Why does my heart rate vary drastically day-to-day during cardio?

April 19, 2006 9:10 AM

Why does my heart rate vary drastically day-to-day during cardio? 120 one day then 160 the next under same conditions.

I go to the gym around 3 days a week and always use the elliptical machine for 25-40 minutes. It has one of the usual hand heart rate monitors. I typically use the same resistance/incline/strides-per-min, but some days my heart rate is much higher. For example, it is usually around 110-120/min, however, today it was 150-160/min. I'm not really complaining, on days like this it is a lot easier to break a sweat, but why does heart rate vary so much day to day?

I can think of a few reasons like diet (but what?) or drugs (nothing illegal, caffeine or ephedrine, but I'm not sure those would make it so drastic).

Just for the record, I'm a 25 year old male.

posted by wolfkult to health & fitness (12 answers total)

You might be dehydrated... it makes a huge difference.
posted by mert at 9:12 AM on April 19, 2006

i second the hydration.

also i find on days where i didnt hit my calorie intake i tire so much quicker while working out.

i dont monitor my heart rate so cant comment directly. but on a day when ive been eating well i can do 30 minutes of HEAVY CV. on a day where i know ive eaten poorly and not hydrated enough after 10-15 mins im shot!
posted by moochoo at 9:15 AM on April 19, 2006

Are you using the same machine each time? My understanding is that the hand heart rate monitors are NOT the best testers of your actual heart rate, but of course I have no research to back that up with. If you want to keep a better eye on your heart rate to determine if it's actually fluctuating that much, you'll probably need to get one of the chest monitors.
posted by bibbit at 9:23 AM on April 19, 2006

What bibbit said. My old trainer (who worked for my gym) told me not to rely on what the monitors on the machines say - they're not always accurate, and if you switch machines at all, you can be pretty sure they'll give you a different reading. If you want a reading that you KNOW is accurate, you'll have to get a separate monitor.
posted by AlisonM at 9:39 AM on April 19, 2006

It's true that the monitors in the machines aren't the best, but they aren't so bad that they would display such a wild fluctuation from day to day.

But do get one of the chest straps. Some cardio machines can actually communicate with them, so you can get a real-time display without wearing the clunky watch.
posted by o2b at 9:39 AM on April 19, 2006

Lack of sleep, blood sugar, over-exertion, how warmed up you are, etc.
posted by callmejay at 9:42 AM on April 19, 2006

Also, heat. The temperature in the building can raise your heart rate.
posted by generic230 at 9:57 AM on April 19, 2006

caffeine?
posted by tiamat at 10:48 AM on April 19, 2006

The more I think about it I think I did almost everything named that could increase my heart rate, today.

I drank two beers last night and went to bed feeling parched, I got a glass of water but ended up drinking only a couple sips. This morning I took a Sudafed (ephedrine) with my diet mountain dew (caffeine). I didn't have anything to eat so I ate 2 or 3 girl scout cookies before going to class and the gym. At the gym, it was warmer and I used a different elliptical than normal as well.

I think everything just added together to form the perfect (heart rate) storm.

Is this a bad thing though? My understanding is that the higher my heart rate, the better the workout I'm getting for the same effort (as defined by time, incline, resistance, strides/min). Maybe I should start a workout revolution where you always go to the gym dehydrated and get corporate sponsorship from the Girl Scouts too.
posted by wolfkult at 11:43 AM on April 19, 2006

I am reassonably sure that a 40-50 spread in pulse is due to either a change in the intensity of the workout and/or faulty readings. I can not imagine the other factors contributing to more than a 10-20 point difference unless you were really dehydrated or having some induced/temporary tachycardia. A higher pulse is not always desireable--what one wants is a steady pulse at the appropriate aerobic level (easily looked up on line). Actually, one of the very best indicators of cardio fitness is the one minute and two minute recovery time from maximal exertion. If you really want to know how your conditioning is going and improving over time check your recovery time. Ways of doing this can be easily looked up and involve nothing more than a watch on which you can monitor seconds.
posted by rmhsinc at 12:24 PM on April 19, 2006

Sounds to me like you were picking up somebody else's monitor, possibly.
posted by konolia at 1:37 PM on April 19, 2006

Are you using Precor elliptical machines? I work out on those every day during the week and the HRTs in those puppies totally blow. I also get a wild variation from machine to machine, sometimes in the same work out session - and sometimes they give me totally wacky numbers, like saying my heart rate is 50 or 60 when it's clearly around 155.

Get thee a heart rate monitor. I need to change the batteries in mine (hence the noticing of the wacky numbers on the Precor machines lately) but it is so helpful, and much more accurate. I got mine at Radio Shack for around $30, and it has served me very well. It broadcasts to the machine for you, so you don't even need to wear the watch.
posted by pazazygeek at 3:53 PM on April 24, 2006