Using (.3 x weight) for net calories walking...

WalkingAlong
WalkingAlong Posts: 4,926 Member
in Fitness and Exercise
That .3 has never sounded right to me, for myself anyway. I know this is the article it comes from:

http://www.runnersworld.com/weight-loss/how-many-calories-are-you-really-burning?page=single

And this is the source it lists:
http://web.stanford.edu/~clint/Run_Walk2004a.rtf

The source doesn't discuss it in such terms so someone has extrapolated something, as far as I can tell. The source study does say it used 24 subjects with a mean age of like 22, sounds like none overweight. And converting kj to calorie and meters to miles, it sounds like they found 115 calories burned per mile running vs. 81 for walking. That all sounds right to me.

But how did Runners World arrive at the 'gross to net' difference for walking of of .23 (as in .53 minus .3)? The table in the article implies each of our BMR is around .23 times our weight, for the time spent walking a mile. Just inputting my own data, that would imply at 3mph, I would burn .23 X 155 = 36 calories in 20 minutes (time to cover a mile at 3mph). My BMR is about half that, though. So my gross and net burn would be much closer than they suggest. The multiplier for 'net walking' that would make sense for me wouldn't be .3 x weight, it would be around .42. That may not seem like much but it makes my walking net burn almost 50% higher than the .3 formula.

So I'm thinking maybe the .3 only applies to people whose BMR is roughly (.23 x weight in lbs.) for the time it takes them to walk a mile. So assuming 3mph, it would imply a BMR of 16.56 times your weight in lbs. Is anyone's BMR 16 times your weight?

Replies

  • junlex123
    junlex123 Posts: 81 Member
    Yeah, does seem to be some fudging going on in that net calories formula.

    My BMR's around 1600 as a 179cm/68kg male according to most calculators (and empirically this seems to be in the right ballpark at least).

    So in 15 minutes I'd burn ~17 cal doing nothing, in 20 minutes I'd burn ~22.

    Using the gross walking calculation of 0.53 x weight/mile I'd burn 79 cal walking a mile.

    So at 4 mph burn a net of ~62 cal per mile, at 3 mph ~ 57 cal per mile.

    Or at 4 mph my net burn calc would be ~0.41 x my weight/mile, at 3mph it'd be ~0.38 x my weight/mile, very similar to yours.
  • WalkingAlong
    WalkingAlong Posts: 4,926 Member
    Thanks for looking at it. You're 29 and male so it's not my advanced age of 49 or female-ness. Our weights are similar.

    I'm thinking for someone obese, it would be even more wrong, right? It would imply a 300lb. person had a BMR of nearly 5000 calories a day.

    I don't think anyone has a BMR that's 16 times their weight in pounds.
  • junlex123
    junlex123 Posts: 81 Member
    Yeah, pretty sure the author of the article pulled that adjustment out of his own imagination, numbers only start to approach making sense at 2 mph or so. At 2 mph my net burn calc would be 0.30 x my weight/mile, so my bmr adjustment would be his 0.23 x weight/mile. His adjustment doesn't take proper account of how a faster pace means a shorter period of basal metabolism to subtract.

    Edit: assuming the gross numbers are correct in the first place and widely generalisable, and the author's not fudged something else when trying to extrapolate from the paper's results (not looked closely enough to confirm yet), the correct adjustment would be:

    Net calories per mile for running: (0.75 x weight in lb) - (BMR / 24 * speed in mph)
    Net calories per mile for walking: (0.53 x weight in lb) - (BMR / 24 * speed in mph)
  • WalkingAlong
    WalkingAlong Posts: 4,926 Member
    junlex- You have made my day. It took me a minute to follow but I think you're right. :love:

    To avoid confusion I might write it as:

    Net calories per mile for walking: (0.53 x weight in lb) - [BMR / (24 * speed in mph)]

    Then again, if I run my numbers through the Compendium METs values, it's got me back down to the 50 calories per mile net (at 155 lbs., 3mph) which isn't much higher than the .3 estimate (46 calories). Though their gross estimate is 70 for me vs. 82 for the Runner's World formula.

    https://sites.google.com/site/compendiumofphysicalactivities/Activity-Categories/walking

    Just to add another estimator- Fitbit gives me around 100 gross or 80 net.

    I guess the estimates are close enough for someone in the normal weight/speed range. I wonder about the obese.
  • junlex123
    junlex123 Posts: 81 Member
    Oops, yeah missed out that second set of parentheses.

    From a purely physics point of view, the amount of energy required ought to scale linearly with a person's mass, but that's the kind of generalisation that led to the misconception of a mile requiring a set amount of calories regardless of running or walking in the first place. It's conceivable that a much heavier or slower person's gait would be significantly different in bio-mechanical terms rendering the generalisation for gross calories/mile very inaccurate - walking at 2 mph there's a lot less bounce in my movement compared to 4 mph: a lot less leg flexion, very little arm involvement, so I'd imagine it's energetically more efficient per unit of distance. Conversely moving a lot more mass with musculature that is not proportionately more powerful might result in a less energetically efficient gait.

    Interesting to think about but yeah, think the estimates are usually close enough that the errors aren't going to have too big an impact in most cases.

    Edit: if you really want to nerd out on this can chase up some of the studies referenced in http://en.wikipedia.org/wiki/Preferred_walking_speed ;) - http://jap.physiology.org/content/100/2/390 deals with obesity and gender in particular for ex.
  • WalkingAlong
    WalkingAlong Posts: 4,926 Member
    I will check it out. It is interesting to consider. I think my Fitbit might be estimating me at higher than the METs value for the speed I walk (and I'm pretty sure they do use METs) because I bet I move more than the typical person my size moving at that speed. I'm not very graceful. Which should imply I burn more, though, and I did lose weight at the pace that Fitbit estimated I should over a year that I tracked it all closely there.

    The source study for the Runner's World article did mention that women burned significantly less than men due to having less fat-free mass. The article formulas don't take that into account.

    "On the treadmill, the males expended 520.6 ± 27.6 kJ for 1600 m; this was significantly higher (P < 0.05) than the energy expenditure by the females (441.1 ± 25.6 kJ). For the walk, the males expended 370.4 ± 17.7 kJ, and the females expended 309.6 ± 17.2 kJ for 1600 m (P < 0.05 between genders). When energy expenditure was adjusted for fat-free mass, the gender effect disappeared, but running exercise still required more energy than walking (P < 0.01; Fig. 1b)."
  • Mr_Knight
    Mr_Knight Posts: 9,532 Member
    So in 15 minutes I'd burn ~17 cal doing nothing, in 20 minutes I'd burn ~22.

    ...

    So at 4 mph burn a net of ~62 cal per mile, at 3 mph ~ 57 cal per mile.

    This is consistent with MET as well, which has 3.5 for 3mph (17 * 3.5 -> 59 cal).

    There are differences between walking 2.5mph and 4mph, but unless the distance is very long that difference is lost in the noise and it's just easier and less confusing to use an average value. Heck, the error in the BMR/RMR measurement is going to swamp any difference.

    It'll break down at racing speeds, but anybody walking at racing speeds is unlikely to be on MFP looking for caloric advice. :drinker:

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