Does that mean if I am on a flat bench, lower a 100lb down, and press it up 1 foot, I am burning 0.0323832 (food) Calories? So would a 10 rep set is 0.323832 Calories? 10 sets or 100 reps would be 3.23832 Calories?
I am ignoring the energy used to lower the weight after each repetition and also ignoring the other positive effects of increased metabolism that burns calories during/after a workout.
I’m just trying to gauge what kind of base # of Calories certain exercises will burn vs others… i.e. squatting 200lbs & moving the weight 2ft per rep vs bench pressing 100lbs & moving the weight 1ft per rep.
I am going based on intuition, and checking that against your math. If I took an hour to work out, I could expect to burn 600 calories in an hour. My body would burn about 200 on it’s own anyway, and lifting the weights would add in another 400.
I would expect to crank out about 200 reps, not always 100 pound each, but if the exercise was a major body part, it might average out to 100 lbs. That’s about 2 cals per rep, but each rep has a whole series of events going on that add in fractions of calories they need to take place.
The actual lifting component might require just the calories you mention, but your heart rate increases, your lungs contract and expand more, and supporting muscles are burning calories, too. Just clenching your teeth burns more calories. Sitting up, laying down, etc.
There’s a difference between calories expended and calories of work performed, remember. The difference is efficiency.
You might calculate that the lifting you did required 10 calories of work. But your body probably expended considerably more (maybe 50 calories) to accomplish that, just through inefficiencies in the conversion process.
Think of it this way: if you had a gasoline engine turn a generator, which in turn powered an electrical motor, there is no way you would get as much power out of the motor as you were getting out of the gas engine in the first place, since there are losses every step of the way. Your body, being composed of many linked mechanisms (both mechanical and chemical) will have many losses as well.
Of course, if you are TRYING to burn calories, these inefficiencies are a good thing…TRM
Let me bend this question just a little. Let’s say I have a 20 pound dumb-bell and I merely hold it at arm’s length for a period of time. Now, for only the period of holding it still, since work is force times distance, in this case I am doing no work since the dumbell is not being moved any distance.
But my arm sure gets tired. What is going on? Am I burning any more calories other than by my normal at-rest metabolism?
This is sort of like Charles Atlas’ concept of ‘Dynamic Tension’.
What happens when muscle exerts force yet without movement?
Uncle Fred - that is exactly what I was talking about: the difference between “energy expended” and “work performed.” Both can be measured in calories (or joules or ergs or watts or anything else), but the amount consumed (input) can be much more than the amount achieved (output). And output/input = efficiency. In your example, work performed is zero, so efficiency is zero. Still good exercise, though.
But let me ask again - do we know for certain that my arm is burning any more calories than the normal at-rest metabolism would? Your response (thank you) implies it is without explicitly stating so, and that would certainly be my expectation - but do we have a for sure ‘yes’?
WAG: Wouldn’t the work in that system therefore be chemical work, and not mechanical/kinetic work? You aren’t moving the dumb-bell, and you might appear to be perfectly still when you hold it out in front of you, but your body will still be using up energy (working) to keep your balance, counteract that turning moment from the dumb-bell, hold your arm up (not a resting state position, so requires work), grip the dumb-bell (again, your hand’s resting state is open, not in a grip), etc. Your body does a lot of work, it’s just not on the macro scale.
Unless there has been some significant advance during the last couple years, calorie expenditure during intense weightlifting is very poorly understood, but probably very high. However, the calorie expenditure required to recover from an intense weightlifting session is very high.
IANA biologist, but I suspect that there would be chemical and biological ways to prove that you are burning calories with your arm holding a weight extended, such as glucose depletion or lactic acid build-up or whatever it is that they measure. Still, a physicist would say that you didn’t *perform *(achieve) any work.
Regarding Uncle Fred’s question… is there a unit in physics for [Force] * [Time]?
In his scenario it sounds like you need to exert a force equal to the torque generated by gravity and the lever created by your arm and the weight. Would some unit in physics for Force*Time be appropriate to try and convert to calories to answer his question?
Nope, no more than you can say that your car engine is doing no work because the wheels are spinning on rollers.
Your car engine is doing work and consuming energy even though the entire vehicle remains stationary because the pistons are still moving, and so are the drive train and the rollers. There is every bit as much movement occurring as if the vehicle were travelling forwards at 100mph. The only difference is that the movement is rotary or cyclical so there is no net change in position of the entire machine. But the total amount of movement in the system remains constant
Your muscles are comprised of many hundreds of thousands of tiny linear motors. To hold a weight stationary against gravity they have to zip back and forwards furiously, each one taking its share of the weight for a fraction of a second and then springing back to get another grip before taking up the load again. That’s where the movement is occurring. And the total amount of movement is the same as the amount of movement if the weight were actually being lifted. The only difference is that the movement is cyclical so the entire system remains stationary
It might help you to to think of these systems like a circle of people with a medicine ball. Each person throws the ball to the next person in the circle when they receive it. If we make the people play for an hour then stop the game when the person who started out with the ball has it, there has been no net movement in the system. The people, the ball, even individual limbs are all precisely where they were an hour ago. Nonethless a shed load of work has been done and the people feel it. But because the motion was rotary the movement was confined to *within *the system, and the system as a whole experiences no net movement.
Yes. The simplest way to test this is simply to measure the amount of CO2 you breathe out while holding the weight and compare it to the amount you breathe out while not holding it. Since CO2 is our exhaust gas from burning “calories” the increase demonstrates that there has been an increase in the burning rate.
A physicist would say that you did perform work, but that the motion was cyclical so no net movement of the system resulted. The individual components of the system moved many miles, they just happened to end up where they started from, but that doesn’t alter the amount of movement actually undertaken.
Running a dozen laps has much the same effect. You always end up where you started from, but you nonetheless moved during the interval and did work in the process.
Gravity is a constant force acting on all bodies within its field. The pull of gravity close to the earth’s surface, such as in a gym constructed on the surface, is 9.8 meters per second per second (9.8 m/s^2).
When holding a dumbbell at arm’s length with your arm horizontal relative to the ground, you are pulling against the force of gravity with a lever effect. Your shoulder is the primary focus, the length of the lever being the distance from your shoulder to the first set of knuckles on your hand as you hold the dumbbell.
Yes, you are doing work through a lever pulling against the force of gravity. When the resistance you are applying upwards to hold the dumbbell equals the force of gravity pulling the dumbbell down, the system is in equilibrium so there is no apparent motion. If either force is out of balance, apparent motion, either up or down, results.
It’s not force times distance from fulcrum; it’s force times distance moved. If you’re just holding your arm out still, then the distance moved is zero.
Right, and so there is no work done according from the standpoint of basic physics. That is, you didn’t do any more work than a weight rack holding the dumbbell.
However, you do expend energy to maintain that equilibrium. Some folks would say that therefore work is occurring at some scale. I got into one of these discussions in another thread. See post #24 by Blake in this thread. IANAP so you can reach your own conclusions about that position.