelvis slows down in the later downswing even though he is a front-foot golfer where the COP under the lead foot increases dramatically in his later downswing.

Another comment - Sasho MacKenzie refers to swinging a sledgehammer downwards towards the ball and how a golfer must pre-react (react in advance) by increasing the COP under the lead foot to prevent a loss of balance due to the sledgehammer swinging downwards (parallel to the inclined plane). I think that's an irrational analogy because the sledgehammer is very heavy, while a golf club weighs so little that its downward momentum between P4 and P6 should not de-stabilise a skilled golfer and make him fall in the direction of his toes.

The forum member then asked-: "With regards the 'sledgehammer' comment above ,can we not also consider the weight of the arms being swung down as they weigh approx 8 lbs each?

On another issue ,I've been looking at this video of Justin Thomas COP trace. It looks like JT is a 'rear foot' golfer whose COP moves from the right to left foot almost instantaneously in the early downswing and then moves back to the right foot by impact."

My reply-: "I don't think that the downward movement of the arms creates a large "force" that will topple a golfer forward in the direction of the toes during the early downswing because they are still suspended from the shoulder sockets (which are not moving groundwards). There is also virtually no change in the body's COM motion in the early downswing.

Justin Thomas uses a right hip spinning pelvic motion and he only develops a lot of posterior pelvic tilt and extension in his later downswing.

Here are capture images of his downswing action.

Note how he thrusts his right pelvis forwards at the start of the downswing and that causes his right buttocks to immediately leave the tush line - image 2. I suspect that he is pushing actively off his right foot at the start of the downswing and that causes his right heel to immediately raise up as his right pelvis moves forwards and his right knee "kicks-in", and as he immediately transfers his COP rapidly to his lead foot so that he has most of his COP measurement under his lead foot by P5. I think that he is likely activating his right gluteus maximus muscle between P4 and P5, but it is not causing early extension because he is not "stabilising" his right femur in its P4 position (where it was relatively vertical) and he is actively increasing the degree of right hip joint flexion by activating his right iliopsoas muscle while simultaneously increasing his degree of right knee bend. I do not think that he uses his right-sided lateral pelvic rotator muscles at all during his early downswing.

Here are downswing capture images showing that he does not drop his head during his downswing.

Note how much higher his hip joints are at impact (image 3) compared to P5 (image 2) and note that his right hip joint is far less flexed - and I suspect that both gluteus maximus muscles are actively contracting. At impact, his spine is extended and he has posterior pelvic tilt, but he maintains the same degree of bent-over posture (which prevents his head from lifting) by acquiring a lot of right lateral bend and secondary axis tilt (which is best seen on face-on view images).

Because Justin Thomas thrusts his right pelvis towards the ball-target line so assertively in his early downswing, he needs to actively transfer his overall COP measurement (represented by that moving round ball object on his COP tracing) to his left forefoot by P5, and that helps him to brace his left side and that prevents him from losing his balance secondary to his right hip thrusting motion- as Sasho MacKenzie suggests is routinely necessary (but it is obviously not necessary in a golfers who use the "pro golfers" pattern of pelvic motion).

Also, note that Justin's COP measurement remains under his left forefoot in his later downswing and it never moves back to his left heel (as it would routinely happen in golfers who use the "pro golfers" pattern of pelvic rotary motion where the left buttocks moves back towards the tush line while the right buttocks remains on the tush line). Finally, note how Justin elevates his left heel through impact and how the "COP-ball" moves very rapidly to his right foot through impact. It is amazing that all his COP measurement is under his right foot soon after impact (making him a reverse foot golfer) - even though his right heel is still elevated off the ground. He must have very good biological balance control mechanisms in play to avoid losing his balance through impact - considering the rapid shifts in his COP measurements through impact.

Another forum member asked-: "Anatomical question for you first: Is it anatomically easier (or more efficient) to accelerate the torso and have it acquire the greatest rotational speed when the left knee is bent and and then straightens shortly after the torso begins to accelerate? Hips can be included with torso since they should rotate for the torso to acquire the greatest rotational velocity.

I ask because my thought is that, if the answer to my question is yes, then the degree of GRF under the left foot is the result of a technique to best acquire rotational velocity of the torso and, likely, the greater the rotational velocity, the faster the left knee would straighten."

My reply-:

I believe that one first needs to separate pelvic from upper torso rotation, and the question then becomes what is the fastest way to rotate the pelvis during the downswing. I answer that question by dividing the pelvic rotary motion into two phases - the hip squaring phase (roughly between P4 and P5) is phase 1 and the open phase (roughly between P5 and impact) is phase 2. If a golfer rotates his pelvis 50 degrees clockwise during the backswing and gets to impact with his pelvis 50 degrees open, then he has 100 degrees of pelvic rotation happening during his downswing action (roughly divided equally between the two phases). To rotate the pelvis optimally fast between P4 and P5 (phase 1), I think that it is advantageous to use the right sided lateral pelvic rotator muscles to rotate the pelvis counterclockwise away from a "stabilised" right leg + use horizontal GRM's produced under the left forefoot as the golfer pushes away from his toes (away from the ball-target line). To efficiently push off the left forefoot in a direction away from the ball-target line, the left forefoot must be weight-pressure loaded, but it does not mean that the left forefoot has to be maximally weight-pressure loaded during phase 1. During phase 1 (which ends with the golfer in a "Sam Snead sit-down" posture), the left knee is still bent and not straightening. Left knee straightening often happens in phase 2 when the golfer contracts his left quadriceps muscles to straighten his left knee and contracts his left gluteus maximus muscle to extend his left hip joint and simultaneously pulls his left hip joint counterclockwise so that the left buttocks rotates counterclockwise away from the target. During the early part of phase 2, the vertical GRF will likely be high under the left foot and it then decreases during any "jumping-up" motion happening later during phase 2. I know of no correlation between the timing/speed of left knee straightening and the speed of pelvic rotation during phase 2. Some pro golfers (like Tiger Woods) have a lot of left leg straightening happening between P5 and impact, while others (eg. 2015 long-drive champion Tim Burke) retain a lot of knee flex into impact and yet still have a good pelvic rotation during phase 2.

Capture images of Tin Burke's downswing action.