Ask the Expert: What If an Instructor Won’t Allow Air-Conditioning in a Spinning Class?

As we approach summer and its increasing temperatures, we’re reminded of the Nelly song “Hot In Here.” While we’re not encouraging students to take off their clothes in class like Nelly suggests, we are suggesting that instructors keep the AC or the fans running. This article, originally posted in 2013, describes the dangers associated with teaching an indoor cycling class without air-conditioning or fans. This is a serious subject. Some instructors still buy into that “macho” image of “sweat until you drop” without understanding the dangers. This article provides the ACSM guidelines as well as the physiology of thermoregulation.

An ICA member asked what I thought about an instructor he knew who teaches without air-conditioning or fans in her Spinning class and asked about the potential dangers for the students. 

I know of an instructor who likes to teach her Spinning class without air-conditioning. Could you explain the danger as well as the health issues that this could bring to the class?

This is an excellent question. Every instructor should be aware of the guidelines for temperature and ventilation in an indoor cycling room and should understand the physiology of how the body regulates temperature and the potential dangers of excessive heat.

It’s distressing to hear that any instructor would encourage working out without fans or air-conditioning. To this instructor, it is probably a hallmark of machismo to bear with the challenge of heat and excessive sweating, though it really is nothing more than ignorance and ego. This line of thinking is antiquated, backward, and potentially very dangerous. All you have to do is Google “exercising in the heat” and you will find thousands of articles that describe how dangerous it can be.

It’s not uncommon for people to suffer heat-related illnesses, dizziness, or even cardiac arrest when their body temperature gets too high. While these are possible indoors, it is still fairly rare. More likely in an indoor cycling studio is the simple fact that heat will cause a reduction of exercise performance. Studies have found that mental and physical performance are adversely affected by heat and dehydration. This earlier onset of fatigue may be due to a thermal limit to exercise performance acting as a protection mechanism to prevent potential damage to the body by limiting further heat production1. Sensation of effort is increased and the individual feels like she is exercising harder than she actually is. It is clear that an instructor who denies students the benefits of cooler air and ventilation is actually impairing the students’ workout. This is despite the fact that they may sweat more and feel greater fatigue.













Physiology: How the body regulates heat

Body temperature is automatically regulated through a process called thermoregulation. Our bodies are able to balance heat production and heat loss to keep a relatively stable body temp of 98.6°F/37°C. When we exercise, the body temp rises. Our bodies convert chemical energy from food into mechanical energy (which is what allows us to move) but 25% of this energy is lost to heat. The higher the intensity of the workout, the higher the body temperature becomes.

Exercising in average conditions (indoors or out) allows the body to adjust to the increase in body temperature. But, as the external temp increases, the body cannot radiate heat from the surface of the skin as effectively. If the ambient temperature exceeds 98 degrees, there can be a net gain in heat from the environment, potentially raising the body temp even more2

Our body’s cooling mechanism is the ability to sweat—millions of sweat glands on the surface of the skin secrete liquid (H2O) which evaporates into a gas form. This process of evaporation lowers the temperature of the skin which, in turn, cools the blood and ultimately the body.

As the body releases fluids through the skin via sweat, it can quickly reduce blood volume due to fluid loss. A lower blood volume requires that the heart pump even faster to deliver the blood to the working muscles, which in turn increases body temperature. This vicious cycle may lead to serious dehydration and is a very risky situation if the body isn’t hydrated and cooled down quickly.

Extremely warm and humid temperatures can quickly overwhelm your body’s cooling system—particularly when the air is not circulating, as is the case in many studios with inadequate ventilation.

The heat index is an even more important metric to look at than just the ambient temperature.

Heat Index
The National Oceanic Atmospheric Administration (NOAA) developed a Heat Index Chart3 to provide guidance about exercising in the heat. The heat index was created to gauge what air temperature and relative humidity “feel like” to the human body. A heat index of 105, for example, means that the environment “feels like” 105 degrees, even when the ambient temperature is only 90, 95, or 100 degrees. As humidity increases, the heat index increases. The body cannot cool itself as effectively at higher humidity levels because evaporative sweat is less efficient.

“Caution” should be used when exercising in 80°F heat index and above; “extreme caution” when 91°F and above; it is “dangerous” when 104°F and above; and you put yourself in “extreme danger” when 124°F and above.

