Years and seasons pass but hiking is still as popular as it's ever been. We tend to do a little hiking to stay fit, spend time with our loved ones, meet new folks and explore the natural beauty of our planet. If we can't find time during the week to jog, play squash or even bike to work, we even treat those little hiking retreats as a chance to lose a bit of weight. And it's definitely a good thing. Calculating calories burned during various kind of activities is a fairly simple matter as it revolves around the following equation:
Calories Burned = MET * Weight (kg) * Time (hrs)
MET, short for Metabolic Equivalent, is the amount of oxygen used for particular activities, such as running, walking up the stairs or cycling. Most common values you can find here. As an example, person weighing 70kg (154lbs) who jogs for an hour will burn approximately 70 * 7 * 1 = 490 calories. Although this result is only approximate, it can serve as a good starting point for our further calculations.
Back in 2002 a group of researchers published a paper in Journal of Applied Physiology entitled "Energy cost of walking and running at extreme uphill and downhill slopes". They put a group of volunteers on a treadmill and started testing how much oxygen they use at different gradients, starting from the flat walk or run and climbing higher and higher. After a thorough research they were able to determine how the slope of a hill or mountain affects the amount of oxygen used and, as a result, energy consumed. Having calculated that, they were able to come up with the equation which roughly allows to compare calories burned on a walk and a hike. From there, it was only a short way to use the aforementioned equation and calculate the energy levels for both climbing up and down.
We took the inspiration for this calculator from the very similar tool published several years ago on Hiking Science blog. And it goes like this - to get started enter the length of your trail as well as its elevation gain (the sum of every elevation hiked during the trail). This information should be available online as well as at the trail itself. Then add your body weight and your backpack's weight (skip if you're not taking one). Once you have those 4 numbers filled, all calculations will be performed and you'll see your approximate results.
Let's discuss a simple example to make things clear. Mark went on a hike last weekend which lasted for 12 miles (19,3km) and featured 2500 ft (762m) elevation gain. Mark is pretty slim himself, weighing 150 pounds (68kg) and carrying 18 pounds (8.15kg) of backpack on his back. As you can see, trail averaged around 7.89% grade. Below you can see what the way up and down would correspond to on flat terrain - to burn the same amount of calories Mark would have to walk 10.394 miles for the way up and 6 miles for the way down. In total it would result in 16.394 miles walked.
Now that we have those numbers, we can calculate the amount of calories burned on the way up and down. First, if Mark were to leave his backpack before the trail start, he would burn roughly 923 calories for the way up and 532 for the way down. In total - 1456 calories. Add the backpack and the numbers go up - 1005 for going up and 580 down. In total, Mark should expect to burn around 1585 calories during his hike.
Now, keep note that we based those formulas on a research done in a lab and not on a mountain slope. This means many outside factors were not taken into consideration such as Mark's stamina and individual predispositions, weather conditions, trail structure and speed of hike. Unfortunately, we simply don't have the sufficient amount of data so can only offer approximate values. Regardless, it should work as an interesting way to check the calories needed for each trail and could help hikers better prepare for their trips. Use the tool responsibly and don't forget to take some water and food with you, even if you're headed just for a short walk. Best of luck!