Heart rate low in the morning, high in the afternoon - whats wrong?


me: beginner (first year cycling), 60kg+ overweight, male, 37 years, 180max heartrate, live in totally flat lands

I honestly do not understand how heartrate works and how it does correlate to power.

My awkward observation: When I drive to work in the morning below LTP (which is 141w for me), my heartrate is between 115 and 120, easy, light, maybe not really sport at all.

But when I sit on my bike in the afternoon, back home, my heartrate is immediately at 125 even after 10 sec cycling and after 1min - power again below LTP - it stabilizes between 135 and 140. And I feel it, too, breathing gets heavier, feels like serious sport.

That is consistent, every day. So same way, same power (no wind and no climbings at all, flat land), but the morning ride feels like nothing and afternoon ride feels like serious effort.

How could that be explained, what could be wrong? And if its relevant, my work: Sitting infront of a computer, no moving at all.

Caffeine intake at work?

Zero. But a lot of carbs in form of bread, bun, sugar.

How’s your hydration during the day? Most people don’t drink enough. Will increase your hr a few points for sure


How flat is flat? 1-2% false flat grade on way home will do that.

Wind. There is always some resistance, never truly still. Could be slight headwind on way back?

Hydration may be suboptimal. But +10 to +15 heart rate? Its not only the heart rate, it really feels much harder.

It is really flat, like flat-flat, 0,1% or less. We are talking 3-7m height on a 10 km course.

Yes, wind is here, but like I said: Power is matched. So tecnically wind should play no role (as even climbs should not).

You would be surprised at how much hydration plays a role in HR - if all things are truly equal, try measuring and managing your hydration through the day and see if it makes a difference.

Also, regarding wind, you say power is matched but that could be the result of slightly harder work to achieve that power due to the resistance you face on way home. Power will be same, but HR and effort will be higher/harder to achieve same power output.

You could be sensitive to some element of your diet (salt, sugar perhaps) at work. Or maybe work stress? Or you’re REALLY a “morning person”!

Is it maybe much warmer outside when you ride home?

Stress factors at work?
Do you measure HR while at work to see how it changes?

you might find it interesting to plot your heart rate over the day. I am looking at my heart rate over a day where I did a 4 gravel ride. Before the ride my heart rate was quite low, of course it rose during the ride, but what is interesting it declined some but plateaued well above where it was before the ride. So stressors will elevate your heart rate and the base line then shifts so during the day it is likely your heart rate shifts and so the baseline is raised when you ride home, thus all of the effects you report. So if there are stressors during the day then it may be a part of the answer? in all things being equal something is shifting the whole graph upwards for you later in the day. Have you looked at your heart rate before you start your ride in the morning and in the time after work before you start your ride home. I bet the starting points are different.

Yes, after checking: starting points are different, heart rate ist raised before riding the bike, even above 100 bpm, minutes before leaving work. Still, reason unclear. Not many stressors at work.

Some variability through the day is normal but what you describe seems unusual, but I’m not a doctor. If you are concerned about your heart, perhaps actually see a doctor. Especially given you’re starting a potentially intense exercise program from a fairly sedentary lifestyle. Better safe than sorry

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