Question

PLEASE HELP ME ! a 77 kg male looking to burn 120 calories for 30 minutes of swimming should choose the fast crawl stroke. t or f?

Answer 1

false all most 100 calories in 10 min
http://www.dailymail.co.uk/health/article-132028/Swim-away-calories.html

Answer 2

That seems low. I think a strong crawl burns closer to 400-500 calories per hour.

Answer 3

Remember a metabolic calorie is 1000 physical calories. So 500 cal. = 2,093,500 joules. If this is used over one hours that is equivalent to about 0.78 HP! A normal human over a sustained period can generate about 0.1 HP.

Using 500 cal per hour is like pressing 10 Kg 35,604 times in an hours or ~ 10 times a second.!!!

Most people would be lucky to use 70 calories in an hour. A good athlete might do 100-120 cal/hr.

Answer 4

I don't think that's right @gleem. Go here:

http://www.mayoclinic.com/health/exercise/SM00109

The Mayo Clinic doesn't seem super likely to make a mistake like this, and all the activities they list burn more than 200 kcal/hr for a 73 kg person. Even walking at 2 mph is 204 kcal/hr, they say. 200 kcal/hr = 200 watts, maybe about twice basal metabolism, and that doesn't seem hard for the human body to achieve. FWIW, they list lap swimming at about 400 kcal/hr for a 73 kg person. They claim a 73 kg person running for an hour at 7:30 per mile -- which almost any reasonably fit man can do -- would burn 860 kcal.

It's true to burn the same amount of calories per hour lifting weights is impossible, which is why you do aerobic exercise if you just want to burn a lot of calories fast, but this is because you're using the relatively small muscles in your arms instead of the big ones in your back and legs.

If I do a leg press, for example, I can easily press 280 kg. Let's say it's up and down 50 cm. That means each press is 2.7 kJ. I can do 10 of these in about 20 seconds, which translates to nearly 1400 watts, or 1200 kcal/h. Of course, I can't keep that up for an hour, but you get the general idea: if I use the big muscles, I don't see a really big problem generating power levels at 200-500 watts for an hour, and I'm sure someone like Lance Armstrong could do a lot better.

Answer 5

Oh drat, I forgot I meant lb instead of kg for a leg press. Bah. I'm sure there are people who *can* press 280 kg, but I'm not one of them. I meant 120 kg. So that means 1.2 kJ per press, and the power generated during the set is 590 W.

Answer 6

OK, your right it seemed a little? low. I know that the human body is not 100% efficient and that was not taken into account. Energy is conserved and is dissipated mostly through respiration and perspiration. If Mayo Clinic is correct then the body is only about 30 % efficient like a gasoline engine. Also the energy use they quote probably includes the basal metabolism of 50cal /hr. So out of every 100 cal they "burn" above that for basal metabolism they generate about 25 calories-100000 joules of actual work at a rate of 30 watts. equivalent to pressing about 5.5 Kg 50 cm per sec. for 1 hour (3600) reps.

I don't think the muscle group used has too much to do with the amount of energy used. It is a known fact that heavy weight lifting burns calories at a faster rate than aerobic exercise. Also the increased muscle mass has a higher metabolic rate which aids weight loss.

Answer 7

You've forgotten that bigger muscles are, well, bigger. You can always burn more energy faster using bigger muscles, just like you can burn gas faster in a 40 ton semi with a big diesel than in a gas-sipping Prius, even if you floor the latter. However much you can burn lifting weights with your arms, you can always burn more faster using large muscles groups with equal intensity. Consider what Usain Bolt burns in blowing down a 100m track in less than 9s. He sustains an acceleration of 0.5g in the first 20m, for axample -- a power output just in horizontal acceleration of 3.5 kilowatts, if I've done the math right.

Answer 8

Your right a bigger muscle does burns energy faster. I was intimating that for a given amount of work I expect the same amount of energy will be consumed whether you used your legs or arms. Also I did not mean that a human could not generate a lot of power. Just that the power generated was limited to a short time interval.

For Usain Bolt the 3.5 Kw was generated over 9 sec. so the energy used to do this work was about .009 Kw-hrs.~8 cal accounting for efficiency maybe 30 cal. To use 500 cal per hour he would have to repeat his performance more the 16 times in one hour. IMMIC

This showes that the power time interval product varies considerably with the time in which the work is performed.

This was an interesting discussion Thanks