Exercise, heart rate, & calories burned

September 29, 2007 2:31 PM

Questions about exercise, heart rate, and estimating calories burned.

Forgive the length, but I'm trying to be as detailed as possible.
Background:
I've lost over 100 lbs in the past couple of years by counting calories and exercising. I stopped doing both of those things for a few months after hitting a plateau and then going through a particularly stressful period, leading me to gain back a few pounds. I've been back on track for the last month and seem to be dropping a couple of pounds a week.
Current Routine:
I eat about 1,200 calories a day, which has been my calorie goal since I started losing weight. I eat small meals throughout the day and am not hungry -- I think I could limit myself to 1,000 calories a day fairly easily, but I'm not sure if that's wise. I do 45 minutes of cardio a day on the elliptical and lift weights 3 times a week. Every other day, I do intervals to go between 60% and 85% of my estimated max heart rate based on calculators that factor in age and resting heart rate. I try to keep my heart rate in the 80-85% range on non-interval days. I have a heart rate monitor that uses my age, gender, height, weight and resting heart rate to estimate the number of calories burned. I know it's just an estimate.
Question:
I find that I'm much more likely to work out if I do so in the mornings, as soon as I get up. There's a gym in my condo, so I probably am on the machine within 15 minutes of getting out of bed. I'm not hungry then, and usually don't eat breakfast until around 2 hours after my workout. I fill a bottle of water before I work out, but usually don't drink any until a few minutes into my workout. My heart rate in the morning goes up much faster working at a much lower intensity than it does when I work out in the evenings. When I do work out in the evenings, I have to increase the resistance and really push myself to keep my heart rate above 80% of my max. In the mornings, I wonder if it's getting too high -- it seems like I have to hold myself back to keep it around 85%. Either way, my average heart rate is almost the same, so am I burning the same number of calories? How long before my workout would I have to eat or drink to see it make any difference?

posted by anonymous to health & fitness (6 comments total)

Your blood viscosity changes more than you might expect, depending on how hydrated you are. Try slugging back an extra glass or two of water 15 minutes before the morning workout and see if that changes things.
posted by IvyMike at 3:17 PM on September 29, 2007

For what it's worth, my heart rate when I run is at 96% of the "220 minus your age" rule for heart rate. I don't know rules like that are something you should rely on in any rigorous manner.
posted by knave at 3:35 PM on September 29, 2007

i would imagine that you are probably burning about the same amount of calories. your heart rate might be higher in the mornings because your blood sugar is low (even if you don't feel hungry, you haven't eaten in at least 8 or 10 hours). try drinking some juice before.

fwiw, 1,200 calories seems awfully low if you do 45 minutes of cardio a day, unless you are only 4 feet tall or something. have you spoken to a nutritionist? if you are plateauing, it may be because your body thinks it's starving (and no, you don't always feel hungry when this happens) or you've pretty much reached your "ideal" weight.
posted by thinkingwoman at 4:01 PM on September 29, 2007

Seconding the hydration suggestion. Dehydration really does affect heart rate.
posted by konolia at 4:51 PM on September 29, 2007

Either way, my average heart rate is almost the same, so am I burning the same number of calories?

I'm not sure about the rest of your question, but I can tell you that studies have shown that people who exercise in the morning continue to burn extra calories throughout the rest of the day. You'll burn the same amount of calories *during* the same exercise morning or night, but if you exercise in the AM you'll jump start your metabolism for the rest of the day.

There are also several other reasons to exercise in the morning.

Either way, my average heart rate is almost the same, so am I burning the same number of calories?

Also, I would think that your resting heart rate would be at it's slowest right after waking up. Would that account for the seemingly easy "increase" once you start working out?
posted by Brittanie at 6:15 PM on September 29, 2007

I'm not sure about the calorie burn, but I think if you're doing interval training you shouldn't worry about your heart rate during the "work" periods. Just go as hard as you possibly can. This is assuming the interval training is something like fifteen or twenty minutes, 90 seconds on, 90 seconds off, or even shorter intervals.

Also--you say you don't eat until two hours after your workout. This is a really bad idea and will actually hurt your weight loss. There are numerous sports studies indicating that you need to get protein in you as soon as possible after your workout--within a half hour--or your body will start cannibalizing your muscles rather than your fat and the effectiveness of the workout will be greatly reduced.
posted by schroedinger at 6:45 PM on September 29, 2007