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Body's efficiency

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 Robert Durran 03 Jul 2020

If I assume my body is a perfectly efficient machine for converting food into gravitational potential energy, it would be burning about 1000kJ when I walk up a 1000m hill. But how much energy am I actually likely to be burning?

I'm genuinely wondering, because, having for the first time in my life visibly put on weight during lockdown (I'm not too bothered since I've only been fingerboarding), now that we're allowed out I'd quite like to stop being a fat bastard.

Post edited at 14:03
 petemeads 03 Jul 2020
In reply to Robert Durran:

I think the efficiency figure food>output is about 23%, I tend to convert kJ to KCal and call this about right.

OP Robert Durran 03 Jul 2020
In reply to petemeads:

> I think the efficiency figure food>output is about 23%, I tend to convert kJ to KCal and call this about right.

Thanks. So would that roughly mean I could eat about 4000kJ and not get fatter as long as I walk 1000m uphill afterwards?

In reply to Robert Durran:

Probably not much help, but when I munro bagged, I had worked out a rule of thumb for myself: generally walking more or less according to Naithsmith's rule, I reckoned I used to average 300 - 350 kcals/hr walking in the day for both the ups and downs of the route, and specifically with 500 kcal/hr on any steep uphill sections.

 petemeads 03 Jul 2020
In reply to Robert Durran:

As long as coming back down does not have a storage component...

 petemeads 03 Jul 2020
In reply to Climbing Pieman:

Interesting. I have been looking at some of my Garmin estimates, having updated to a Fenix 6 with their latest algorithms based on heartrate variability. My son and I walked/jogged the Edale skyline a couple of weeks ago, faster than Naismith at 4mph, with 1,200m of ascent and 33km in 5 hours moving time. The Calorie estimate was 2,330. The initial ascent of Lose Hill was 2km, 290 metres gain and 230 Calories, taking 25 minutes, so not that far from your 'steep' estimate. Total mass about 65kg.

OP Robert Durran 03 Jul 2020
In reply to petemeads:

So presumably your Garmin  thingy has a built in formula for calculating energy expenditure in terms of speed, time and height gain - I suppose that is what I am interested in!

In reply to Robert Durran:

The Apple Watch will give you that too. And I’m sure other similar devices will do too. Apple will also give you a climbing option too on the workout icon so you can get the calorie burn from that too.

Good luck - stay slim !

OP Robert Durran 04 Jul 2020
In reply to I like climbing:

> The Apple Watch will give you that too. And I’m sure other similar devices will do too. Apple will also give you a climbing option too on the workout icon so you can get the calorie burn from that too.

I am extremely gadget-averse, so have no wish to buy one of those things - would be quite happy with a formula and my trusty pencil and paper

In reply to Robert Durran:

Understood

 girlymonkey 04 Jul 2020
In reply to Robert Durran:

I don't think there is a simple equation as our bodies are all different efficiencies! For starters, the size of your body makes a difference. It takes more calories to move a bigger body than a smaller one. Then fitness comes into it, age and I'm sure a raft of other individual factors.

The Garmin type watches give estimates based on your height, weight, age and heart rate, and I think they are a reasonable guess. I don't know how far off they actually are.

I guess if you don't want to use gadgets for it, you just play with different foods on different days and see what your body does with them!

 DancingOnRock 04 Jul 2020
In reply to Robert Durran:

My formaula for running is 

mass (Kg) x distance (Km) x 1.1 = Calories. 

It’s not potential energy, it’s work done. Lifting up 1m shouldn’t really be much different to pushing along 1m. You’re not storing the energy, you’re using it to overcome a resistance to movement.

Apologies for the non SI units. 

1
 petemeads 04 Jul 2020
In reply to Robert Durran:

I don't think the newer Garmin devices calculate energy expenditure from speed/distance/height gain at all. For example, I did a very hard treadmill session walking as fast as possible (4.8kph) up the steepest incline (15%) with 10kg on my back - 59 minutes gave 622 Calories for a 720 metre height gain. Of course I had not gone anywhere, distance was based on a footpod measuring paces. Heartrate averaged 140 and peaked at 155, I think this was the source of the Calorie estimate.

 Ean T 04 Jul 2020
In reply to Robert Durran:

> I am extremely gadget-averse, so have no wish to buy one of those things - would be quite happy with a formula and my trusty pencil and paper

Did you hear about the constipated mathematician? Had to work it out with a pencil.