A cycling studio that approaches 85°F (30°C) with a humidity of 70% will translate to a heat index of 92 degrees. According to the Heat Index Chart, “extreme caution” must be taken when exercising at this temperature, and heat cramps and heat exhaustion are possible. A crowded cycling room without fans or AC and filled with warm bodies can easily reach into the mid-80s or -90s, even if the outside air is much cooler.

ACSM facility guidelines
The following are the ACSM guidelines for temperature and ventilation provided for health and fitness facilities.4

Facilities should provide all physical activity spaces with sufficient air circulation and fresh makeup air (i.e., outside air) which will allow the facility to maintain air quality, room temperatures, and humidity at safe and comfortable levels during times of physical activity.

Air circulation is one of the most critical elements when designing and operating a health/fitness facility. When a room is filled with members and users exercising at a moderate to high intensity, the heat and humidity load increases dramatically. This can place an increased level of heat stress on the members and users and may result in dehydration, heat exhaustion, heatstroke, or (in rare instances) cardiovascular emergencies. In addition to the increased heat load that can result from improper air circulation, a risk of poor air quality exists than can expose members and users to airborne pathogens that can increase the risk of respiratory disorders or other airborne illnesses. Facilities can provide sufficient air circulation by taking into consideration the following factors:

* Maintain relative humidity at 60% or lower in all physical activity spaces. Ideally, a relative humidity level of 50% or lower is the desired goal, but maintaining levels below 60% is necessary.

* Maintain air temperature for all physical activity areas between 68 and 72 degrees F (20 and 23 degrees C). The key is to maintain these temperature ranges whether the room is empty or fully occupied by members and users who are engaging in moderate to vigorous physical activity. This guideline refers to the fact that the heating, ventilation, and air-conditioning (HVAC) system within the facility should have the capability to adjust airflow to meet the demands of each space.

The Spinning® and Indoor Cycling Studio
Mad Dogg Athletics and Spinning defers to the ACSM and ACE facility guidelines for temperature and ventilation of Spinning rooms. However, I feel that many indoor cycling rooms should be held at a temperature that is slightly lower than the 68–72 degrees F (20–23 degrees C) recommended by ACSM. In my role as a master instructor for Spinning for twelve years, I visited well over a hundred indoor cycling studios, and many of the studios are often smaller than the aerobics or other group fitness studios. Oftentimes they are an afterthought, especially in the older facilities, and are converted from a racquetball or squash court, which can mean there is insufficient ventilation. 

Intense indoor cycling sessions can raise the body temperature higher than many other forms of group exercise classes. Multiply that by 15, 20, or more participants and you can see how these smaller rooms packed to the maximum with sweaty bodies can become very hot and stuffy in a very short time. For this reason, a baseline temperature several degrees below the standard guidelines is warranted to allow for the expected increase once the class gets going.

Ample ventilation is extremely important. Providing fans is essential to the comfort and safety of students, although how many are available and where they are directed is a potential firestorm of discontent among students! (Another topic for another article!)

We are approaching late-summer right now (in the northern hemisphere, that is) and there have been record heat waves here in the US. It’s still hot inside the cycling studio. However, it isn’t only in the heat of summertime when one must be concerned about working out in a room that is too hot. Exercise studios, especially crowded Spinning or indoor cycling rooms, can get especially hot even in the middle of winter if there is improper ventilation and cooling. Therefore, this topic is not just for summer.

It is incumbent on the facility to provide an environment that is safe and comfortable for participants in regards to temperature and ventilation. Instructors who deny students air-conditioning or fans are putting their students at potentially serious risk while reducing the effectiveness of their workout.


1. Exercise, Heat, Hydration, and the Brain. R.J. Maughan, S.M. Shirreffs, and P. Watson. Journal of the American College of Nutrition. October 2007.

2. Exercising in the Heat. Dr. Stephen D Ball, Ph.D., Nutrition and Exercise Physiology, University of Missouri Extension. Online article,

3. National Weather Service, Online information on the heat index. 

4. ACSM Health/Fitness Facility Standards and Guidelines, ACSM (Human Kinetics, 2007), page 35

ACSM Health/Fitness Facility Standards and Guidelines, by Stephen J. Tharrett, Kyle J. McInnis, James A. Peterson, Human Kinetics, 2007, page 35

ACSM position stand on fluid replacement guidelines 

Are supporters of excess heat and sweat in yoga classes just full of hot air Dan Pitko, Elephant Journal, July 29, 2011. 

