Heat Increasing Heart Rate

Hi All

When I train at home I can sit at 155-160 watts and keep my heart rate in the 130s.
However, when I train at my local gym, (with no aircon), I can only managed around 145 watts whilst keeping my heart rate in the 130s.

I’m assuming generated heat is creating the majority of this difference as I run hot and sweat absolute buckets when I am training there.

So my question is this:
If I want to stay in my aerobic zone (which for me is below 145bpm and 155-160 watts (which I can do at home), when I train at the gym, is it better to maintain the same watts and ignore my heart rate that will shift to over 150bpm or is it better to focus on heart rate which means dropping my power by 5-15 watts?

In case anyone is going to suggest some logical fixes, I can’t move the gym bike and there is no way of putting a fan up or getting more air flow to the bikes. They are fixed where they are. Oh and I’m not intending to change gyms either.
I just want to know which is the more important area to focus on…power or heart rate.

Thanks in advance for all your help :slight_smile:

For work at the intensity you’re describing (sounds like you’re aiming for Z2 in a 6-zone model), I’d stick to the power. Over time your body will adapt to the heat and your heart rate will normalize for the power. If you’re doing stuff in a much higher intensity, the choice depends on the zone and your goals. In high heat situations, I find cooling critical for hitting the target power for sweetspot and threshold, but for things like VO2 Max where your breathing rate is most important, using HR can be a more useful tool.

FWIW, I have a similar scenario here in So Cal because it can get really hot in the summer months. My trainer’s in the garage and on hot days my heart rate is really affected. Sometimes 10 beats higher than “normal”. I choose to bring down the workout intensity as needed (i.e. lower overall power requirements) so the training effect on my body and over system achieves what TR is suggesting for that day. There were times when I didn’t lower the intensity and just go for it. But I’d often be far outside of the prescribed training zone for that workout which stressed the wrong systems and completely changed the training stress.

My thought will be to stick to your power target which will force your body to adapt to the heat, so in the longer term in cooler environments you’ll be much stronger :muscle:

Better to train to power rather than heart rate. However, to redlude97’s point, your power meter at the Gym may be off. If you have power meter pedals you may be able to convince the gym to let you test that theory. Otherwise, you may need to try to get by on power until it cools off and then try to compare the two when temperature isn’t an issue.

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Drop the intensity to match the at home heart rate. Training at tempo and below I’d be using heart rate, FTP and above, power.

Definitely make sure you’re using the same power source for comparison- if not, I’d either do an FTP test on the gym bike if it’s something you use frequently, or go by HR/RPE because your existing zones aren’t necessarily accurate to those conditions.

Regarding the heat- I’ve always been of the mindset that any metric without context is pretty limited, so I’d probably be using some combination of the three and my own judgement. Part of that is considering what you’re actually trying to achieve. If it’s a session where you’re looking to get the most out of yourself power-wise I’d consider that to be the priority unless you’re specifically training for hot conditions, but when it comes to endurance you’ve got a lot more wiggle room and I’d be more inclined to make adjustments in order to keep the effort level appropriate and not impact my harder sessions.

Last time I rode a stationary bike in a gym, all I had was a tiny fan that was smaller than my hand. It felt as if a hamster was coughing on me, gently.

In my mind, you should train by power, not heart rate, but choose your workouts wisely. Either go for less intense workouts (Z1–Z2) for longer. Or if you want to do something like sweet spot or VO2max, I wouldn’t exceed 45 minutes.

One thing, though: most gym bikes aren’t known for their accuracy. I’d use the gym bike’s power numbers combined with a dollop of common sense: you need to remember how hard certain efforts feel on your proper bike with proper power meter and then try to gauge the power readings on the gym bike. I assume you are using TR’s outdoor workouts anyway, and these tend to be more forgiving when it comes to power numbers.

If your goal is to train polarized, on your easy days go by heart rate. If you are using different power meters, on your easy days go by heart rate. In essence, go by heart rate for your easy days.

At gym I use one of two Watt Bikes. They match almost identically when I look at what I can do on each bike and also what my heart rate is at any given power output.
At home I use a Saris H3 which I hold slightly different power outputs at the same heart rate.
However, when I am only doing 140-160 watts, I assume the bikes can’t be that far apart as the output is relatively low

In the normal course of events, the heart beats faster to deliver more oxygen to the muscles.

As body temperature increases, the heart starts working as a heat pump, rather than just an oxygen pump, beating faster to circulate blood to the extremities and surface of the skin where heat can more easily escape.

However, watts is a better indicator of the underlying oxygen consumption. Which is the objective of an aerobic workout.

Although I agree with the other posters about the difficulty in comparing power sources.