HEAT, SWEAT & VENTILATION

WHAT WE KNOW:

We know how heat will raise heart rate. We also know that increasing heart rate has nothing to do with extra power output; it isn't due to your physical effort to harder. It simply means your body has to work harder at the same power output to dissipate heat. Why? Because excessive heat is not a desirable thing – your heart rate increases so it can send more blood more quickly to the skin for the evaporative cooling effects of sweat and convection. This higher heart rate can translate to not being able to work hard enough, reducing your ability to train, reducing your potential power output.

And, contrary to what your heart rate monitor might indicate, this higher heart rate does not translate to an increase in caloric expenditure.

Heat Index

We know that the Heat Index (HI) is an index that combines air temperature and relative humidity in an attempt to determine the human-perceived equivalent temperature – in other words how hot it feels. The result is also known as the “felt air temperature” or “apparent temperature”. For example, when the temperature is 32 degrees C with very high humidity, the heat index can be about 41 degrees C.

Body Cooling

The human body normally cools itself by perspiration or sweating. The evaporation of water needs heat that is absorbed from the body to yield water vapour. However, a higher relative humidity reduces the evaporation rate because of the higher vapour content. This results in a slower heat removal from the body, hence the overheat sensation.

The following information has been taken directly from the INDOOR CYCLING ASSOCIATION Guidelines:

Physiology:

The human body temperature is 96-99 degrees F (98.6F/37C is only an average). 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 about 98 degrees F. 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 temp 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 well. If the ambient temperature exceeds 98 degrees, there can be a net gain in heat from the environment, potentially raising the body temp even more. The body's cooling mechanism is the ability to sweat – millions of sweat glands on the surface of the skins secrete liquid. As this liquid (H20) evaporates into a gas form, the process lowers the temperature of the skin. This in turn cools the blood and ultimately the body.

As the body releases fluids through the skin (sweat), it can quickly reduce blood volume due to fluid loss. There is a very real potential for dehydration if it is not replaced. Dehydration in turn leads to a higher body temperature and a higher heart rate, which in turn increases body temperature. This 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.

ACSM facility guidelines

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

- 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.

The Spinning^® and Indoor Cycling Studio

Many cycling studios are often smaller than the group fitness studios. Oftentimes they are an afterthought, especially in the older facilities, and are converted from a 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 exercisers, 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 a degree or two 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, however, how many are available and where they are directed is a potential firestorm of discontent among students!

Summary

We are approaching summer right now. It's 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 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.

Regardless of personal preferences the science is clear:

It is incumbent on the health & fitness facility to provide an environment that is safe and comfortable for participants in regards to temperature and ventilation. An instructor who denies students air conditioning or fans is putting his or her students at potential risk while also reducing the potential of their workout.

The resources for this information are below:

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, PhD, Nutrition and Exercise Physiology, University of Missouri Extension 
3. National Weather Service, Online information on the heat index. http://www.crh.noaa.gov/lmk/?n=noaaexcessiveheat#heatindex 
4. ACSM Health/Fitness Facility Standards and Guidelines, ACSM (Human Kinetics, 2007), page 35