Off the Beaten Path in the Colorado Rockies
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Here is a Colorado front-range example. This goat was attracted to his pose by peeing while they were watching me. An intrepid goat is always willing to risk walking near me for such a treat.
My contribution to the goat photos, from 20+ years ago. My dog couldn’t believe they were walking right up to her, and I had to leash her.
My contribution to the “Goats waiting for me to pee in the Weiminuche” school of outdoor photography.
More goats. Mount Massive saddle 14K July ’24. Everyone carefully backed up as momma and baby casually walked by.
@Ryan I’m fascinated by calorie estimations as they’re a far bigger opportunity to save weight than any individual piece of gear would be.
I’ve been estimating calories with a slightly different approach and getting good results (estimated weight loss = real weight loss), but the method comes up with some very different outcomes than Ryan’s way of doing it.
Ryan and I both start with the same base calories using a BMR formula.
Ryan then estimates 100kcal/mile then adds extra miles based on the difficulty using Petzoldt (add 2miles/1000 ft elevation). He then adjusts the added miles based on steepness & obstacles where multiplier could be as high as 3.3/1000feet (based on his 4.3 difficulty factor)
My method uses a different approach. I start with Petzoldt, to add 2miles/1000 ft elevation. It then adjusts the calorie requirement using “PAL”, Physical Activity Level, a multiplier for BMR taken from here which increases as total energy miles increase.  Assuming a mid-weight unloaded backpacker on flat ground but increasing distance for Petzoldt:
Using this study which validated Petzoldt and which Ryan referenced in one of his old articles, loaded with a 44.5lb pack requires ~ 29% more calories than unloaded (Table 3). But the study also found that calorie burn depended on total skin out weight, not carried weight. So adjusting the unloaded PAL for a 155lb hiker carrying a 30lbs pack, the loaded PAL becomes:
Now comparing the PAL method to Ryan’s method, the calorie count is very different as difficulty increases. These are two single day use cases within longer trips where I counted calories and monitored weight gain and found my results very accurate. And this is assuming 2.0 Petzoldt multiplier for Ryan’s method, not the adjusted 3.3 for really hard days where Ryan would now estimate even more calories are needed.
Ryan’s finding with HRM validates that is more accurate than either of these back of envelope calculations. While it’s true HRM is a good estimator of calorie burn, the accuracy of the watch HRM can vary significantly and needs to be considered as well:
So why are PAL method and Ryan’s old (not HRM) method so different? Â Especially given both Ryan and I get good estimates of weight loss that track with field outcomes?
Dunno.
I suspect some of it is that these really hard days or really easy days are outliers and we don’t do enough of them repeatedly to collect stats to deduce which method is most accurate. I also don’t know if Ryan accounts for water loss. I give it a couple days after the trip before weighing myself, while not over eating on those days, because my water weight is artificially low.
Santa gave me a Garmin watch for Christmas and I’m going to start using it to track calories with the HRM. And given some free time, I plan to review the studies looking for clues.
I love this nerdy stuff, so I revisited the “The Validity of Petzoldt’s Energy Mile Theory ” study, which measures caloric burn with live subjects.
Some interesting outcomes from the study:
- The weight of the pack doesn’t have a huge impact on calories burned, but the impact increases the lighter the hiker and heavier the pack (as expected). For example, a 15lb pack reduces caloric burn by ~ 4% for a 155lb hiker compared to a 30lb pack
- The extra coloric burn from the added pack weight was the same on flat ground as on a 9.5% grade, when expressed as a percentage. In absolute terms, more calories are burned per km by the added weight in 9.5% grade vs flat ground because the burn rate is higher
I rethought my penalty for the pack weight and realized it should only apply to the excess calories burned from the exertion of the hike, not to the base burn rate (BMR). Readjusting:
The standard deviations of the outcomes in the study are significant and actual calories burned will vary notably with individual, just as Ryan’s 100kcal/mile assumption will vary person to person.
What I’ve done for my trips is to customize the PAL-vs-km table based on real data from my trips. If using Ryan’s method, it will probably result in more consistent and repeatable outcomes by adjusting both the 100kcal assumption and the route difficulty rating using personalized results.
I chose 4.8kph to 6.4kph data for the PAL method since that’s the speed range I move at on flat ground. Faster or slower hiking will adjust PAL up or down accordingly, similar to how Ryan adjusted his multiplier for hard scrambling.
This may seem like excessive hand wringing but using this approach I’ve been able to drop pounds off my food carry for even just week long trips.
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