Calories: Determining Calories Expenditure Hiking

Well there are many calculators out there that will determine the calories expenditure whilst hiking, backpacking, etc, I find they are limited and often never give you any indication as to how they come up with their numbers. Well probing a little further I did manage to find tables here http://www.nutribase.com/exercala.htm . Although I find these can give us some idea, there are somewhat limited concerning pack size. What we can divulge from these is that there are two variables concerning calorie expenditure: pack weight, and the persons weight.

If we try to take a 110lb person with no pack (ie walking or hiking), and a 100lb person with a 10lb pack you will notice that the counts are not the same. You can try this with any combination.

The Twofold Problem

We need to figure out the rate of expenditure of calories, and the rate of how pack weight changes this. To figure this out we need to use old school quadratic equations, which is made much simpler by using a spreadsheet program. Without going hardcore into disseminating this data we arrive with two separate equations:

Increase of Cal Expenditure based on Pack Weight = 0.29 x (Pack Weight) +14.9
Calorie Expenditure of Person = 1.55 x (Persons Weight) + 0.25

Person A is carrying a 30lb pack, therefore their expenditure has increased by 23.6 Cal/30 min. If we look at the data we notice that it increases by 24 cal per weight group, close enough. Likewise if Person A is 175 lb carrying no pack we know that 271.5 cal/30 min is the expenditure, which is also very much in line with our data.

If we figure out the equations for we will notice that the slope of each group is equal to the result given by our equation for the increase in pack weight. Therefore if we can combine the two equations we can figure out any calorie expenditure at any weight, carrying any size pack. If you try this you may notice that your result will be a decimal point off, and in addition any answer will be per 30 min (this is not necessarily a bad thing, and the equation could be adjusted, but I think it provides for more accurate planning.)

The Equation

Calories Expended per 30 min =(Pack Adjustment x 0.1) (Persons Weight)
Pack Adjustment = 0.29 x (Pack Weight) + 14.9

or

Cal Exp / 30 min = ((0.29 (Pack Weight) +14.9) 0.1) x Persons Weight
Cal Exp / hour = (((0.29 (Pack Weight) +14.9) 0.1) x Persons Weight) x 2
 
Person A weights 170lb carrying a 30lb pack.

Cal Exp / 30 min     =  ((0.29 (30) +14.9) 0.1) x 170
                               =  ((8.7 +14.9) 0.1) x 170
                               =  ((23.6) 0.1) x 170
                               =   2.36 x 170
                               =  401.2

If we compare 401.2 cal/30min with our table we see the table has 399. Not perfect but more then good enough for our purposes.

Conclusion

It is now possible based on this information to get a more accurate idea of your calorie expenditure. We can also now figure out diminishing results (ie carrying this much food is actually causing me to burn more calories then its providing), and properly plan. It should be noted however that any pack sizes greater then 30lb is purely speculative and based on previous data. Next I hope to be able to figure out this equation using a range of activities.