It’s something I’ve noticed on several of my longer rides, particularly if they are in the morning.
It’s like it takes quite a while for my heartrate to settle down.
Today, I rode 127km road at 307w/320w NP, at 33kph. I’m 102kg, 203cm, FTP around 420-435w. Usually, the top of my zone 2 is between 310-320w.
I set out today (after a suboptimal night’s sleep) and it took over an hour for my HR to settle below my Z2 threshold (145bpm). It was then quite happy there for a long time, and I was able to up my power whilst staying under 145bpm. I got a bit of HR drift after I had a pop at a segment, but still, producing more power at the end of the ride than at the start for the same HR.
A point aside - nearly 4hrs at the very top of Z2 is unpleasant!
Just wondering if anyone had any insight, and thanks in advance:
Any other information? What time was this ride? How long had you been awake? Did you eat before you started? If so, was it right before, or hours before? Did you have a cup of coffee? Or six? If this sort of thing a pattern, or just for this ride? There are likely a lot of factors that could contribute to this (you already mentioned suboptimal sleep), so I’m guessing it would take some work to figure out what’s going on.
Same always happens to me if I ride in the morning. Especially a long ride, my heart rate could drop 10bpm from start to mid ride. And often end up with no or even negative decoupling for the long ride.
My morning power is a lot lower than my afternoon power at the same heart rate so I guess that’s the reason.
Heart rate gets lower as I properly wake up and digest breakfast.
I hadn’t been awake long enough really - I am on late shifts this week, so I’d been awake 3hrs when I set off and had had two breakfasts, totalling about 1700kcal. Three cups of coffee.
It’s almost always the case that I can put out more power for the same heartrate in the afternoon. I commute to work on my bike sometimes too, and my commutes in the afternoon for the late shift are always stronger than for the early shift.
It’s a strange one, isn’t it! It’s apparent enough now that I wouldn’t often bother trying for a segment pb early in the morning as I know I’d be 5% stronger in the afternoon.
If you are talking about negative decoupling I experience the same thing. I’m usually between -3% and -5% during longer z2 workouts, but have seen as low as -8% at times. I’ve done some googling without finding any clear explanation.
My guess is that the metabolism is more efficient in the second half of the workout. If anyone has a better theory you are welcome to chime in.
If it were me, I’d start here. Try heading out after a much smaller meal and without all the caffeine and see how your HR tracks. It doesn’t have to be a 4hr ride if you’re concerned about fuelling beforehand, just long enough to see the effect on HR for the first 60-90mins.
What time of the day were you doing these rides? If you were feeling too-cold at the start but then warmed up & felt comfortable… I wonder if that would explain HR drift.
Also, check your cadence profile over the whole ride. If your self-selected cadence drops over the course of a ride, then it will encourage a slight drop in heart rate.
Lower cadences cause:
Lower muscle pump
Increased pedalling force for the same power output, ensuring greater recruitment of type-2 fibres → less oxygen is required for the same power output, therefore less cardiac activity is required.
It is a common occurrence for me too. During the weekends I always ride in the morning, two hours after a good breakfast with a cup of coffee. It usually takes almost an hour of riding for my HR to return to the normal level.
I do most of my weekly intensity on Fri, Sat, Sun, so usually take Monday off. On my Tuesday z2 ride (it also happens on an easy spin on Monday, if I decide I need that for recovery), my HR will drop after 30-45 minutes. I always just assumed I was burning off some unused lactate or just getting muscles loosened back up.
My HR is usually higher when I ride outside, and I finally decided that is because I almost always eat a full breakfast before outside rides, but rarely before indoor rides (mostly do my z2 inside).
Are you a “morning person” or an “evening person”?
I have the same thing - I generally perform much better on workouts in the afternoon/evening. I think it’s pretty normal that some people are better in the morning and some are better in the evening. With my running, my HR for the same pace is always much higher in the morning compared to the evening. I am pretty sure this is a well known phenomenon and e.g., Olympic athletes train specifically at the time of day when their events are going to be held.
I get pretty steep negative decoupling on morning workouts, especially if I had a couple of beers the night before. I don’t really think much of it any more. I had -2.8% in this TrainerRoad 90 minute sweetspot workout on the 16th for example:
It’s a tricky one for me, as I’m very large and my calorie usage is somewhat extreme. For example. I had 8000kcal yesterday in total, and burned close to 5000kcal on the bike. So 1700kcal for breakfast isn’t so much, in the context of what I usually eat.
I’m more of a morning person, but I started a job in December that has me working alternating morning and evening shifts (one week of each). I absolutely hate the disruption to my circadian rhythm. But even predating that, I was always stronger in the afternoon.
It’s interesting to see how common this issue is. I had no idea.
This ride was started at 11:00. I wasn’t cold as it’s quite mild here at the moment, and I don’t really feel the cold anywway.
Good tip on the cadence profile - I’ll check that. It has been noted by my training partner that the higher my power output, the higher my cadence. That is to say, I seem to put out a similar amount of power on each pedal stroke so typically go faster only when I pedal faster. My cadence on this ride was just over 80rpm
Watch what your heart rate does after a meal. Mine always goes up 5-15 bpm depending on how large of a meal I eat, and that’s just sitting. It will certainly cause an increase in the bike if you eat anything substantial within an hour or so. This even goes for a coffee stop where you eat a couple of big pastries.
Vasodilation of blood vessels, etc and “turning on” your bodies cardiovascular system to handle the work is the other part of it. It takes me usually 20 minutes before I start to notice a decrease in HR, sometimes up to an hour before the heart rate is fully settled in. This is one reason I’m not a fan of these 10-15 min “warm ups” before slamming threshold or vo2 work. You can almost guarantee your body isn’t fully ready if it is a morning session, and likely that even in the afternoon as well. I would also recommend starting at zone 1 for at least 20-30 mins before going to the top of zone 2 to at least give your body a chance to warm up. I have also read that the first 30 mins or so of riding is generally more glycolytic, so by reducing the power output during the warmup you retain more glycogen for later on in the ride.
That’s a really insightful and useful answer - thank you. I will take onboard the warmup protocol and take note of my heart rate after meals. I eat almost constantly, so hard to find a time when I’m not digesting something.