OP Robert Durran 04 Jul 2020
In reply to DancingOnRock:

> My formaula for running is 

> mass (Kg) x distance (Km) x 1.1 = Calories. 

> It’s not potential energy, it’s work done. Lifting up 1m shouldn’t really be much different to pushing along 1m. You’re not storing the energy, you’re using it to overcome a resistance to movement.

Sorry, but I refuse to believe that running up a steep hill for a mile dies not burn more energy than running a mile on the flat! Gravity IS resistance to movement.

I'd also have thought that running a mile fast burns more energy than walking a mile.

OP Robert Durran 04 Jul 2020
In reply to petemeads:

You have gone somewhere relative to the treadmill!

I can believe that heart rate could be used; after all it is pumping the blood which carries the oxygen to the muscles which convert food energy into movement.

OP Robert Durran 04 Jul 2020
In reply to girlymonkey:

> I don't think there is a simple equation as our bodies are all different efficiencies! For starters, the size of your body makes a difference. It takes more calories to move a bigger body than a smaller one. Then fitness comes into it, age and I'm sure a raft of other individual factors.

I wonder how much fitness does come into it, rather than just allowing me to go faster. I suppose it might make me more efficient.

> The Garmin type watches give estimates based on your height, weight, age and heart rate, and I think they are a reasonable guess. I don't know how far off they actually are.

Well it would be interesting to know the theory or empirical method behind their algorithm!

 mrphilipoldham 04 Jul 2020
In reply to Robert Durran:

I think he’s mentioned this formula before, and when I cross referenced some of my Strava recorded runs it checked out, leaving me with roughly 1 calorie for every 10ft of height gained to add to the ‘flat’ distance total.

 girlymonkey 04 Jul 2020
In reply to Robert Durran:

> I wonder how much fitness does come into it, rather than just allowing me to go faster. I suppose it might make me more efficient.

The fitter you are, the lower your heart rate will be for a given speed/ distance. So presumably you will have to keep going further or faster over time to keep burning as many calories.

 DancingOnRock 04 Jul 2020
In reply to Robert Durran:

You’d be wrong. You’re missing out efficiency and power. If you run you’re slightly less efficient but you go quicker. So you do use slightly more energy (not a lot, there’s more used in the up and down movement) but you use it in a shorter time. 
 

So your power output is a lot higher. you do the same amount of work. 
 

Also if you walk and take longer, your basic metabolic rate (about 100cals an hour) starts to influence things. A 6 mile walk would take 2 hours - 200 cals. A 6 mile run might take 40mins 60cals. 
 

We aren’t machines. 

1
OP Robert Durran 04 Jul 2020

> Also if you walk and take longer, your basic metabolic rate (about 100cals an hour) starts to influence things. A 6 mile walk would take 2 hours - 200 cals. A 6 mile run might take 40mins 60cals. 

So why am I a lot more knackered after running rather than walking the same route?

Is it just that I am also recovering while walking?

> We aren’t machines. 

Really?

Post edited at 09:37
 DancingOnRock 04 Jul 2020
In reply to girlymonkey:

Yes. But it’s mainly weight and distance for the average person. 

If you’re an elite athlete you have efficiencies in the way you move and the rate you can get oxygen out of the air you breathe. Which just means you can go faster. They burn the same number of calories running a marathon in 2 hours as the rest of us do in 4 or 5 (assuming we weigh the same) 

OP Robert Durran 04 Jul 2020
In reply to DancingOnRock:

> Yes. But it’s mainly weight and distance for the average person. 

And height gain!

 DancingOnRock 04 Jul 2020
In reply to Robert Durran:

Rate of work. It’s harder to convert the energy that quickly. It’s not fuel, it’s all the other damage you do to your system that makes you knackered. You’re also using a different fuel source. When you run the energy is coming from your muscles and liver, very quickly. When you walk it’s from your fat. At the end of the run all the energy has been removed from your muscles.  
 

We are not machines. 
 

Or if you were going to model the human as a machine, it wouldn’t have one fuel tank. It would have several. 

OP Robert Durran 04 Jul 2020
In reply to mrphilipoldham:

> I think he’s mentioned this formula before, and when I cross referenced some of my Strava recorded runs it checked out, leaving me with roughly 1 calorie for every 10ft of height gained to add to the ‘flat’ distance total.

That would sound reasonable, putting in some numbers.

