Formula for determining kJ burned bushwalking

[Mutley]

At the risk of regurgitating (food pun) any previous threads, I have been trolling the inter web for a few hours, and can't seem to find a reliable way to calculate KJ burned bushwalking.

There are plenty of simple calculators, but I really would like a formula to use in a spreadsheet, in which I enter the total body weight, pack weight, distance, ascent, descent, speed and even a factor for terrain difficulty, temperature and altitude. I am planning a solo AAWT trip in December and think correct KJ intake is critical. I want to try to save as much weight as possible, but don't want to finish the trip looking like a dehydrated greyhound.

[icefest]

I'm sorry but it's not actually that simple. Even if you find a detailed formula there are too many independent variables (eg: leg/thigh ratios, type 2a/b muscle fibre ratios, mitochondrial efficiency, carrying extra water).

If not coming back looking like a dehydrated greyhound is your aim then your best bet is to plan for 3000-4000cal/day on big walking days, and have enough extra snacks/oil/butter in your food drops that you can just eat more when you realise that you have started losing weight.

In you are planning on walking the entire AAWT in 1 month then I doubt you will have enough time to eat and digest the energy that you will need to burn.

[Mutley]

I'm sorry but it's not actually that simple. Even if you find a detailed formula there are too many independent variables (eg: leg/thigh ratios, type 2a/b muscle fibre ratios, mitochondrial efficiency, carrying extra water).

If not coming back looking like a dehydrated greyhound is your aim then your best bet is to plan for 3000-4000cal/day on big walking days, and have enough extra snacks/oil/butter in your food drops that you can just eat more when you realise that you have started losing weight.

In you are planning on walking the entire AAWT in 1 month then I doubt you will have enough time to eat and digest the energy that you will need to burn.

Yep, it is complex. I have found some formulas based on effort measured by VO, then calories burned from there. It will vary according to a thousand factors, including fitness, efficiency of muscles etc. But I am a self confessed spreadsheet junkie and would really like to have an estimation tool, to calculate how many kj I allow. For the AAWT I'm guessing 13000 kj per day. At this stage I'm planning 32 days plus 3 rest days. This is walking an average of 8 hours a day.

[nq111]

I expect icefest is spot on and that there are too many individual, climatic and terrain variables to get a worthwhile improvement in accuracy without a whole heap of specialised investigations (if you are Usain Bolt I am sure all those investigations would be done). Just because you may be able to calculate 17,459.3kj for day 15, doesn't mean it is more useful than a good rule of thumb if the input assumptions can't be made accurate.

For what it is worth I budget to carry minimum 15,000kj per day (700g of food averaging 2,200kj/100gm) and lose a little weight on that - of course you may vary, and vary more than just a little bit. That is ok, as I am only gone a week or so. I read somewhere it is pretty easy to exceed 18,000kj per day carrying a pack in the mountains. From memory I think Andrew Skurka has some good practical advice on energy budgeting for long trips published somewhere.

[Moondog55]

Part of the "Trick' is to stash as many calories and as much protein as possible into the food dump for use at that point in time, so when you reach the food dump you gorge yourself for 1 or 2 meals to replace some of the body fat you used as fuel in the previous week, another reason I personally think rest days are important in long walks.
My own experience tells me that I overestimate the amount of food I need in the first week and underestimate for weeks 2 and 3 and that's as long as I have made trips for and that was quite a while ago when I was fitter and stronger

[Onestepmore]

When I read the title, my first thought (as I sit here in my favorite cafe sipping a cuppuchino on a wet Sunday morning) was 'why' and then to hubby 'not possible'. As the others have said there are just way too many variables - terrain, weather, detours, can all make your carefully calculated kilojoules change. My feeling is that if you're going to try and plan to that degree, you're going to be let down. Use the rough guides above (I think all these guys have done multiday walks) of per day requirements of high calorie dense, but slow burning nutritious food, and take some extra for contingency plans, and you should be right.
Disclaimer, I've not done any long walks, so may be talking through my a#%*, but I'm just looking at this from a common sense perspective. I know when I over plan, things go pear shaped, due to things I can't control.
As an aside, I've recently read a few books on Appalacian Trail through hikes. How do these people survive for months on a diet of Pop Tarts, peanut butter, trail bars and pizza?

[Mark F]

Oh to look like a dehydrated greyhound at the end of a trip!

I agree with Moondog, Week 1, especially days 2 and 3, I tend to eat less (mainly at lunch), with the quantity increasing the longer the trip. I am usually working on 10,000 - 12,000 kj in my planning (I averaged about 20km per day on the AAWT - Tharwa to Hotham) but have extras in my food drops for immediate consumption. My food drops include fruit juice and foods that are not dehydrated.

I find it really important to have a wide variety of foods you like. You can get very sick of a unvarying diet and end up eating less as a result. I also take a multi-vitamin each day just to handle any deficiencies in the diet.

[Mutley]

Thanks everyone for the input. Did the Larapinta last year and found I actually lost weight on 12500 per day. So for any calculation to be considered useful, it should give me about 14000 kj a day for the AAWT. I'm just really curious to see if any physics student out there has done the math. We can very accurately predict kj burned at rest, using various methods. So to allow for terrain, temperature, weight carried, distance walked should be straightforward. There are many apps which estimate calories burned walking, cycling etc, based on altitude change, speed and distance. This is just based on algorithms within the apps. Yes, they are estimates and it doesn't take into account fitness level, metabolism etc. but they are still a good indication of energy expenditure. Cheers..

[icefest]

We can very accurately predict kj burned at rest, using various methods.

Are you sure? AFAIR there are variations of over 10%.

Not even measuring oxygen consumption can tell you how much energy your are using.

How do these people survive for months on a diet of Pop Tarts, peanut butter, trail bars and pizza?

It might be age/being male, but I wouldn't have a problem with that diet.

Day 6 in a cold winter hike I start imagining how tasty butter rolled in brown sugar would be.

[nq111]

I think the math would be the easy part. Even it is 100% accurate - it is the variables and assumptions where I think this idea would fall apart.

Stupid in = stupid out, even with the best algorithms in the world.

[Mutley]

http://hikingscience.blogspot.com.au/p/ ... ed_22.html

[icefest]

I think that one is based upon walking on a treadmill - once more, so many variables that you cannot control for.

You'll need spare food in your caches anyway, in case you lose a day due to bad weather, you might as well just pack a bit extra.
If you are all too worried about losing weight, eat an extra 4000 kj a day for the preceding month so you'll just lose the weight that you gained.