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  1. #1
    Twincities MN kuan's Avatar
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    Rainy Day Thoughts on Fat Burning and HR

    Compare two individuals. Both have a MHR of 190. #1 is an athlete and has a RHR of 40, the #2 has a RHR of 60. OK. They both want to lose a few pounds.

    Example 1: Using Karvonen, 50% for #1 is 115. For #2 50% is 125.

    Does #1 burn a higher percentage of fat because he's at a lower HR?

    Example 2: If both workout at the same HR of 125, that's 57% for #1 vs. 50% for #2.

    Does #2 burn a higher percentage of fat because he's at a lower HR percentage?

    I've read in a lot of places that fitter people burn a higher percentage of fat at a higher HR percentage but never figured out why. Is it then just a matter of looking at the numbers, the only adaptation responsible being a more efficient cardiovascular system?

    My suspicion is #1 is correct and #2 is wrong. Thoughts anyone?

  2. #2
    Isaias NoRacer's Avatar
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    What is not disclosed in either example is the lactate threshold of each individual. Since carbohydrate usage increases to around 85-90% once one goes anaerobic, if person #1's threshold is near 50% of MHR (geez, this guy's out of shape for an endurance athlete! Maybe, he's a sprinter.) then he'll be burning less fat and more carbs even though his heart rate is lower.

    Low Resting Heart Rate (RHR) is only an indication of fitness, if over time the stroke volume of the heart increased as an adaptation to exercise, otherwise, it may be simply influenced by drugs (i.e., blood pressure medicine) or just be low sans exercise adaptation naturally.
    2009 mileage = 14,738 miles; 2010 mileage = 15,234 miles; 2011 mileage = 17,344 miles; 2012 mileage = 11,414 miles; 2013 = 12,169

  3. #3
    Oil it! sfrider's Avatar
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    Quote Originally Posted by kuan
    I've read in a lot of places that fitter people burn a higher percentage of fat at a higher HR percentage but never figured out why.
    The more fit you are, the greater the stores of intramuscular fat. The problem with analyzing VCO2/VO2 ratios is it doesn't tell whether it's intramuscular or subcutaneous fat that's being burned.

  4. #4
    Twincities MN kuan's Avatar
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    Quote Originally Posted by NoRacer
    What is not disclosed in either example is the lactate threshold of each individual. Since carbohydrate usage increases to around 85-90% once one goes anaerobic, if person #1's threshold is near 50% of MHR (geez, this guy's out of shape for an endurance athlete! Maybe, he's a sprinter.) then he'll be burning less fat and more carbs even though his heart rate is lower.

    Low Resting Heart Rate (RHR) is only an indication of fitness, if over time the stroke volume of the heart increased as an adaptation to exercise, otherwise, it may be simply influenced by drugs (i.e., blood pressure medicine) or just be low sans exercise adaptation naturally.
    That kinda falls in place too. Can we assume that a person with a RHR of 40 should have a higher LT than a person with a RHR of 60? At least in most cases?

    Intramuscular fat? Does the body discriminate about what type of fat to burn?

  5. #5
    Senior Member DannoXYZ's Avatar
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    yeah, I think it's more related to LT than HR. It's the muscular-force that determines fat vs. carb. utilization and once you're exerting so much force that you're over LT, very little fat is burned. So it would appear that using lower-gears and spinning would utilize more fat because it requires less muscle-force for the same speed. Which raises HR too.

    As for LT vs. RHR.... I'm not sure if there's a correlation since LT can occur over a variable range depending upon gearing. Pushing bigger gears would have LT occur at say... 150bpm while spinning smaller gears would have LT be around 170bpm. As you get more fit, RHR drops while LT increases..

    "I've read in a lot of places that fitter people burn a higher percentage of fat at a higher HR percentage but never figured out why. Is it then just a matter of looking at the numbers, the only adaptation responsible being a more efficient cardiovascular system?"

    It's partly muscle-efficiency, that is, aerobic-power generated for any given amount of oxygen consumed. With training, LT and VO2-max does increase, but not as much as muscle-efficiency. You may see a 10-20% increase in LT & VO2-max, but power-generated at LT can increase by 100-200%. Let's take some examples, if subject #1 & #2 start out with the same fitness, same MHR and LT levels. They can both generate about 200watts @ LT around 170bpm. But #2 does more training and increases his muscle-efficiency more to 400watts @ LT and same 170bpm. These two guys go for a ride later at the same 200watts output. Subject #1 is riding at 90% of his LT at that output, while #2 is riding at only 50%. Subject #2 will be burning more fat because his muscles are operating at a much lower percentage of their max and will be utilitizing a higher percentage of low-twitch aerobic muscles.

    One of the most efficient athletes I ever saw at the OTC the summer I was there was a football player. He generated the most power per oxygen consumed they've ever tested... unfortunately his mass and bulk would limit his potential as a cyclist.

    "Intramuscular fat? Does the body discriminate about what type of fat to burn?"

    I haven't found anything on discriminating between intramuscular fat vs. adipose tissue. I would suspect that your body redistributes this anyway. What I read is that higher triglyceride-levels in the blood does increase fat-burning. This can be triggered by various glycogen-sparing techniques like coffee that stimulates glucagon production and triggers the fat-cells to dump their supply into the bloodstream to be used for fuel helping stretch out the glycogen supply and fending off the bonk for longer.
    Last edited by DannoXYZ; 09-03-06 at 02:21 PM.

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