Exercising in the Heat. Dr. Stephen D Ball, Ph.D., Nutrition and Exercise Physiology, University of Missouri Extension. 

Exercise, Heat, Hydration, and the Brain. R.J. Maughan, S.M. Shirreffs and P. Watson. Journal of the American College of Nutrition. October 2007.

Foods, Nutrition and Sports Performance; C Willimas and J.T. Devlin, ed. (1994), pp 147-178


  1. This piece, while physiologically informative, seems to me to be rather one-sided, simplistic, and [to be blunt] a bit fear-mongering. It cites extreme conditions which obviously should be avoided as common sense. But it creates no middle ground between a comfortable workout and such unhealthy, extreme conditions. Surely there is, or can be, with care, such middle ground. And it is EXACTLY in that middle ground that athletic training yields RESULTS. Just as one example, those training for outdoor activities do not have the option of artificial climate control during such activities or events. To some degree, the adage that the harder the conditions the more one gets out of training is certainly true. And I find it rather odd that a piece with such grave concern over body overheating doesn`t say a single word about the importance of HYDRATING during a class. Most instructors who fuss over fans and room climate will happily smile through an entire class where nobody touches a bottle. I constantly remind people in my classes to drink, and if conditions are hotter than normal I will shut off music and stop a class if people do not at least pick up bottles and make me THINK they are drinking. Drinking sufficient water is infinitely more significant for body temperature regulation than using fans. Thank you for considering an alternative perspective.

    1. Author

      interesting perspective IRA. I probably should have mentioned hydration, I’ll give you that, but even hydration can’t combat excessive temps in a studio. I have written a lot about proper hydration in other articles, however.

      Just this past weekend, I was listening to a cycling training podcast (TrainerRoad) on the subject of training in the heat. They were adamant that you simply cannot put out the required effort in the heat (power output) to achieve desired adaptations, combined with the dangers of heat exhaustion, so it’s not worth it. Riders who are trying to achieve training objectives should either modify their training (such as training indoors or riding in very early hours) or modify their expectations of their training. You can’t get what you want out of the effort in excessive heat.

      Indoors, participants expect the studio to control these factors—and they should. So I stand by everything I said 100%.

      It stands to reason that you should hydrate well—regardless of the temperature and especially in higher temps.

      1. Thank you for the thoughtful reply. I think that a fundamental distinction here is that we have quite different approaches to training. You appear to be prioritizing the goal, a certain level of achievement, the ‘destination’ if you will. You are saying [if I interpret correctly] that the desired achievement might not be gotten in hotter conditions, ergo those conditions should be mitigated. But I emphasize the PROCESS when I train- the ‘journey’. Of course there is a conceptual destination; in fact, there are many in any given class- so many hundred turns of the pedals, so many minutes at unsustainable pace, whatever. But my philosophy is that making it harder to achieve those things is what drives people to the levels that transcend their current states of fitness; and whether one actually REACHES the desired achievement is irrelevant [who CARES if one can do 200 turns in three minutes at a certain resistance??]. It`s purpose is just to create a higher work level. Extending that idea to it`s logical endpoint yields what I consider the primary philosophy of training: if one can DO something, it is obsolete for getting better. It is the goals that are just out of reach that draw one on to work just that little bit harder and close the gap between actualization and potential. And harder conditions to a point are integral to that idea. But again I emphasize, whatever parameters there are here for differing theories of training certainly do not exceed safe and extreme conditions. I am not an advocate of so-called ‘extreme’ sports- diving to absurd depths or climbing to extreme heights without air tanks for example . There`s a very identifiable difference in my opinion between pushing one`s limits and attempting to defy physiology. I might add in closing that, contrary to what some may want to think for their own philosophical convenience, I am also not attempting to display ‘machismo’, nor am I ignorant or excessively egotistical. Rather, I am dedicated to helping people deal with a fundamental truth that most everyone seeks to avoid or sidestep: one simply does not get better at comfortable levels. Thanks again for your time and consideration.

        1. Author

          I absolutely agree with your summary: one simply does not get better at comfortable levels. I have written workshops on how, when, and why we (as instructors) should inspire our participants to go beyond their comfort zones.

