I've often wondered the same thing when on my turbo trainer, so will be watching this thread with interest.
It has always struck me as a great way to prepare for a race like Kona, where the temp will be much higher than what I see at home (I live in the UK)

when I workout I just like to sweat. In the winter I will wear enough layers to make sure I do sweat. if your racing in humid conditions (Kona) you need to be acclimated and so have to train in similar conditions. I train mostly in a hot/dry climate and don't do as good when racing in humid conditions.

Depends, if you are going for performance gains (which should be the majority of the time) turn down the heat. If you have a hot race coming up turn up the heat 2-3 weeks before to get your body used to it. I train to get faster, not to see how much I can sweat. Yes hot weather does increase red blood cell count but heat does limit your performance as mentioned.

Not for me it didn't. Furthermore really copious sweating (such as that from a sauna) has implications for mineral loss if done too often.

I generally tend to believe that because the quality of my workouts suffer, I'm getting less training load and therefore it's a bad thing.

However, I've also hear that high humidity with high heat can roughly provide the same effects as training at higher altitude.

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If you take anything to the extremes, like a sauna, yes it will hurt performance. But warmer temperatures such as 75-85F (which in Texas is cool) do increase your RBC compared to training at say 55F all year. Remember just a 2% decrease in body weight due to hydration will cause your performance to suffer.

Any additional stress on your body likely reduces your capacity to increase optimum performance. Heat, altitude, whatever.

However, those stressors will induce a response. So train at altitude to race at altitude. Train in heat and humidity to race in heat and humidity.

For some environmental conditions you can also gain the benefits by using the stressor outside training. E.g. Sleep at altitude, train low. That won't really help you race at altitude, but it can cause some of the adaptations.

Caveat being my science could be out of date (this is from my days as a paramedic studying bio in college and doing mountain rescue in Colorado (10+ Years ago). But I try to keep up and haven't seen anything contradictory.

Not to hijack (this is sort of related) but if "live high, train low" holds true, would it make sense to train "lower" by pumping oxygen into one's pain cave?

I have read that training in extreme heat can cause harmful bacteria to leak from the gut into the bloodstream.

What counts as extreme?

That has been tried by some bicycle track racers, I think at the US OTC in the 1990s - supplemental oxygen during high intensity work on indoor trainers.

I haven't heard much about this since.

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Good question. I read it on the Internet, but seeing as nowadays things on the Internet seem to carry the same weight as scientific studies there must be some truth in it.

I have also read on the Internet that trainimg in heat can have a similar effect effect to training at altitude.

Might give more info in the full text of this study.

http://www.ncbi.nlm.nih.gov/pubmed/19208999

Some more info

http://www.ncbi.nlm.nih.gov/pubmed/?term=Cheung+SS

Study might be of interest

http://jap.physiology.org/content/109/4/1140

Here's one I just found from the book High Tech Cycling:


So live high train low. I guess what I'm really after is live low, train lower, but it appears there's something to it. There's another study where they increase oxygen from 18% to 26% to 60% for high intensity intervals and the results were significantly increased power output.

Cool info - thanks.

I think I have that book (by Ed Burke I think) in a pile of stuff to discard (due to housecleaning - not that it's a bad book) but might take another look at it.

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So you are saying that - all else equal - adding heat does have fitness benefits by increasing RBC, as long as you stay hydrated and replace minerals? Or are the gains not lasting if you go back to cooler training, hence the 2-3 week recommendation?

I am thinking one could see it as a way of spreading out recovery needs. If you run one hour but in enough heat for it to be equal to a harder/longer run, you add the need for 'heat recovery', without increasing the stress on joints, muscles etc. that more/harder running would bring. In this way it would be equal to adding some form of cross training.

Any specifics on the effect of humidity, on its own?

I do all my training in my garage on my trainer. Here in VA, that means sub-20 degrees F in the winter and 100+ almost every day in the summer (with obnoxious humidity to boot).

I prefer the heat. This is probably because I can keep the garage doors open, crank up the jumbo fan, and get airflow.

In the winter it gets warmer throughout the ride to the point where the windows fog. I don't notice any change in HR as a result..but I drink a ton of water when I ride.

I suppose I prefer the heat because probably 75% of my races are June-July-August, and the heat never phases me after training in it so much. I also like to feel warmed up, and in the winter that often takes 20+ minutes.

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Any idea where you read this comparison to altitude training?

So if the goal is a particular training load (in the tss sense) your principle is to create the best conditions to hit that target? Would this rule out for example doing glycogen depleted/low glycogen sessions that some people do?

where I live from April to Mid Nov the outside ambient temp will be high 30's plus. June - Sept high 40's to low 50's (I've seen 57 in my car and when i turned it on all of the electrical systems had shut down and warning came on about the temperature)

In my home where I train indoors, I've an AC set to 18 at the moment and I can barely keep the room in the high 20's / low 30's - and this is our winter (it was 24 today when i went to watch the golf)

The issue with heat, which is compounded by humidity is the ability to put in hard fast efforts.

So last Sept / Oct I could not run much faster than 8.15-30 / mile, head to the Alps last week in Nov, mercury is at freezing and I can run 7-7.15 miles

The issue with the heat / humidity is that the rate limiting step to effort is no longer how hard you can go, but your body working to keep cool - you just can't put in as hard efforts.

the IM I'm training for in June will be 30-35 I think. In June here it will be 45, dropping to 38-40 over night. I'm not sure how well training here will suit prepare me for it, but I'm guessing I might be slightly more acclimated to the heat than people coming from scandinavia.

When you say the quality of your workouts suffer do you mean you get less TSS because you can't put out the same levels of power in the heat?

It is probable heart rate is higher for a given power output due to the heat so it may be that although the power is down the stress on you is just as great or greater which is why some studies have found training in the heat is effective.

It might be interesting to compare TSS based on heart rate to TSS based on power.

I don't think there's any doubt that my HR is higher for a given effort in the heat. Travelling back and forth from the heat to the cold, i can go far faster for a given HR in the cold (fast being relative, but for me it could be as much as 2 or more minutes a mile when the heat and humidity are high)

I think you may have the same or greater stress - its just difficult to do anything that would increase your speed

Not a coach or an expert but here are my thoughts:
1. Training with an elevated core temp has been proven to be beneficial in helping an individual acclimate to racing in the heat. I think it causes some physiological adaptations but more importantly it forces the individual to practice his nutrition program.
2. Acclimation only takes about 6 weeks.
3. Quality of your workouts that day and in the days following may suffer. Especially if not following through with proper hydration/ nutrition.
4. You never want to bonk during a workout. The rest of the days WKOs and the next couple of days will be negatively impacted. During the course of a workout your heart rate and power levels should rise.
5. Make these off season Wko count worry about acclimization later, closer to race day

I will add I was doing passive heat acclimation using a sauna. There was no exercise involved. The amount of time I could tolerate the heat did go up but I don't think that was accompanied by an increase in plasma because I would've seen a RBC increase...and I didn't.