 DancingOnRock 04 Jul 2020
In reply to Robert Durran:

1 cal per 10ft isn’t particularly significant though. A 3000ft climb would be about 300 calories. So it would depend I guess on how steep the climb was but over a day you’d have to do a lot of climbing to affect your overall expenditure. 

OP Robert Durran 04 Jul 2020
In reply to DancingOnRock:

> Rate of work. It’s harder to convert the energy that quickly. It’s not fuel, it’s all the other damage you do to your system that makes you knackered. You’re also using a different fuel source. When you run the energy is coming from your muscles and liver, very quickly. When you walk it’s from your fat. At the end of the run all the energy has been removed from your muscles.  

Fair enough. I think that's what I roughly meant by recovery. Running leaves deficits which need repaying?

Anyway, as far as losing weight is concerned, are we saying that walking and running the same route will be equally effective?

 girlymonkey 04 Jul 2020
In reply to Robert Durran:

youtube.com/watch?v=vuIlsN32WaE&

A video about the mathematics of where fat goes and how we lose weight. (Basically, you need to breathe more)

 Jamie Wakeham 04 Jul 2020
In reply to Robert Durran:

I always taught that the human body was comparable to a typical petrol car, in the region of 20-30% efficient.

When you're walking or running, you're transferring energy via three major mechanisms: the fairly steady background tasks of keeping yourself alive (which turns out to be in the region of 100W), doing work against air resistance, and gaining GPE.

Walking on the flat is primarily a case of transferring chemical energy to GPE, because your CoM bobs up and down with each step.  Air resistance is fairly negligible at these speeds.  The 'flatter' your gait, the more efficient you'll be - watch marathon runners.

If you walked a route and then ran it, you'd transfer more energy when running - both because the height gain made on each step goes up a bit, and also because air resistance becomes more significant.  It scales with a factor that's greater than v but less than v^2.  Drag is complicated when you aren't a ball-bearing falling in thick oil.  

Going uphill obviously adds an extra store of GPE, so you'll work harder.  But it's not as much as you would calculate by simply adding GPE=mgh to the energy burned by walking, because the bobbing up and down of your CoM as you walk is in the same direction as the gain of height from the slope, if that makes sense - some of the height gain of the hill is taken up by your 'natural' height gain as you walk.

 Dr.S at work 04 Jul 2020
In reply to girlymonkey:

Heart rate is only one of the things that affects Cardiac output - Stroke Volume is the other (how much your heart pumps out per beat).

Athletes tend to develop bigger hearts, so they can for a given HR kick out more blood (SV increases) but that still requires more energy. 

 nufkin 04 Jul 2020
In reply to Robert Durran:

>  as far as losing weight is concerned, are we saying that walking and running the same route will be equally effective?

More or less - though I might argue that as running means the route is over more quickly it - counterproductively - leaves more time for filling up with biscuits

OP Robert Durran 04 Jul 2020
In reply to DancingOnRock:

> 1 cal per 10ft isn’t particularly significant though. A 3000ft climb would be about 300 calories. So it would depend I guess on how steep the climb was but over a day you’d have to do a lot of climbing to affect your overall expenditure. 

I have standard local walk/run which is about 12km and 3000ft, so about 1500 cal of which 300 would be for the ascent. Seems a bit low to me, though still significant. If I ignore the "effortless" downhill half (which is a fairly small proportion of the time), it is relatively significant though. 

It might be worth working out how to maximise energy used in a given time slot - short and hilly, or longer and flat. For an hour's walk, Naismith would give 5km or about 500 cal, versus 2000 ft or 200 cal, which would suggest always best going for distance. This would certainly go against my intuition though - three hours on the flat feels easier to me than on the hills!

OP Robert Durran 04 Jul 2020
In reply to Jamie Wakeham:

> Going uphill obviously adds an extra store of GPE, so you'll work harder.  But it's not as much as you would calculate by simply adding GPE=mgh to the energy burned by walking, because the bobbing up and down of your CoM as you walk is in the same direction as the gain of height from the slope, if that makes sense - some of the height gain of the hill is taken up by your 'natural' height gain as you walk.

Though, the "bobbing" will be almost entirely in my legs whereas going uphill I am lifting my whole body's mass.

 DancingOnRock 04 Jul 2020
In reply to Robert Durran:

It greatly depends. Losing weight is a case of making sure your glycogen stores are kept relatively empty all the time so that when you’re resting you are converting fat to glycogen to top up your stores. 
 

