Higher heart rate in a.m. versus post-lunch workout

[sue320]

I've been trying to change my routine to getting up first thing in the morning and doing my workout. What I'm finding though is that I'm less motivated and have less energy than if I wait until just after lunch (even with having a quicky breakfast). I also notice that I reach and pass my target heart rate zone during my a.m. workout versus my post-lunch workout. Don't misunderstand...I do get within my zone during post-lunch workout, I just tend to exceed it during my a.m. workouts. What gives? I have a foggy recollection of some health information that pertains to this but I just can't quite get a hold of it in my brain (does THAT make any sense?).

TIA
Sue <><

 

[gingerdavis]

Here are my thoughts: your heart rate is higher in the morning because cortisol levels are highest in the morning hours and your blood pressure is lowest in the morning hours.

Since I'm not sure what your background is with endocrinology, here's a little description: Cortisol is a hormone that is released 1) when animals are stressed and 2) in all animals at regular times during the day/night. Cortisol levels are important in heart rate, blood pressure, and other physiological functions. You get a small regular surge in the mornings and this raises HR from what it was while you were sleeping.

I've experienced the higher heart rate in the morning (versus afternoon workouts) and I've been a morning exerciser all of my adult life.

The blood pressure part: because we don't drink while we sleep, most animals are on the dehydrated end of the scale in the mornings. After drinking and absorbing the water and food, blood pressure goes up. This might not help as much after just a breakfast versus a breakfast and a lunch. If blood pressure is higher (post-lunch), the heart doesn't have to pump as fast to deliver as much blood to the tissues. So, if you have lower blood pressure (mornings), you have a higher HR. If you have absorbed more water and food, your blood pressure goes up and your HR can go down because there is more blood to pump around so your heart can beat less frequently. Hope that makes sense. Trying to explain it without a bunch of medical jargon.

Let me know if that makes sense.

The other bit (about it being hard to work out in the morning) is not so clear physiologically to me, but i'll guess it's simply because it is always hard to workout at a different time than you usually do. I know when I try to workout later than mornings, I'm way too tired and have no motivation. If I don't do it in the mornings, even if I have time, it probably won't happen. I've worked out in the afternoons and done a similar workout as usual and been sore the next day simply from the change in schedule.

It is really good to change it up though (unless it makes you workout less). It's almost like changing to a new activity. I would expect it to become easier after a little while as your body adjusts to the new timing.

Ginger

 

[sue320]

Fantastic explanation! Thank you.

Now for a second question...am I still getting the cardio benefits if it takes less effort in the mornings to get my HR up? I figure I know the answer, cardio wise, but another area would be total calories burned.

Thanks again for your answer!
Sue<><

 

[gingerdavis]

Sue,

I'm not sure exactly as far as calories burned. I do know that unless you're on the level of Lance Armstrong as far as fitness goes, it probably shouldn't be of concern.

I read something really insightful one time about this idea: people tend to focus on little details instead of major problems in their diets and workout programs. The idea is that it’s easier to worry about such small things while ignoring the big ones. The big things will usually have more of an impact, but are harder to work on.

For example, if someone (not you--just an example) had a pretty crappy diet but worked really hard on little details of their workout program, it would be a waste of time. Fix the diet and 80% of the work is done.

If, however, you are at a really high level of fitness and have an impeccable eating program, you might benefit from tweaking the small things.

I’d say the benefit of changing your timing of workouts will outweigh any possible downside of more easily reaching your target HR.

So, basically, I don't know for sure about the calories (and it might not matter), but I suspect your cardiovascular system will still benefit just the same (as you suggested).

Now I should heed my own advice and fix the big problems (instead of working on the details) and try to change up my workout timing.

Gin

 

[roe]

Ginger,

Your explanation sparks a question. If heart rate is higher in the morning, why do exercise physiologists tell us to take our resting heart rate first thing in the morning when we wake up for a most accurate reading? This is how the resting heart rate number for the Karvonen formula is determined. Take the pulse for one minute upon waking up (naturally, no alarm clock) for three days, then take the average of the three for the formula. Here is an excerpt from one of my texts:

True resting heart rate should be recorded the morning after a good nights sleep, before rising from bed. Heart rate generally rises throughout the day, and may reach a level as much as 10-15 beats higher than the resting morning value. It is important to note that resting heart rates observed in the morning can be affected by fatigue. Because of this, morning heart rate is a sensitive indicator of signs of overtraining, and can tell us much about the body’s recovery process. Illness, anxiety, drugs, and alcohol can all affect resting heart rate. Short term fluctuations indicate temporary changes in fatigue and recovery, while the long-term gradual decrease indicates positive adaptations in the cardiovascular system.


-Roe

 

[gingerdavis]

Good point, Roe. Maybe it's because in the morning you haven't really been moving around yet? My HR is always lowest in the mornings upon waking (sometimes as low as 40 BPM), but kicks up faster (has a greater gain) during workouts than during late day workouts. That sounds like a combination of hormones to me. A common theme in physiology is that one hormone or event sensitizes the body to another hormone thereby causing a greater gain. So, here, it could be that cortisol causes a greater gain in HR when epinephrine is released during exercise. That's one idea, but I'm not sure if that would make that much of a difference. I see an 8-9% drop in HR when i work out later with about the same amount of exertion. That's a pretty big deal.

I'm thinking BP has more to do with it than cortisol because the cortisol rise is so gentle and because of my own experiences of high HRs while working out in a relatively dehydrated state. Again, BP is lower in the morning due to the body being in a relatively dehydrated state. Once you drink water and absorb osmotically active particles (eating or drinking salty or sugary drinks) into the bloodstream, BP rises and HR can go down a bit.



HR will of course be lower if you're lying down because the pressure the heart needs to create to pump blood to the brain is lower if the brain is level with the heart. So HR can be lower and still supply enough blood to the brain. DO they recommend recumbent positioning for the HR reading? If not, that kind of blows that theory out.

I'd still say that the difference isn't enough to worry about unless we're elite athletes because it won't really make that much of a difference. I am interested for curiousity's sake though.

Those are my thoughts—any ideas/disagreement is welcome. This is all just reasoning in my mind—I have not read any medical journal articles about this effect but the ideas I presented about simply come from what I've learned about HR, BP and the effects of hormones on HR and BP.

++I didn't see the last paragraph before I posted this, but I don't think these ideas contradict the text you quoted. I think I may have overstated the effect of cortisol on HR. HR is certainly lower in the mornings versus the rest of the day. The difference I believe we're experiencing is the gain in HR during exercise, not the baseline rate.

ginger

 

[roe]

Yes, that's the clarification I was looking for - the gain in HR during exercise, not the baseline rate! :7 I was thinking when I read your original post that it might have more to do with BP than HR, although I know when I used to exercise first thing in the morning I had to push myself harder just to wake up, and thus my perceived exertion was definitely higher than a workout later in the day. I never measured it in HR - beats per minute.

Nothing is stated about recumbent positioning for the HR reading. Hmm, interesting question!

-Roe