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Calculating Power Exertion for Exercises

Calculating Power Exertion for Exercises

Q) Ray, can you calculate the amount of power it takes to perform the following exercises: squat, Deadlift, Push-Press and Biceps Barbell Curl?

A) I sure can.  Answering this question takes me back to my Physics 101 days.  To be able to perform the calculations of how much power each of these exercises takes, let me give you a Physics 101 refresher.

Physics 101: Power and Work

Power is defined as the work (W) done in a unit of time (t): P = W/t.

Work is defined as Force (F) x Distance (D): W = F x D

Therefore, Power can be defined as P = (F x D)/t

Distance (D) is the distance or displacement of the object being moved.  The greater the Force (F) and the greater the Distance (D) over which the force is being applied (the weight is moved), the more Work (W) is done.

Foot-Pound of force is the energy transferred on applying a force of 1 pound-force through a displacement of 1 foot. (For interests of calories burned, 1 ft lbs = .323832 calories)

Calculating Power Required Performing each Exercise

Where most people get confused doing these calculations is by making them too complicated by trying to figure out the force of gravity, the momentum it takes to start the weight in motion, the weight of the lifter, and other external factors.  For simplicity, these factors will not be taken into consideration.

To be able to calculate the Power for these exercises I will take the amount of weight for each exercise that I can do comfortably, in a controlled manner; and can perform 10-12 reps on my first set.  They are as follows:

  • Barbell Squat: F = 115 lbs.
  • Deadlift: F = 85 lbs.
  • Push-Press: F = 55 lbs.
  • Barbell Bicep Curl: F = 55 lbs.

(I’m an ultra trail runner not a power lifter, hence the weights are pretty low)

Next, to calculate power you need to measure the distance it takes to perform each of the above exercises.  For me, each of these exercises covers the distance of:

  • Barbell Squat: D = 15 inches  = 1.25 ft.
  • Deadlift: D = 22 inches = 1.83 ft.
  • Push-Press: D = 21 inches = 1.75 ft.
  • Barbell Bicep Curl: D = 36.5 inches  = 3.04 ft. (this is longer than the others because of the path of the arc)

Finally, to calculate power you need to calculate the time it takes to perform each of the above exercises.  For me, each of these exercises take:

  • Barbell Squat: t = 3.12 seconds
  • Deadlift: t = 2.34 seconds
  • Push-Press: t = 3.16 seconds
  • Barbell Bicep Curl: t = 3.84 seconds

Barbell Squat

Work = F x D = 115 lbs. x 1.25 ft = 143.75 ft lbs

Power = W/t = 143.75/3.12 seconds = 46.07 ft lbs/second

Deadlift

Work = F x D = 85 lbs x 1.83 ft = 155.55 ft lbs

Power = W/t = 155.55 ft lbs/2.34 seconds = 66.47 ft lbs/second

Push Press

Work = F x D = 55 lbs x 1.75 ft = 96.25 ft lbs

Power = W/t = 96.25 ft lbs/3.16 seconds = 30.46 ft lbs/second

Barbell Bicep Curl

Work = F x D = 55 lbs x 3.04 ft = 167.20 ft lbs

Power = W/t = 167.20 ft lbs/3.84 seconds = 43.54 ft lbs/second

Conclusion

Let’s see what happens when I leave the weights and the distances the same, but decrease the amount of time it takes to perform an exercise.  I will use the Barbell Bicep Curl as an example.  Let’s say that I can perform the exercise in 2.84 seconds instead of the 3.84 seconds that it actually takes me.  Here is the revised calculation:

Barbell Bicep Curl

Work = F x D = 55 lbs x 3.04 ft = 167.20 ft lbs

Power = W/t = 167.20 ft lbs/2.84 seconds = 58.87 ft lbs/second

As you can see the amount of Power that it takes to perform the exercise faster increased the by 15.33 ft lbs/second.  Therefore, the amount of power generated depends directly on the amount of time it takes to accomplish the work. the faster you do the work (lift the weight), the greater the amount of power. And inversely, the slower the work is done; the less the power.

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