Running improves
My lunchtime run was quite a bit quicker today so perhaps my fitness is edging it's way back - though the big belly is still evident.
My times for the 3.53 mile route (middle mile is muddy) over the last week have been:
18 Jan 33:01 Pace 9.22/mile (8:59; 10:10; 9:12) 470 calories
20 Jan 31:10 Pace 8.56/mile (9:01; 9:53; 8:09) 485 calories
23 Jan 29:46 Pace 8.30/mile (8:28; 9:08; 8:06) 495 calories
So, it seems like a good improvement but the middle mile is a bit of a wildcard because the weather dictates the condition of the snow/mud.
Can anyone explain why moving the same mass the same distance, albeit at different speeds, uses more energy? I assume it is more to do with chemistry than physics!
posted by litsl @ 3:58 am
4 Comments:
Hi Carl,
Re question "Can anyone explain why moving the same mass the same distance, albeit at different speeds, uses more energy?"
Not sure if you really wanted an answer but as I've got exams on Sunday and it won't do me any harm to do a bit of physiology revision, here goes: (it's a wee bit more complicated that this but in a nutshell...)
The human body is made up of trillions of cells; all cells in the body need energy to perform their functions and to reproduce.
However, cells can't use food in the format that we feed the body, i.e. bread, fruit, meat etc, so the body has lots of techniques e.g. saliva and stomach acid to break down the food into it's component parts: sugars, proteins and fats.
Within the every cell in the body* there are tiny manufacturing sites called mitochrondria that then break down these component nutrient parts even further so that it can be converted to ATP (Adenosine Triphosphate), which is effectively a 'battery' that stores the nutrients we eaten in a chemical form, ready to be used as energy.
ATP is the energy source that muscles need in order to contract. Muscles need to contract faster in order to increase speed. This means the muscles need more energy (ATP) than if they were moving at slower speeds, so the body releases more ATP to allow this to happen, i.e. uses more energy from the battery.
Eventually, once the battery is dying or dead, it needs to be recharged in order for more ATP to be available for release, therefore the body needs more nutrients (food) to breakdown to their component parts in order for the mitochondria to convert this to ATP, hence the increase in nutrient intake, i.e. calories.
*except red blood cells
Hope that makes sense...
Cheers,
Alex
PS. Had a horrible moment the other day - I'm sure I forgot to thank you for my christmas pressie!!!!! I'm mortified. Thanks very much - can't wait to use them and appreciate how much lighter my back pack will now be :-) Great gift!
Hi Alex
Nice to hear from you. Thanks for the biology explanation of turning food into energy, I struggle with understanding all that. However, I still dont get it. In physics, if you move a mass of 190lbs a given distance, 3.5 miles, you will need a certain amount of energy to do that - for arguments sake let's say 500 calories.
Speed is not a factor in the equation. If the mass moves at 1 mile/hour or at 10 miles/hour the same energy is used.
I think the difference in calories is perhaps from biomechanical efficiency. So, the way that lightbulbs that get hot are said to be very inefficient at producing light because wasted energy turns into heat. I think it is similar with running as opposed to walking. Walking is perhaps more efficient than running and so burns less calories. Not completely sure though.
Glad you liked the christmas present. I have another one for you and Doug on the way (I forgot I'd already got you one, perhaps I should save it for next year!).
Cheers
Carl
Hm. I struggle with the physics part so between us, oh dear! But, using your example, I don’t get that either:
Let’s say that the mass that you referred to was a car. It does take more energy to move it faster doesn’t it? That’s why the same car, with the same driver and the same contents, burns more fuel at 90mph than it does at 50mph.
Re my explanation on muscles, following on from the above, try this:
Muscles have to contract in order for them to move. To contract, they require energy. If you are running at 5mph, your muscles would need to contract (i.e. perform the running action cycle: legs up and forward, arms pumping etc) 50 times per minute. If you wanted to run at 6mph, your muscles would need to contract more times per minute, say, 60, in order to increase and maintain speed.
Muscles are made up of thousands of cells, every one of them requiring a release of ATP in order to work. If there are 1000 muscle cells in a particular muscle, that muscle would then need 1000 releases of ATP in order to contract once. If that muscle needs to contract 50 times per minute to run at 5mph, the muscle would need 50,000 releases of ATP to do so; to then run at 6mph (60 contractions per minute), that same muscle would need 60,000 (1000 x 60) releases of ATP, i.e., more ATP = more energy used.
Does that make any more sense?
Oh, and if you can’t remember that you’re already bought presents before you got here, I don’t hold out much hope for you remembering that you bought a second lot by next Christmas ;-)
Alex
Hi Alex
I think with a car the other factors at play become significant. Driving at 90mph involves significantly more wind resistance than driving at 50mph which accounts for quite some of that lack of efficiency. At walking/running speeds I would expect wind resistance to be less of a factor, though it is clearly some kind of factor.
I don't really get the muscle contraction argument because although they do contract more in a minute at 6mph, you get more distance as a result. So you get more distance for the energy put in.
All pretty complicated. I guess there are lots of factors at work here from the efficiency of muscles to wind resistance and combined, they perhaps explain those differences.
Cheers for now.
Carl
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