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Here's some Strava stats from a walk I just took after lunch:

3.3km, 34:14 moving time, 10:18 /km, Calories 289

Admittedly, I'm a fast walker. But 289 calories seems to be way over the top for a 3.3km walk. (Isn't the rule-of-thumb "100 calories per mile" for running?) If it's correct, I probably have already burned away most of what I ate for lunch.

Question: Is Strava overestimating my calories burned from walking?

Since I'm attempting to use this app to assist in weight loss, an underestimation would be more helpful to me.

I'm running the app from my mobile phone. I'm currently 70kg (hopefully not for much longer).

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Yes, given your weight and pace I'd expect a value below 150 Kcal. A way to confirm this would be to plug your details into a couple of the common Kcal estimation equations and take an average eg.

The ACSM and MET formula:

ACSM Kcal/Min ~= 0.0005 * bodyMassKg * metersWalkedInAMin + 0.0035
              ~= 0.0005 * 70 * 96 + 0.0035
              ~= 3.3635 Kcal/Min
              ~= 115 Kcal in 34.25 min / 3.3Km

MET Kcal      ~= METS   * bodyMassKg * timePerformingHours
              ~= 5.0    * 70         * 0.25
              ~= 87.5 Kcal/Mile
              ~= 180 in 3.3Km

    where METS = 5.0 (walking, 4.0 mph, level, firm surface, very brisk pace)

Average: (180 + 115) / 2 = 147.5 Kcal in 3.3Km

As your fitness level is a significant factor in how much energy your body needs to perform a task, an even better way to confirm the accuracy of the Strava calculation would be to capture your heart rate after a mile, one of the free apps that uses your phone's camera, to measure the pulse in a finger should suffice, or just fall back on simply taking your pulse. Then at your leisure plug your heart rate, the split time to walk the mile, and a few vitals into the Rockport Walking test formula, to obtain an estimated VO2max score (fitness assessment score):

Estimated VO2Max = 132.853 - (0.0769 * WeightLbs) - (0.3877 * AgeYears) + (6.315 * isMale) - (3.2649 * TimeMinDecimal) - (0.1565 × HeartRateBPM)

Where:

  • isMale: Male = 1, Female = 0
  • Time to walk mile is expressed in minutes and 100ths of minutes

There are sites / apps that will do this for you eg. Heart Rate Based Calorie Burn Calculator, BioMetrIcs. As well as providing the summary Kcal for your activity.

Kcal/Min ~= 5 * massKg * VO2 / 1000

where:

VO2 = (currentHeartRate / MaxHeartRate) * VO2Max

MaxHeartRate ~= 210 - (0.8 * ageYears)

Note: There have been a few studies around that assessed the accuracy of the tracker apps eg. Why your fitness tracker could be a waste of money: New research shows the must-have gadgets are often wildly inaccurate by as much as 40 PER CENT

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Yeah, that seems like a lot, I'm 90kg and I would question such a number for myself! Try some online calculators and see what value they give you, the ones I tried gave a number around 200 kcal. Using these calculators is tricky because you don't know wether they give you the total number of calories burned or the amount of extra calories burned above your basal metabolism (which is around 80 kcal/hour)

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