Walking uphill is harder than walking on level ground. You use more energy and you burn more calories.
That is intuitively obvious, but we have not had a good way of putting numbers on it that include factors such as: How steep is the incline? How much do you weigh (including the backpack you’re carrying)? How long is the hike?
What may not be as obvious is that walking downhill is easier at first, until it is not, as anyone who has walked down a long, steep mountain slope discovers. The precise relationship between how fast you walk, how steep your trail is, and how much energy you burn has been the focus of researchers at the United States Army Research Institute of Environmental Medicine. They have developed a mathematical formula that captures these variables.
The Hiking Calculator
The details are published in Medicine & Science in Sports & Exercise, but the formula has been captured in a fun, easy-to-use calculator at https://jscalc.io/calc/yFvvpeAfQ9lPBnGU
I tested the calculator. I have done hundreds of uphill hikes, including extended adventures well over ten hours in duration. I would notice that on the longer forays, I would return home having lost 2 – 3 pounds in the one outing! That was not due to water weight loss: I hydrate frequently, and on a hike or climb of that duration I’ll easily consume 2 – 3 liters of water.
So, what does the calculator say? If I put in my weight (178 pounds) plus pack weight (18 pounds for a day climb) and if my average up/down speed is 2 MPH, then I estimate the average steepness grade. Of course, that is highly variable during any hilly hike which could range anywhere from 10% to tough sections of 50%+. For an average of 20% grade and a ten-hour hike, the calculator says I would burn 729 calories/hour or 7290 calories total.
At 3500 calories equaling one pound of body weight, the calculator predicts I would lose a little over two pounds on that hike. That matches perfectly with my actual experience.
Curious about how that compares with a level walk for ten-hours? Just put zero for grade in the calculator. The answer is 264 calories per hour, 2640 calories over the ten hours or a loss of about 3/4ths of a pound.
Hilly Hiking – Losing Weight, Gaining Fitness
Hiking on a 20% grade burns almost three times the calories of a level walk.
The calculator and its underlying formula also tell us that when we head uphill, our energy expenditure is directly proportional to the steepness of the grade. Going downhill, in contrast, the energy expenditure initially decreases, but at grades of about -10 percent it reaches a minimum then starts to increase again.
Interestingly, the calculator shows calories burned per mile as well as per hour. Here we learn that the number of calories it takes to cover a mile is somewhat constant. If you go slow, your rate of energy burn decreases but it takes longer to cover a mile; if you go fast, you’re sizzling through calories, but you finish sooner. Between about 2 and 4 miles per hour, which encompasses most people’s comfortable walking paces, those two factors roughly balance each other and calories per mile stays pretty flat.
Measuring Hiking Difficulty
The calculator also serves as a way of getting a rough estimate of the relative difficulty of hiking different slopes. For example, the horizontal line on the graph above tells me that if I’m used to hiking at four miles per hour on level ground, it will take a similar amount of effort to go two miles per hour up a 10 percent slope. If you want to play around with some of these parameters yourself, try plugging some numbers into the calculator.
The horizontal black line in the chart shouldn’t be taken to suggest that keeping your energy expenditure constant over hilly terrain is optimal. I find that I push harder on uphills and relax a bit more on downhills. That is why I hardly talk on uphills, but I turn into a real jabber mouth on downhills, although part of that is the knowledge that whatever I was summiting already happened.
Have fun with the calculator and have even more fun on a real hike!
Calculating an Incident from the Book
Here is what I learned from the calculator about a crucial incident in the book:
Hiking at my current weight with an 18-pound pack at 2 mph on a 10% uphill grade burns 480 calories/hour or 240 calories per mile. The amount of calories burned goes up 18% if my pack and I are 35 pounds heavier. For my first backpacking climb in the book, The Dog Who Took Me Up A Mountain, I was 25 pounds heavier and I had a pack that weighed 10 pounds more than it needed to.
Read more about that hike in the book!