How many calories are burned doing a bench press?

Answer 1

energy = force * distance, so

energy = mass * acceleration due to gravity * distance.

Say you press 100kg through 0.5m for 10 reps (near the surface of the Earth):

energy =100kg * 10ms^2 *0.5m *10 reps.
=5000 Joules

5000 Joules converts to 1.195 dietary calories. This is the minimum amount of energy required to lift 100kg through 0.5m 10 times. But human muscles are only about 25% efficient, so multiply this by 4. Furthermore pushing weight at 80% of your max uses 12 times more energy than 20% of your max, i.e. your body is only a third as efficient when it is being strained, due to greater demands on your cardiovascular system and more secondary muscles coming into play.

So it is fair to multiply the 1.195kcal by 12 to give about 14 as the number of kcal used during the actual set. Following the set you will have increased respiration and circulatory flow for a while, which uses further energy on top of this.

This is a sound way of solving a question like this.

However, I would be interested in solving the question a different way (and this might make a good high school project).

The calculation above takes

mass * acceleration * distance * reps * best muscular efficiency* 80% efficiency

So 100kg * 10ms^2 *0.5m *10 reps * 4 * 12. What if the muscular effiency is 30%, What if 80% effort results in 14 times more effort, not 12? Big differences result.

So how to test this.

Wear a heart rate monitor for 10 minutes to get a base line heart beat. Then do the set. Record the increase in heartbeat for the next 10 minutes (if the heart beat is not down to resting, use a long enough time frame that it does. Caluclate the energy used by the resting heart, and by the bench pressing heart. Various formulas are available on the internet.

Here is one that seems to be on a number of web sites.

Using VO2max
Men: C/min = (-59.3954 + (-36.3781 + 0.271 x age + 0.394 x weight + 0.404 x VO2max + 0.634 x HR))/4.184
Women: C/min = (-59.3954 + (0.274 x age + 0.103 x weight + 0.380 x VO2max + 0.450 x HR)) / 4.184

Without VO2max
Men: C/min = (-55.0969 + 0.6309 x HR + 0.1988 x weight + 0.2017 x age) / 4.184
Women: C/min = (-20.4022 + 0.4472 x HR - 0.1263 x weight + 0.074 x age) / 4.184
weight is in kg

Answer 2

The answer is surprisingly low. Pullups are difficult because they're engaging relatively small muscles, but in terms of energy expended, it's roughly equivalent to walking up a single stair.

The first part of the calculation is based purely on physics. The amount of work done (or energy added to the system) during a pull up is the product of 3 factors:

1) Your weight in kg: I'm 70kg

2) Gravity, which you have to overcome: 9.81 meters per second squared

3) The distance you travel: Let's say 0.4m

That gives us 275 Joules. We'll convert to calories in a bit.

Your muscles, though, are not very efficient at moving your mass around. (Not all your muscle work moves your body perfectly, some heat is generated converting food to mechanical energy, which is why you get hot exercising.) Wikipedia says muscles are 18%-26% efficient. Let's use 22%.

With 22% efficiency, that 275 Joules becomes 275J/22% = 1,250J. Unfortunately, you need 4200J to make 1 food calorie... So that means doing a pull up has only burned 0.3 food calories!

There's some simplification and you need to tailor the inputs to your own body, but you're not going to get thin doing pull ups alone. If you want to lose weight, diet is a much more important component than exercise, especially anaerobic exercises like pullups.