Shot Put Physics – Bench Press vs Clean and Jerk

shot-put-2

Check out this article on the physics of the shot put.  (The original paper can be found on the Arxiv, if you want to see the actual math – I promise it’s fun!)

For more than 30 years, sports scientists have puzzled over why the optimum angle of release for a shot put is not 45 degrees.

One of the stranger Olympic sports is the shot put, an event in which an athlete throws a grapefruit-sized sphere of metal as far as possible, using a strange throwing motion specified by the rules.

Now here’s a curious puzzle of biomechanics: at what angle should the shot be released to maximize the distance of throw?

I’ll just overlook the “one of the stranger Olympic sports” comment, for now. 

The Basic Physics

The article does bring up some interesting ideas that a shot putter (or “rock putter” for all you Highland lads and lassies out there) may want to pay attention to. 

The first is one everyone who engages in the sport already knows:  the height of the thrower matters.  I’m only 5’6’’ and am at a distinct disadvantage vs my lifter Chris who is over 6 feet.  If we each applied identical force, at an identical angle, his would go farther simply because it started higher.  (Think of the extreme case of a guy throwing from the ground or from the top of a 30 story building.)

shot-put

But, that isn’t all.  Additional arm length also matters.  There are likely a few reasons for this.  The first is simply that a longer arm increases the time the weight is under force before released.

The second reason is that the point at which you let go of the weight is the real height of release – not the shoulder.  If we have two people with identical shoulder heights, identical technique, and identical ability to put force on the implement, but with the first having an arm that is 2 inches longer; then the first person will be releasing the weight at a different height than the second.  The longer armed thrower will release just a touch higher – and therefore throw it farther.  All it takes is half an inch to win.

However, it turns out that the real height is determined by the angle of release and the velocity squared.  The velocity is basically the force you put onto it during your driving phase right before release.  That is, it’s all the work you did.  Since this parameter is squared, then you’re getting more “bang for your buck”. 

This is probably the reason the shot put technique has evolved the way it has over time – with shorter athletes preferring the spin technique which increases the time under tension, adds centrifugal force, and gives you a longer amount of time to accelerate.  They are compensating for a lack of release height by increasing velocity on the weight.

[By “shorter” athlete I mean under 6’ 5’’.  Seriously, these folks are monsters.]

The down side of increasing the force on the implement is that it tends to lower the angle of release. But, again, since you have velocity being squared, it’s a worthwhile trade off – especially if you don’t have the natural height.

Lack of Experience Showing

kara451bench_at_chest

Now … this is where things in the article get ugly, and silly. 

Finally, Lenz and Rappl say it has long been known that world records in bench-pressing are significantly higher than for the clean and jerk. This implies that athletes have greater power at their disposal when the angle of release is 0 degrees compared to other angles. This effect also means that a smaller angle of release could send the shot further.

The bold is mine.  That implication is false.  This isn’t to say that a lower angle of release doesn’t provide more power.  But, if true, their “implication” isn’t the reason.

It’s paragraphs like this that cause so many coaches and athletes to outright dismiss research and theory all together.  It shows an obvious lack of understanding of the very basics of shot put technique, bench technique, and what is happening in a clean and jerk.  And that is a shame, as there is a lot coaches and athletes can learn from well-designed research.  Practice and Science should be complementary.  Imagine if doctors just ignored science … it’d be the middle ages all over again (leeches!).

You DON’T drive with your arms and upper body in the shot put as your primary generator of force!  It’s a leg exercise.  Your upper body is in a purely supportive role.  Yes, upper body strength and power is very important, but not nearly as important as leg power.  Not even close.  

This is the reason throwers have long known that if you had to pick between only doing bench, or only doing clean and jerks, you’d pick the clean and jerks.  Why?  Because the bench is an upper body exercise while the clean and jerk is fundamentally a leg exercise that (just like the shot) uses the upper body only in a supportive role.  More over, like the shot, the clean and jerk is an explosive exercise that builds and develops power, where the bench is a slower pure strength move.  (Every coach knows the difference between strength and power.  Sports scientists should too.)

The reason bench press numbers are so far above that of clean and jerks isn’t because of the “angle”.  It’s because of bench shirts and a drastically lowered range of motion via arching. 

Those 1000 pound benches you see are ALL shirted. 

Raw (no shirt) bench presses are about 700 pounds.  Top clean and jerks are about 250 kilo’s or 550 pounds. 

But, again, the bench technique used in contests has a massive arch in it which dramatically reduces the range of motion.  How much?  Well, one of my own lifters holds world records in the bench press and has a range of motion in that exercise of less than 2 inches … yes, 2 inches! 

I’m not against that.  That’s the sport.  That’s the technique.  And that’s fine. 

But, let’s not pretend that the numbers seen in competitive bench presses are related – in any way – to the way one goes about throwing a shot. 

And by the way, by adding in an arch like that to the bench you decrease the angle to as far as –45 degrees from the shoulder (less than zero degrees)! Imagine throwing the shot with a negative angle! 

But, fundamentally, the technique of the two exercises with regard to angle is beside the point.  What is important is that benching is an upper body exercise – and shot put isn’t.

When you shot put, you are driving at maximum speed with your legs, ending in a full triple extension of the hips, knees, and ankles (especially for shot putters who use the “glide” style – see videos below).  Your upper body is held tight so that you don’t absorb any of the force generated by your legs and it is instead transferred into the weight, and your arm is used only at the last moment (just like a jerk) at the very top of the movement to give it a little extra push. 

Think of pushing a car.  You can’t possibly push-start a car by only pressing with your arms.  In fact, most people will keep their arms stationary and drive hard with their legs to get the car going.  Only once the car is up to speed do the arms start to move – giving that little extra “nudge”. 

The jerk is the same.  You drive with your legs like you would in a powerful vertical jump, and only at the top, when the arms are already 1/2 to 3/4 extended do you drive with the arms.

If the authors had ever done these three exercises – bench, shot put, and clean and jerk – they would never have said something so ridiculous.  And their article might get read by people who DO do these exercises.

They’re lucky I have a math degree and like research.  The truth is, the original paper is good, very interesting, and applicable.  But, by showing their glaring lack of real-world knowledge and experience they are turning off a large potential audience – the very people who would benefit most from the information.

Spinners

Take a look at this video of shot put “spinners” and tell me why the bench makes sooo much sense for them:

Gliders

And here are the “gliders”:

 

[Hat tip: Beth]

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