Otherwise when you eat, all the energy you get from food gets converted straight to fat. 
 

So hard exercise will burn some fat, but mostly use glycogen while you’re exercising. Then over the next 24 hours you’ll convert fat to glycogen to top up the stores. 

Easy exercise will deplete your glycogen stores but mainly you’ll be directly using fat.

So huge long walks or lots of short walks, or basically not sitting around, would always be better than smashing yourself out and then sitting around all day.

Ultimately, the best way to lose weight is eat less and move more. Lots of people try the eat less  and lots of people try the move more. But one is useless without the other, you either eat more to compensate for the extra work, or you move less because you don’t have the energy.

The best exercise is one you enjoy, one you will stick with and fits in with your lifestyle.

So basically, don’t rush home after your run and eat the contents of the fridge. Reduce portions but maintain enough food to fuel your exercise.  

Post edited at 10:38
OP Robert Durran 04 Jul 2020
In reply to nufkin:

> More or less - though I might argue that as running means the route is over more quickly it - counterproductively - leaves more time for filling up with biscuits

Also, running certainly feels more deserving of biscuits...... and pasta, and wine.......

 DancingOnRock 04 Jul 2020
In reply to Robert Durran:

You’re bobbing up on the flat and uphill, just the bobbing down bit on the flat doesn’t use any energy and all the bobbing down on the hill happens later on the return journey.

Post edited at 10:42
OP Robert Durran 04 Jul 2020
In reply to DancingOnRock:

> So huge long walks or lots of short walks, or basically not sitting around, would always be better than smashing yourself out and then sitting around all day.

During lockdown I have actually been doing lots of formal exercise, possibly more distance and height gain per week than normal. The difference is that my job (teaching) went from pretty active with lots of time on my feet to sedentary, and evening wall sessions disappeared. I've been eating about the same. So it would seem to suggest that the sedentary stuff has been surprisingly influential!

OP Robert Durran 04 Jul 2020
In reply to DancingOnRock:

> You’re bobbing up on the flat and uphill, just the bobbing down bit on the flat doesn’t use any energy and all the bobbing down on the hill happens later on the return journey.

Yes, so the total energy used bobbing is greater on a flat rather than a hilly route of the same distance. Unless it's steep enough to use higher steps than one's natural bob height!

Post edited at 10:55
 Jamie Wakeham 04 Jul 2020
In reply to Robert Durran:

> Though, the "bobbing" will be almost entirely in my legs whereas going uphill I am lifting my whole body's mass.

It's an interesting exercise to walk alongside a whiteboard, holding a pen out at shoulder height, to see where your CoM is going.  Some have a really smooth walking gait and their CoM hardly moves (in which case using the approximation that you're only lifting your legs' mass is a good way to work things out).  Others clearly lift their entire body as they walk.

As soon as you start jogging it becomes clear that you really are lifting your whole CoM by a few cm on every stride.

Removed User 04 Jul 2020
In reply to Robert Durran:

Not entirely relevant but in an early SMC journal someone reported that when ascending Ben Nevis a person would generate about 2/3 horsepower which would be about 500 watts.

If we're about 25% efficient then we're burning 2KW of energy when walking uphill.

 bouldery bits 04 Jul 2020
In reply to Robert Durran:

I don't think there is a hard and fast answer here.It depends on a huge variety of factors including, buy not exclusive to:

Biomechanics

Metabolic effeciency (Which does fluctuate and change)

Gut biome

Weather conditions / temperature

Terrain

Footwear

Equipment

Calorie source

Training history (the more endurance trained you are, the fewer calories you will need to do the same work)

Mental state

I tend to work on the basis that I can't work out the specific calorie offset with any real accuracy so, when losing weight, I simply eat less and do more to create a deficit. 

 petemeads 04 Jul 2020
In reply to Removed User:

The people who can win the Nevis race can probably hold 500 watts for the hour or so it takes to ascend, pro cyclists can manage that sort of power, but the man in the street would not get near that - power is how quickly you can use energy and normal humans are not that energetic!. Yes to the racer using 2kWh+ of energy during the race. 2kW is a rate, not a quantity of energy.

Edit: But the Potential Energy component for the slower walker is identical, mass x height gain, so the overall energy use will be similar, just spread over a longer period.

Post edited at 14:12

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