Back at the beginning of the month, my Wednesday WHEE diary focused on the calorie burn numbers reported by heart rate monitors and the cardio machines at the gym. Since then, I've gotten a bit more additional data that I would like to share with you.
WHEE (Weight, Health, Eating and Exercise) is a community support diary for Kossacks who are currently or planning to start losing, gaining or maintaining their weight through diet and exercise or fitness. Any supportive comments, suggestions or positive distractions are appreciated. If you are working on your weight or fitness, please -- join us! You can also click the WHEE tag to view all diary posts
Lies, Damned Lies, and Cardio Machines
The gym where I work out (not often enough, alas - thank goodness the weather has been good for bike commuting) includes spinning classes as one of the services available to members. One of the gym's locations here in Austin allows members to use the bikes when classes are not in session. I thought this would be a perfect opportunity to compare the calories reported by my heart rate monitor to the calories reported by my bodybugg. I could have used one of the recumbent or upright bikes on the exercise floor, but the bikes used in the spinning classes allow one to adjust the seat height, the handlebar height, and the forward-back relationship of the saddle to the pedals.
On September 16th, I got on one of the spinning bikes for 1/2 hour from 4:30 to 5:00 PM. I did my best to keep my heart rate as close to 127 bpm for the entire half-hour. I chose this heart rate as being well within (approx. 72%) my aerobic heart rate range, and a reasonable heart rate to maintain for an extended time period. At the end of the interval, my heart rate monitor reported that I averaged 127 bpm, and the calorie count was 292 calories. What did the bodybugg show?
As you can see, the bodybugg showed only 136 calories - less than half what the heart rate monitor reported. Which number is more trustworthy? Of the two, I think the bodybugg is closer to the truth.
However, some bodybugg users on the Apex Fitness forums have compared stationary cycling to steady running on a treadmill, and have found that for the same average heart rate (thus level of cardiovascular exertion), the bodybugg reports significantly smaller numbers for the stationary bike than the treadmill. They've suggested wearing the bodybugg on the upper calf instead of the upper arm to get a more accurate reading.
Just for fun, I strapped my bodybugg on my leg instead of my arm, and did another half-hour back on Sept. 16:
For the second half-hour, my heart rate monitor showed 127 bpm and 290 calories, but the bodybugg showed 326 calories - even more than the heart rate monitor! Sorry, but I don't think so. I think the bodybugg numbers (when the 'bugg is on the arm, that is) are closer to the truth than my heart rate monitor.
The 'bugg may indeed underestimate cycling calorie burn - according to my stats on the Apex Fitness bodybugg site, I seem to have lost more weight than could be accounted for by the calorie burn measured by the bodybugg. But wearing the 'bugg on my calf grossly overestimates calorie burn during cycling, in my opinion.
I stand by what I said back at the beginning of September:
It's easier, and probably just about as accurate, to take the numbers from the cardio machines and divide by two. Just cut 'em in half before you start computing your daily calorie burn. This will help you keep your expectations in line
Since I was already on the spinning bike, I decided to stay for the scheduled 5:45 PM spinning class back on September 16th. My heart rate monitor showed I averaged 152 bpm (that's about 85% of my max heart rate!) and burned 734 calories. Here's the bodybugg data:
I think 301 calories is less than I really burned, but 734 is WAY too much. I suspect the actual number for that hour was more like 450 or 500 calories, given that the "official" range (based on VO2 Max lab measurements) for calorie burn per hour of cycling is 300 to 600 calories.
Exercise "afterburn" - how long does it last?
Here's a couple more pics from September 16's adventures -- when I hover the mouse over the graph on the bodybugg site, it gives the average calories burned per minute for the time interval. As you can see from this screenshot:
Around 1:18 PM I was burning 1.1 calories per minute, and I burned 158 calories between 12:48 PM and 2:48 PM.
Here's what I did in the two hours after my spinning class:
Two things from this:
* Afterburn is real - I burned twice as many calories
after my gut-busting spinning class (85% of max
heart rate) as I did sitting at the computer earlier that afternoon.
* Unfortunately,afterburn doesn't last that long - by the end of
that 2-hour interval after my spinning class, my calorie burn was
back down to 1.1 calories per minute, the same as during my lazy
afternoon.
Last night's WHEE diary stated as fact that afterburn lasts "...for up to 24 hours after a workout." Unfortunately, it ain't necessarily so. If you've just finished a hard weightlifting workout, you might be burning more calories over the next 24 hours. But if you're doing cardio, two hours seems to be about as long as the afterburn lasts.
Upcoming WHEE diaries:
September 30
Weds AM - yr humble servant
Weds PM - ???
October 1
Thurs AM - A DC Wonk
Thurs PM - ???
October 2
Fri AM - ???
Fri PM - ???
October 3
Sat AM - ???
Sat PM - Edward Spurlock (Kessler, Ch. 11)
October 4
Sun AM - louisev - Turtle diary
Sun PM - ???
October 5
Mon AM - NC Dem
Mon PM - ???
October 6
Tues AM - Clio2 (Kessler, Ch. 12)
Tues PM - ???
October 7
Weds AM - ???
Weds PM - Edward Spurlock
I am applying for a new position at work. If I get it, I'll be working M-F most weeks (instead having Tues and Weds off), so I won't be able to post morning diaries any more. I'm grabbing the Wednesday evening diary slot for next week, just in case -- wish me luck!