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Lifting Bro's Use Physics Too!



"Bruh do you even lift?", is now a common phrase often heard in our modern world. And while many people think lifting is just a bunch of knuckleheads throwing around weights, in reality it a strenuous exercise that demands perfect technique and lots of practice.

So I decided to look into the physics behind lifting to prove my point.

I started with benching one of the most well known exercise.

A basic workout for me would consist of a warm-up of 10 reps at 135 pounds, then 10 reps at 185, 8 reps at 185 and then 10 reps at 165.

If you look simply at the force required for each set you find some impressive results.

The force that would first have to be exerted just to lift the bar in the first set would be the weight in kg times the acceleration due to gravity.

Warm-up: 600.103 Newton's/rep

Set 1: 822.36308 Newton's/rep

Set 2: The same as set 2

Set 3: 733.45846 Newton's/rep

This is of course assuming that the lifter is using good form and therefor bring the bar down and up at a near constant velocity to get the most out the workout.

If we are to change our view though and instead look at energy involved in "repping" the weight we find some more interesting results.

You would find the energy required in each rep most easily by finding the change in potential energy of the bar as each rep is performed. Potential energy is found with the equation mgh, or mass times the acceleration due to gravity times the height of the bar. The mass of the bar is constant for each set and so is the acceleration due to gravity, so the change in potential energy would be those constants times the change in the y-plane. The change for me when my arms are extended to bench is around 20 inches, or .508 meters. The energy for each rep and then for each set are shown below.

Warm-up: 304.85 Joules/rep AND 3048.52 Joules total for this set

Set 1: 417.76 Joules/rep AND 4177.6 Joules total for the set

Set 2: 417.6 Joules/rep AND 3342.08 Joules total for the set

Set 3: 350.02 Joules/rep AND 3500.15 Joules total for the set

This comes to a whopping total of 14068.35 Joules expelled for the entire workout! This would be about enough energy to power a light bulb for around 2.3 minutes, which may seem not like a lot but compared to the little amount of effort people usually believe lifting takes it shows you a lot. Also to consider, this is only just one exercise of a workout that would surely include many more and obviously use more energy.

So don't look down at those lunkheads clunking around your local gym as you jog on the treadmill, because they're working hard just like you.

Picture from www.yiddishecup.com


Recommended Comments

Great post, I love it.  We actually did a crossfit workout last year where our score was determined by the total number of pounds lifted from the ground to over our head in a set time.  When we were done it was pretty cool to actually go calculate how many joules of work we did (was close to 50,000 joules per person).  It'd be cool to try to estimate how many joules of energy you used in an entire workout, then calculate your power output for the workout.  You could even find out how many slices of pizza that workout was equivalent too (never enough!)


And there's TONS of physics and technique in lifting.  My best clean and jerk is ~185 pounds, yet there's an athlete at our gym who is close to 50 pounds lighter than me whose C&J is 285. Strength is important, but it's also all about knowing how to move to maximize your strength!




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