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HRM and calories burned (cross-post from Fitness board)(8 posts)

HRM and calories burned (cross-post from Fitness board)mleptuck
Jan 14, 2003 4:17 AM
(Cross-posted from Fitness board, thought I'd get more views here)

I'm fairly new to road biking (started in earnest back in May, and am completely hooked). Anyway, to combat my annual winter bulk-up (cold-weather gear is REALLY expensive!) and get a head start on the Spring, I recently got an indoor trainer and a Polar A5 HRM to get myself back on the road to semi-fitness.

I just got the A5 today and went for a spin in my basement to try it out after work. I saw some 'interesting' numbers, and wanted to know if they are believable, since the calories burned value seems quite high.

I'm a big guy (6'3", and going at about 240# now, though I was riding around 225# over the summer), and am 32 years old. I programmed the A5 with all the relevant data, and set out on a ride while watching some TV.

I was in 53x19, with a reasonable level of resistance on the trainer, and kept an average cadence of 86RPM over 34 minutes.

I came up with avg. HR of 164 (believable, since my 85% upper limit is 160, and the alarm was sounding nearly the whole time), and I only spent 6 minutes in the 60-85% zone. (As an aside, using the 220-age, my max HR is 188. I had my doc do a Bruce stress test a couple of months ago and hit a max HR of 199 so I do think I need to manually set my HR ranges higher on the monitor).

Now, the monitor tells me it believes I burned 751 calories in this 34 minutes. Can this be anywhere near accurate? It seems awfully high to me. I'm having a hard time finding definitive formulae on the web for computing this on my own.

Any one? Thanks!
-Michael
Too high.OldEdScott
Jan 14, 2003 6:04 AM
In my experience, HRM calories-burned functions are awfully optimistic. As someone with lifelong difficulty keeping weight off, I've counted calories in/calories out for 30 years or more, and I can probably calculate +/- 100 how many calories I will burn, on average, given a set of daily activities.

One winter, just for grins, I used the calories function of my Cardiosport Club -- kept track of what it said I burned over a three month period on the trainer. By its calculations, I should have lost three pounds. In fact, I gained two.

Through various figurings and jiggling of numbers, I concluded that the Cardiosport figures credits about twice as many calories burned as actually burned -- although I can't tell from their literature whether their number include calories burned from just basal metabolism during the period of exercise, i.e. the 'base'calories you burn simply from being alive. I suspect it does. That would jack the number up somewhat, about 120 calories an hour in your case. But still ...

Anyway, the bottom line is: Big grain of salt. It's at best a rough estimate, at worst sheer fantasy.
Too high.mleptuck
Jan 14, 2003 6:25 AM
So would I take it that 450-500 calories burned in a roughly half-hour spin is a more realistic figure?

There is just a ton of conflicting and seemingly inaccurate data on the web pertaining to this. Makes it hard to get a true method for gauging my progress.
Still too high.OldEdScott
Jan 14, 2003 7:21 AM
I think if you're cranking pretty good at the HR you mention for 1/2 hour, at your weight you MIGHT burn 200 extra calories above and beyond your basal metabolic calories. Depends on a lot of factors. I weight 190, and I estimate I burn about 300 AN HOUR on the trainer. Remember, we're talking 'extra' calories here, the ones you burn by virtue of exercising.
Still too high.mleptuck
Jan 14, 2003 7:35 AM
Yea, I hear you, but I'd like to know how I can actually determine this figure through some mathematical computations.

Do you know if any formulae which might help me?
Too many variablesOldEdScott
Jan 14, 2003 8:00 AM
for there to be a mathmatical formula. The only way I know of to be fairly accurate is to monitor weight, calorie consumption and exercise over a substantial period of time. It's complicated and anal, and probably more trouble to you than it's worth. But I've fought this battle for decades, so it's second nature to me.

For example, just using easy figures to deal with:

Say I weigh 200 pounds. Say I know for a fact, from keeping daily records, that my average calorie intake is 3000 a day, and that that figure maintains me at a steady 200 lbs.

Say I begin an exercise program, one hour a day on the bike, six days a week. I continue to average 3000 calories a day. My activities remain the same EXCEPT for the bike riding.

Say three months later I have lost 5 pounds. Since each pound represents 3500 calories that I burned in excess of the food I ate, the 5 pounds represents a total of 17,500 calories.

OK, in the three months of bike riding, I rode 78 times, a total of 78 hours.

If I divide the 17,500 calories burned but didn't eat by 78, I find I am burning 225 calories an hour in excess of what I would burn if I didn't ride. So I can be fairly confident that an hour's bike ride, for me, burns something like 200-250 calories.

Calories expenditure really can't be known any other way, since everyone's metabolism is different, rates of exertion are different (an hour for you is different than an hour for me, terrain varies, wind varies). Also, as you lose weight you will burn fewer calories. You simply can't make a bald statement like "This is how much an hour's bike ride burns." But you can, if you're persistent, get a good idea of how much YOU burn, on average, over time, per hour, at a given weight.
Too many variablesmleptuck
Jan 14, 2003 9:27 AM
Thanks. I realized that was certainly one way to calculate it, but was hoping there was an easier method.

Guess I'll just ride until I get down to my target weight!
AdviceOldEdScott
Jan 14, 2003 9:41 AM
Best and easiest way I know of to lose weight:

Multiply the weight you want to be by 15. If you want to be 200 pounds, that's 3000.

Eat that many calories a day. Whatever you want to eat. 3000 calories is lots of food. (If you weigh 240 right now, you're averaging 3600 calories per day).

Ride your bike.

Don't give it another thought. In a few short months you will weigh 200, and you will never have felt deprived.

Eat like a 200-pounder, and you will eventually BE a 200-pounder.