Thank you for sending us an email! We're going to post it here in the community so other folks can read it and potentially weigh in:
Thanks for responding to my post. Much appreciated.
Yes, we’re talking about calories as a measure of energy burned during a workout. The underlying objective is to assess the approximate daily calorie intake I need pulling a sled for 20-25km a day. Excluding rest stops, this works out at around 5 hours/day pulling (5km/hr or 3mph/hr). I should stress that there are so many variables - body weight, pack and ski weight, sled weight and friction resistance, distance, ascent, descent, speed, terrain difficulty, temperature and altitude to name a few – that a rule of thumb of 10,000kj per day (500g of food averaging 2,000kj/100gm) plus extra energy bars is probably the wisest approach! It’s not as though there’ll be a convenience store on route to top up supplies!
So, to come back to the objective and a method to make a pre-assessment of the energy requirement based on the closest activity to mimic pulling a sled, namely tyre pulling. If I was attempting the expedition on a fat bike I could calculate energy expenditure quite accurately using a pedal power meter. At the other end of the scale, if there’s no exertion-related data available from my body, my gps device is left to calculate energy expenditure based on the raw metrics including time, distance, age, weight, and activity level. Since this method doesn’t take into consideration my effort level ascending or descending, headwind or tailwind, etc, the number of calories burned is only generic.
That brings me to your suggestion – heart rate. According to the sports coaches and nutritionists, most of the HR-based calculations are within 10-20% accuracy. Some of the algorithms used in HR devices are very sophisticated. The more advanced methods evaluate beat to beat to estimate MET (Metabolic Equivalent) which is used to determine actual work expenditure. Some devices apparently have a learn function that with continued use tracks changes in fitness and adjusts the energy algorithm.
Wearing a strap around my chest while pulling a sled up and down paths in my local park seems to be a reliable method to measure calories expended even with the HR calculation algorithm being ± 10-20% accurate based on comparisons performed by cyclists using HR data and power meters. Even so I may still rely on a rule of thumb!
All the best, Robert