Discrapancy between HRM calories, and Power Meter (Joules)

oeagleo
oeagleo Posts: 70 Member
in Fitness and Exercise
Okay, I'm normally not too concerned with how many calories I burn during exercise, however, I am curious about a huge discrepancy between the calories burned during my cardio classes, (Silver Sneakers), my weight training, and bike riding. The normal calorie burn is fairly constant for the Silver Sneakers classes, as it is with the weight training, averaging about 350 per hour. However, when I use a power meter for a ride on my bike, it shows that for a 20 mile, 2 hour ride, I've burned 447 kJoules, or 428 kCalories. The HRM (A Suunto Ambit 2) shows that using the heartbeat values, I've burned 1480 calories! That is a HUGE difference.
So, my question is, which is a more accurate reflection of actual calories burned, and yes, I know the realtionship between heat, calories, joules, etc, the question is that the bike ride was way more exertion, and for a longer time than a single hour of Silver sneakers. Breaking down the bike ride into an hour, it would be about 740 calories, which seems about right using "perceived exertion" but only 214 for an hour using the "heat/Joules" formula seems awfully light.

Need input

Replies

  • brianpperkins
    brianpperkins Posts: 6,124 Member
    what model power meter are you using?
  • oeagleo
    oeagleo Posts: 70 Member
    I have an iBike Newton+, and really like it. I understand the science behind it, and it's way less expensive than any of the direct force power meters.
  • brianpperkins
    brianpperkins Posts: 6,124 Member
    I have an iBike Newton+, and really like it. I understand the science behind it, and it's way less expensive than any of the direct force power meters.

    Without seeing the data from the Newton, it's hard to tell. Did the Newton see your heart rate along with the Suunto or did the strap only report to one device? There are so many variables that could result in either device not providing an accurate reading that it's impossible figure out from what you've provided. It could be something as simple as the wrong mass data or wind sensor obstruction on the Newton.
  • oeagleo
    oeagleo Posts: 70 Member
    The Newton connects to the HRM strap, along with the GSC-10 on the bike. It also connects to the Suunto, a great thing about the Ambit 2, no longer are the Suunto devices limited to their own connection protocol, the Ambit 2 uses ANT, just like the Garmin, etc. I was thinking about it, and the Newton simply calculates the amount of force that is required to make the bike go given the current situation. The HRM actually checks the heart rate, and for me, with I ride the bike, the Heart Rate really goes, so to speak. I suppose it's because my VO2Max is not very high, (around 8) due to my inactivity for so long. So, on a bike ride, my heart rate is at a sustained high rate, and given my low VO2Max, I wind up with an average heart rate of 140, which is in the 83% of max range. That would indicate to me a large amount of stress on my body, and, subsequent calorie burn. The Newton, while I really like the metrics it provides doesn't take any of that into account, calculating only the amount of force needed to overcome the opposing force at the time.
    I wish I knew a lot more about the correlation between heart rate, calories, and the calculation of calorie burn using the joules method.

    So, once again, the Newton connects to the Suunto, and the data from the Suunto is imported into SportTracks, which gives me the 1480 calories burned for yesterday's ride. The 428 calorie burn comes directly from Issac, the software that the Newton imports, and analyzes the data with. Generally, the numbers are close, but not exact, something I still don't understand.. Issac reports the max power for that ride at 266 Watts, with an average power of 57.9 watts. SportTracks reports 231.6 Max watts, and an average of 70.4 watts. Yeah, I'm confused.. :-)
  • BrianSharpe
    BrianSharpe Posts: 9,248 Member
    At 10mph you're not going too hard but 217 cal/hr sounds very low, 700 per hour sounds closer to reality (the only Suunto equipment I own is my dive computer, it's a reputable company and I'd put more faith in their HRM than a low end Polar or the like)

    I know it's difficult to compare rides (every one has it's own profile) but my 19km bike commute takes me a little over 45 min (which I think translates into about 15mph) and my Garmin 610 estimates around 600 cal each way.
  • JSHamm
    JSHamm Posts: 12 Member
    Okay, I'm normally not too concerned with how many calories I burn during exercise, however, I am curious about a huge discrepancy between the calories burned during my cardio classes, (Silver Sneakers), my weight training, and bike riding. The normal calorie burn is fairly constant for the Silver Sneakers classes, as it is with the weight training, averaging about 350 per hour. However, when I use a power meter for a ride on my bike, it shows that for a 20 mile, 2 hour ride, I've burned 447 kJoules, or 428 kCalories. The HRM (A Suunto Ambit 2) shows that using the heartbeat values, I've burned 1480 calories! That is a HUGE difference.
    So, my question is, which is a more accurate reflection of actual calories burned, and yes, I know the realtionship between heat, calories, joules, etc, the question is that the bike ride was way more exertion, and for a longer time than a single hour of Silver sneakers. Breaking down the bike ride into an hour, it would be about 740 calories, which seems about right using "perceived exertion" but only 214 for an hour using the "heat/Joules" formula seems awfully light.

    Need input

    So as not to break a commandment, this is a copy paste from another forum post:

    "To work out energy expenditure in joules, you multiply average power (/1000) by time in seconds. Thus, the work done in 1-hr at 190 W avg is 684 kj (0.19 x 3600). To convert this to kcal you divide by 4.18, i.e., 164 kcal.

    However, the human body when cycling is only around 25% efficient (normal range ~ 20 - 26%), thus, this needs to be calculated, to work out the human energy consumption, i.e., 164 / 0.25 = 656 kcal."

    So specifically to your #'s

    70.4 Watts for 2 Hours:
    ((.0704 * 7200) / 4.18) / 0.25 = 485 calories or 242 per hour

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