If I train in sauna for something like Maraton des Sables, can this have side effects on the long run? What about steam room? By training, I mean stretching, push-ups, squats, abs - aprox 10 reps every 30 or 60 seconds. Of course the time spent in will depend on everyone's stamina.
This is going to sound counterintuitive, but hear it out.
If you want to get better at performing in the heat, train in the cold.
First and foremost training in the cold is a more rigorous workout. Every aspect of improved performance depends on your body becoming more proficient and efficient. The more effective your body becomes at exertion, the less resources it needs to do the same effort. The way the body responds to heat and cold are not terribly different in terms of thermal dynamics. You want your body to be able to move heat, and the more heat it can move the better you are at withstanding heat or cold.
Adding heat load increases risk, and does not work the same as adding weights to a bar. The thermal environment of a sauna versus a desert are too dissimilar to be effective. Indeed I'd surmise the result to be negative. Running in desert heat involves a lovely ballet of air currents you do not find in a sauna. The type of heat is dramatically different - no sun in the sauna.
To improve your body's ability to handle heat, raise it through more strenuous effort. Sprints instead of hours long runs, for example. If possible, do these in colder temperatures, not warmer ones. In the long run, pun unintended, improving your body's native thermal transfer and heat dynamics such as breathing as well as decreasing the time and effort it takes to cross the same distance will serve you better, and without the added risk of heat stroke and decreased rebound and recovery capacity.
If you still feel you must train in a hotter climate, wear layered clothing. Indeed in my experience wearing more clothing rather than less in the desert reduced water loss. While I don't fully understand it, the body does seem to sweat more when more skin is exposed. I suspect it is a dynamic local calculation in order to redirect heat to where it can be whisked away. You might be surprised to learn a lot of desert racers wear full length clothing during the race. Some use "space blankets" even.
Drinking a smaller amount of water will not improve your ability to operate on lower amounts of water. The body needs the same amount of water for the same expenditure of effort. Water is also essential to recover, and going into a deficit will increase your recovery time, thus decreasing your overall training time and increasing the risk of overtraining. Indeed you want to drink often while training to develop the habit. Drink like you should in the desert, not less. How much you drink in the desert will be determined initially by your habit of drinking water. If you habitually drink less, you will automatically drink too little in the event and suffer for it. Learn to drink when it is less critical, not when your life is on the line.
It is a matter of biochemistry, not practice. What you seek is to expend less effort, only in that way can you stand a chance at lower water requirements. Even then, the difference will be negligible. When it comes to sweating how much you sweat is up to your body. Some people are profuse sweaters and others are not.
Generally the more effort is required, the higher the sweat level becomes. The phrase "without breaking a sweat" exists for a reason.
You also need to learn what nutrients and electrolytes your body needs and when. How much do you plan to carry? How much will you decide you really need after the first hour? ;) These are questions you need to answer before the event.
So why train in the cold? In addition to the increased effort, it stresses the body to transfer heat. In a hot climate the body is trying to push heat out into a hot environment. It has no options. In cold it is trying to move heat around the body to get where it needs to be. This thermal dynamic improves your ability to shed heat. When I was in the desert, those who came from hot climates always did worse than those from cold ones when it came to handling exertion in the heat. Sure, they didn't view the heat the same way, but they didn't handle it as well either. Maybe they didn't respect it, or maybe they were physiologically unprepared for it, I don't know. Just that they didn't handle it as well.
All that said, your other preparation will be more important, and is often overlooked. Consider what you need to do to protect your body on the dunes. Heavy sunscreen. This includes clothing as well as pastes. Sand. Lots and lots of sand. Ever run with sand in your shoes? Know how to handle that? These will be greater impacts than you realize. Many think the heat is their greatest opponent in the desert. They are wrong. You need to learn to move and run while minimizing the entire environment. Direct sunlight is your opponent, sandy shoes are your opponent.
I know it sounds crazy, but take it from someone who spent crazy amounts of time in deserts while ending to do high intensity activities. You won't be defeated because you didn't train in the heat. You'll be defeated because you didn't plan for the rest of the environment. Run in leggings, paste, full body protection, gaiters, sunglasses, gear on, etc. Do these things not because they might make you better, but to create the habit of wearing these items as extensions of your body.
Cheers, and good luck.
Apart from the strange looks you would get from other users(unless sauna is private). I can't imagine this would be overly useful. I suspect you would need to come out of the sauna long before it would be really useful for heart and lungs.
I have trained for hot overseas marathons in the past. Admittedly through a Uk summer. I trained by wearing thermal top and legging. Ie overdressing
My race was in Greece and it worked for me. Although I guess Marathon de Sables would be hotter.
I didn't know about Maraton des Sables, so I had to google it source.
Based on the information gathered, I don't think that any of those exercises will help your preparation for that competition.
The goal of the competition is to be able to withstand the heat with as less water as possible. Sauna is basically steam; so, while it might dehydrate you, it doesn't give your body the same experience as what'll be experienced in the actual competition. If you have a way to simulate the dry heat, that would have been your best option; if not, sauna seems like the next best thing.
As for the bodyweight exercises, I don't think those are necessary as they wouldn't help your body conserve its usage of water, a highly needed requirement in the contest.
What exercise to perform in it? None, except being able to withstand the heat as long as possible with limited water consumption. You probably need to consume less water daily as the contest approaches too, so that your body begins to adjust to the new water requirement.
Good luck on that and do let us know how it works out :)