Coffee and exercise for dummies.

October 3, 2005 6:40 PM

Why is it that even after 7 hours of drinking coffee, my heart rate is about 10-15 beats above my usual heart rate?

I did a brief google and pubmed search on heart rate and caffeine consumption, and this paper from the Journal of Applied Physiology seem to show that there is no remarkable difference in heart rate in the group that had 6 mg/kg of caffeine (which works out to be 360 mg for the average study participant--which is about two cups of coffee, as I understand it). This paper, again from the Journal of Applied Physiology, makes the statement that compounds in coffee depress heart rate. Is there something else in coffee that causes this?

I usually wear my heart rate monitor when I run, but not when I ride my bike. I've found the elevated HR to be the case no matter how long I run and I've run after about 4-5 hours of drinking coffee to the same effect.

I've been running 3 to 6 miles lately if that's a factor.

I'm interested to know why this is the case and if this is just my body being out-of-whack. Next time I run, I'm going to be sure I haven't had any coffee beforehand.

posted by scalespace to health & fitness (14 comments total)

I guess I should also pre-emptively qualify that my HR is 10-15 beats above what my HR would be when running if I didn't drink any coffee.
posted by scalespace at 6:44 PM on October 3, 2005

Why is it that even after 7 hours of drinking coffee, my heart rate is about 10-15 beats above my usual heart rate?

After 7 hours of drinking coffee, my heart rate would be a lot higher than that!
posted by crabintheocean at 6:55 PM on October 3, 2005

Clarification...do you really mean "drinking coffee for 7 hours" or do you mean "7 hours after last drinking coffee"?
posted by Jimbob at 7:09 PM on October 3, 2005

An ICU nurse once told me that caffeine can affect some people for 9 to 12 hours.
posted by mischief at 7:11 PM on October 3, 2005

I think caffeine constricts blood vessels. I think it can give you an endurance boost. More here.
posted by Frank Grimes at 7:19 PM on October 3, 2005

Sorry, I meant that I have a large cup early in the day, say 7 or 8 and I go run later in the afternoon.
posted by scalespace at 7:21 PM on October 3, 2005

I usually grab a small coffee the morning of a road race specifically for the boost. I always perform better at the events, whether it's the anticipation and excitement from all the other people or the caffeine, I don't know. But I've seen studies that show performance is increased. Now you've got me wondering if I should wear a monitor to make sure I'm not going into the "danger zone" (even though I'm only 26, I have an irrational fear of heart failure).
posted by knave at 8:41 PM on October 3, 2005

"Caffeine will continue to have an effect on the body as long as it remains in the blood. The time required for the body to eliminate one-half of the total amount of caffeine consumed (or caffeine's half-life) varies from several hours to several days, but for the average non-smoking adult it is about 3-4 hours, 2. Several factors can lengthen caffeine's half-life, such as some medications, liver diseases, pregnancy, and the level of enzymes in the liver needed for caffeine metabolism. The half-life of caffeine in a pregnant women is 18-20 hours; the half-life in women taking oral contraceptives is up to 13 hours. Other factors, such as smoking can shorten caffeine's half-life. Half-life in a newborn baby may be as long as 30 hours." link

doesn't not even take into effect that since it is a drug effects can vary greatly from person to person.
posted by edgeways at 9:57 PM on October 3, 2005

I've heard the half-life of caffeine as 6 hours, which is to say that a good deal is still in your body thereafter. Drinking coffee any time after morning can reduce their ability to fall asleep for some.
posted by abcde at 11:12 PM on October 3, 2005

Toxicology Filter

Surprising - it takes between 30 and 60 minutes for caffeine to be completely absorbed through the stomach into the blood stream. (This means that instantaneous caffeine kicks are only placebo!) Also, this suggests that the peak effect of your morning cup o joe doesn't happen until an hour or so after you have your first sip (depending on how long it takes you to down the cup and how much you drink).

After caffeine is absorbed completely, the average half life is 3 hours for a healthy adult (which given the running regimen, I can assume you are). In other words, after 7 hours, it likely that you still have around 1/4 of the drug swimming around in your blood stream. For genetic or other reasons, it is even possible that you are slow to metabolize caffeine, exacerbating the effect.

Also, caffeine is metabolized by the liver… so if you drink alcohol, guess what? Your caffeine will stay around a bit longer.

And yes, caffeine is a stimulant; it increases heart rate... so I question your sources.

I wouldn't worry too much, because whatever you are experiencing sounds normal, but then again I'm not a doctor.
posted by |n$eCur3 at 12:33 AM on October 4, 2005

Oh and yes, you found two papers that suggest caffiene depresses heart rate. I can find you at least ten bagillion that suggest the opposite...
posted by |n$eCur3 at 12:54 AM on October 4, 2005

If I have (caffeinated) coffee any later than about 10am, I wake up at around 3:30 the next morning with wide eyes and a fast-beating heart. (Even though I went to bed with a normal heartrate.) That's 17 hours, and my metabolism is usually pretty normal.
posted by Alt F4 at 3:13 AM on October 4, 2005

I have noticed the opposite with beer. My heart rate drops by about 10bpm at full out cardio exertion if I have had a pint in the hour before the gym.
posted by srboisvert at 5:51 AM on October 4, 2005

For future reference, this is all about the physiology and biochemistry of how the cells respond to caffeine.

Madsci.org
posted by scalespace at 12:48 PM on November 22, 2005