Question on heart rate and metabolism

bgt84
bgt84 Posts: 7
in Fitness and Exercise
Hi all,

I'm a 6'0", 220lb, 28-year-old male. For a few months I had been following a pretty strict 1,550 calorie/day diet as that was what MFP had recommended and I didn't really know anything about your basal metabolic rate or TDEE or any of that stuff. Since learning about that and discovering that I was probably doing more harm than good eating that few calories, I took about 10 days "off" and basically ate at or near my TDEE (about 3,300 calories), and now I'm jumping back on the diet train and eating a more reasonable number of calories (my BMR is around 2,100, so I'm aiming to eat about 2,300 calories per day before any exercise).

Prior to taking my break, I had noticed that my heart rate when exercising had decreased considerably. My "workout" basically consists of 10 minutes of walking at 4.1mph at a 3% incline, followed by 10 minutes at 3.7mph at a 10% incline, followed by 10 minutes at 4.1mph at a 3% incline. Occasionally I'll repeat this routine twice, but generally just once per day. For a long while my heart rate was 125-130 during the first 10 minutes, 160-165 during the second 10 minutes, and back down to about 130 by the end of the third 10 minutes. Lately, however, my heart rate had gotten down to maybe 105-110 during the first 10 minutes, 135-140 during the second 10 minutes, and back down to about 110 by the end of the third 10 minutes. At the time I was chalking that up to being in better shape, but now I'm wondering if it was maybe because my metabolism had slowed down from eating too few calories. Since I've started exercising again, my heart rate is back where it was originally (130, 165, 130), and I'm sweating a lot more when exercising and feel a little bit more "worked out" afterwards. Is it possible this is due to my metabolism getting more "back to normal"? If so, is my heart rate something that I should keep an eye on in the future to avoid my metabolism slowing down?

Thanks all,

Replies

  • jonnythan
    jonnythan Posts: 10,161 Member
    Your heart rate went down because your cardiovascular system got better at moving oxygen around your body.

    Lance Armstrong's heart rate would barely go above resting doing 4.1 mph on a 3% incline. That doesn't mean his metabolism is lower than yours; it means his heart and blood vessels are much more efficient at delivering oxygen.

    Incidentally, this is why I don't like HRM's for measuring calorie burn. The two are only peripherally related. The only true way to measure calorie burn is by measuring how much oxygen you consume. This isn't practical. I think FitBit/Nike/Jawbone have the most accurate way to do this, by measuring how much your body actually moves.
  • bgt84
    bgt84 Posts: 7
    Alright, that makes sense -- thanks. I guess my question then is, what's the cause of my newly increased heart rate when exercising? Is it just because I haven't been exercising for 10 days and my body isn't used to it? Should I expect my heart rate to go back down once my body is "back to normal"?
  • jonnythan
    jonnythan Posts: 10,161 Member
    Alright, that makes sense -- thanks. I guess my question then is, what's the cause of my newly increased heart rate when exercising? Is it just because I haven't been exercising for 10 days and my body isn't used to it? Should I expect my heart rate to go back down once my body is "back to normal"?

    Tough to say. Could be something as simple as "the treadmill's incline setting was off calibration and has since been fixed" or something. Or the weather or humidity, when you're working out, your weight, your lean mass, whatever.
  • scottb81
    scottb81 Posts: 2,538 Member
    Alright, that makes sense -- thanks. I guess my question then is, what's the cause of my newly increased heart rate when exercising? Is it just because I haven't been exercising for 10 days and my body isn't used to it? Should I expect my heart rate to go back down once my body is "back to normal"?
    In 10 days you will lose a little fitness. If the HR isn't back down within 2 weeks then look for another cause.
  • Mokey41
    Mokey41 Posts: 5,769 Member
    I find if I don't run for a few weeks my HR increases when I get back to it but it usually comes back down within a few runs. The longer you're off the worse it is.

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