Howdy all, I've been doing stationary bike twice a week in the gym and I've noticed something odd. I use a consistent cadence and resistance level every workout, but sometimes even pushing hard, my HR never goes out of zone2, where as normally I spend most of my time in zone3 and zone4. My pre-workout habits, sleep, restfulness, are all the same each workout as I keep to a regular schedule.

My question is does this happen to you and have you found any correlation that might explain why? I'm wondering if dehydration might play a part. I've also had my heart checked out by a cardiologist in the last few years and I'm not worried about any health issues. It's just a strange thing I'm trying to figure out.

The images below are 2 sessions. My METS, avg watts, cadence, were all nearly identical.

HR is funny that way. Depends on other stuff. But if you have any doubts or even just question about whether your heart is in shape for you to get in shape, then you should talk to a heart doctor or other healthcare professional.

If you really were pushing as hard as you could and your HR didn't go up, then that might be a health issue. How did you set your HR zones?

Being a little dehydrated can cause your HR to beat faster than is normal. And of course caffeine and other drugs factor in too.

I had my heart checked out a few years ago and it's fine. I'm not worried about any health stuff, just strange that sometimes I struggle to get my heart rate up even when pushing.

The 2 Images show way different 'efforts' !
The 2nd effort has a big/longer segment of Zone 3, and THAT is what has your HR at a higher level.
Hence the higher avg HR !
Both are good to do.
Do the stronger, large section of Z3 effort when you feel the body is capable.
Switch to the easier Z2 on those days when you might feel you're in a weaker condition, at the time of the workput.

The Z2 workout is important in helping the body adapt to the overall riding process, and does have solid conditioning results.
BUT do Z2 for a longer time period - in what you show, try for 20 + minutes... It's an endurance building zone,
Roughly equal days alternating between Z2 and Z3 workouts is a good way to start. As yo become stronger you can lean just a bit to either one, depending on how the body feels....
None of what I say is actually a 'training' program - it is purely an overall 'conditioning' thing...
I know you've been focusing on weight lose, along with overall conditioning... so this would be a good 'regular' thing to do...
Of course the 'nutrition' side (quality and quantity balancing) is a key part of all this...
Zone 3 efforts are usually safe for most, but it really depends on what you and your MD say you're capable of.
A steady diet of Z2 & 3 workouts is a very good thing ! ( and yes, the 20 BPM increase is expect for the higher effort workouts).
Keep it up !
Ride On
Yuri

Those are only 10 minute workouts. Is your machine set at a calibrated resistance and your cadence is also measured and held constant from beginning to end?

As already said, HR depends on lots of factors. It's affected by heat, by your hydration state, but your accumulated fatigue, by your fitness.

Personally, and anecdotally, I seem to have two different HR regimes. When I'm not at my best fitness, my HR is higher for a given effort - of course. But also, this is when I can experience my maximum HR. When I am more fit, my body seems to switch into a low HR mode- I can complete a very similar ride at lower HR, but also, it's harder for me to reach my maximum HR.

Unless you have some other reason to suspect something is going on, don't over-think this one.

The variability of HR is one of the reasons that many people base their training on power, rather than HR.

Still, how did you set your HR zones? It sounded as if you said you couldn't get your HR up any higher on several occasions. That might indicate you have a health issue. Or... you didn't set your HR zones correctly and you are hitting what is your actual HRmax.

The machine/device won't display the correct HR zones if you don't set them up with the correct information.

I use a set resistance and cadence on the bike and it measures avg watts, peak watts, avg mets, peak mets, and they were comparable between the two runs. When I start I go hard the first 90 seconds, 80rpm to get my HR up, then I avg 60-65rpm. I did that in both. The "effort" recorded by the apple watch is a measure of HR, not a measure of my actual effort, the avg watts, etc the bike tells me is a better measure of that.

I was trying to get my HR up but my legs were giving out before my heart was. My breathing effort was similar in both runs, in fact the 142bpm run I felt like my breath was relatively easy.

My HR zones are apple watch, the machine only tells me my HR, (which matches the apple watch).

If you're curious it's a planet fitness stationary bike, manual mode, 16 resistance

It's frustrating when you are pushing hard and your HR just doesn't want to go up.

I do exactly the same cardio exercise three times a week. Exactly the same, almost to the second. (I'm somewhat red-faced to admit that it is a Gilad video from 1992, doing step aerobics). I noticed that on some occasions, my heart rate would be ~30 bpm lower at maximum, and there would be almost no time in Zone 5. The cause? Metoprolol. If you're on beta-blockers and don't take them at the same time every day, there will be a change in your workout heart rate. There are some natural things that have similar effects to beta-blockers, but they do not affect adrenaline. I don't know if any foods or supplements would affect your workout heart rate.

This is what I saw when I experimented with varying the time from the last dose (metoprolol's half-life is, meh, about 6-8 hours for me). The "with metoprolol" dose was taken at 7 am. The "without metoprolol" was a skipped dose, and varied the prior evening's dose time. I was shooting for a 10-hour and 20-hour interval, but I often can't quite get my great big giant fat ass into gear.