          Athletes need to acclimate for the environment they will be competing in, that’s for sure, but who are our typical participants? Our riders aren’t training to be firefighters nor race a 100 miler in the desert (if they are, they aren’t likely in our classes). So the point of this article is to stress that when you increase the temperature, you simply cannot improve performance—your output, your work, is lower than if you were in a more controlled cooler environment.

          The discomfort might be due to the heat and a higher heart rate, making you sense that you are working harder, but you cannot physically put out as much. As a result, the physiological adaptations you seek will not occur—therefore you are doing your riders a disservice.

          Maybe if I provide an examples with numbers.

          Suppose this rider has a LT (lactate threshold) of 170 and an FTP (functional threshold power) of 200.

          She attempts to do the same high-intensity workout on different days at different temperatures. Other variables are held constant (time of day, what she ate, humidity, sleep, etc.).

          The workout requires three 2- minute intervals at 120% of FTP and three 4-minute intervals at 105% of FTP. This requires pushing oneself beyond one’s comfort zone. It’s a very hard workout.

          Test #1: 68 degrees. (ACSM recommendation)
          During the 4-minute intervals, she can maintain FTP and successfully completes both sets of intervals. HR rises to 175 (above LT) in both interval sets and RPE was about 9, “very hard.” She was totaly breathless on the 2-minute ones.

          Test #2: 95 degrees.
          She completes the three 2-minute intervals and was able to maintain 105% FTP for the first one, but RPE was 10. On the next two, her power drops to 95–100% of FTP. HR is elevated to close to 190, near her maximum.

          For the 4-minute intervals, she can’t get close to 105% FTP, and over the 4 minutes, output steadily drops to well below FTP. But HR stays elevated at 185–190. By the third one, she says, “no way” and just rides easy, at 60% FTP. Her HR only drops to 170 and stays there, even with Zone 2 (FTP) effort.

          That is a very realistic scenario when heat is high.

  2. Great information thanks! Any recommendations as to how I can get the instructors to turn the fans back on?

    1. Author

      1. show them this post
      2. show management this post.
      3. Any members who don’t like fans because they think they’ll burn more calories from sweating? Show them this post as well!

      I don’t like fans directly on me, so I understand that others don’t as well. But there should be no-fan zones AND full fan zones. Our studio doesn’t get that hot.

  3. I work in YMCA four fans two in the right, two in the left side. I sometimes have windows just get some fresh air. One student tell me before do not open fan next to her due to catch cold. I respect her not open fan. How many fans can I approx open prevent person catching cold? I open six windows in the class. The building used to be private school before converted to YMCA.

    1. I have exercised for many years and most gyms did not use fans. I have noticed increasing use of fans and ac in spinning and other cardio classes. Now people in stretch and yoga classes are requesting fans. I personally find this very uncomfortable. My muscles cramp and I have discontinued attending certain classes. This has evolved over the years and is reflective of the overuse of air conditioning in everyday life. I’m looking for a gym without air conditioning but don’t expect to succeed.

      1. Author

        there is a tremendous difference between cardio classes like indoor cycling that raise the heart rate and elevate body temps and classes like yoga and stretching. They aren’t even comparable when talking about temperature.

        Everything written in this article is directed at cycling classes, not yoga. And yes, every cycling class should be temperature regulated/ventilated so that temps do not get too high.

        Can it get too cold? Too many fans? Sure, but that is a different story and is not dangerous, though it might be uncomfortable. I, for one, hate fans directly on me. I get chilled very quickly. I would not come back if there were constant fans and very low temps. Every club/studio should provide a section of the room without direct fans. But, those areas still get the benefit of ventilation and not excessive heat.

        1. “Can it get too cold? Too many fans? Sure, but that is a different story and is not dangerous, though it might be uncomfortable.”

          Really? I got two sinus infections from 68 (studio claimed, I brought a digital thermometer it was really 66) and blasting fans. Nowhere to hide in these rooms.
          They make sure no station is further away than one bike distance from a fan. I sweat a lot because of how I am and I have a fairly high FTP. Finally, had to drop them. Setting the environment at this temp w/ fans seems to be the unfortunate norm in the two places I tried. What I don’t understand is keeping the environment this way in the Fall/Winter. I think most people in these rooms for whatever reason (from my observation – don’t like to sweat) prefers this environment and is a popular consensus. Now they have a web article to prove it! Why I found this article today? Fall, raining, 50F outside. Inside: 65 (claimed 68) fans blasting. Whore my hoodie and a base layer. Been feeling chills this evening.

  4. Heat is certainly a problem in an indoor cycling room but my question concerns the elevated carbon dioxide levels in the room. When air conditioning is off or broken not only is the air temperature unable to be cooled but there is insufficient ingress of oxygenated air. CO2 is already elevated in strenuous exercise so what are the downsides to the high CO2 levels in the room? High altitude training for free? Prolonged Anaerobic exercise. ?When its really bad, in my experience, it can cap your exertion level.

    1. Author

      Hi Steve,
      even if the a/c is not working and a room gets hot, in most cases in commercial buildings, the fans are likely still on and there should still be ventilation. In order for CO2 to build up in a room to a dangerous level, it would have to be COMPLETELY sealed off. This would not be the case in a commercial building—per any country’s building codes.

      Your question is a good one because CO2 levels do increase somewhat indoors, especially in gyms…but it would be rare that it’s enough to be an issue. A room might feel stuffy, and yes, your performance might go down, but that is more likely due to the heat rather than a build up of CO2. Nevertheless, you might suggest to management that the HVAC (heating, ventilation, and AC) of the club be examined to improve air flow even when the AC is off or broken.

      (FYI, I asked my husband for help on this question because he is a general contractor and understands ventilation in buildings really well!)

      A high altitude training benefit is not derived from an increase in CO2. What happens at elevation is that the partial pressure of oxygen is reduced—where I live at 8,000 feet in Colorado, it’s about 25% less than at sea level. It’s the pressure differential that causes O2 to move from the lungs to the blood and from the blood to the cells across the capillary wall. CO2 moves the opposite direction. The benefit from high-altitude living is that the body adapts so it can extract more O2 from the blood to make up for the reduced pressure. An increased presence of CO2 has no effect on this adaptation (which, by the way, is why so-called altitude masks DO NOT WORK!!)

      Inhaling CO2 is not what causes anaerobic metabolism; it’s the breakdown of glycogen that has CO2 as a byproduct.

      Hope that helps!

  5. I have one rider that wants the fan directed to her face while Spinning and I noticed after class she hardly is sweating. What is the disadvantage of not sweating while working? Does sweating relate to weight loss or it does not play a role in weight loss?

    1. Author

      This is an excellent question, Josephine! We will answer that in full very soon in our Ask the Expert segment. But basically, sweat is the body’s means of cooling, as it evaporates, it lowers the temperature of the skin. But sweat in and of itself is not a measurement of how hard you are working. And it play no role in weight loss…except in the very short term by reducing blood volume (via the H2O that is lost through sweat). After a very sweaty workout, especially in the heat, you can lose a pound or two of body weight, but it’s 100% water loss, and therefore dehydrating. Once you drink water, you gain it back! So no, sweat does not equal a good workout, nor does it equal weight loss. Stay tuned for the physiology on that!

  6. Interestingly, I have almost the opposite problem. We have individual AC set-ups for all the studios and they’re very responsive. Good so far, right? My classes are all mid morning so I frequently get to the gym and find someone (I’m assuming it has to be a member) has cranked the AC waaay down and left it and I walk into a room that’s frequently below 60 degs. I then have to turn the heat on to bring the room up to something a bit warmer just so the air *conditioning* will kick in during class as well as the cooler temp.

    Not a practical issue as I’m always there well ahead of time to get a bit of a workout in as well as doing all my checks and whatnot, but it takes a fair bit of explaining my rationale on the rare occasions that a class member comes early also. Now I can bamboozle them with more technical sounding terms like % relative humidity

    1. Author

      yes, that can be an issue too! Me, I have a very narrow range of comfort–I’m easily too cold or too hot! But I’d rather start off chilly knowing it’s going to warm up. And, you can always add clothing…you can’t always take off more! 😉

      Still, too cold can keep people from coming or from enjoying the workout.

  7. I had it backwards. That’s a great analogy and citation. Thank you.

  8. 25% is lost as heat. So we are approximately only 75% efficient.

  9. is (if I recall correctly) only about 25% which means that
    – only about 25 % of the energy produced by metabolism is turned into mechanical power where as
    – about 75% of the energy is “lost” in chemical conversion and predominatly dissipated as thermal energy.

    Somebody with more scientific physiological background than me might better comment.

Leave a Reply

Your email address will not be published. Required fields are marked *