Three possibilities can be distinguished for transferring warmth to the human body. Yet, they are usually not strictly distinct in practice. In a sauna for example, warmth is transferred for the most part by hot air (convection), while the amount of infrared radiation (from the sauna stove and walls) is hardly negligible. Conversely, in the case of infrared cabins, with a design based on a level of air temperature above the indifference temperature (30 – 36 °C), a more than negligible amount of heat is transferred by convection.
When speaking of a warmth treatment for the whole body in a wellness or home setting, usually we mean sauna, steam bath and infrared cabin.
The crucial difference between individual warmth treatments is in the type of temperature regulation each method stimulates. Stated very simply, two different principles or objectives can be identified in warmth treatments of the whole body: stimulation and overheating.
- Sauna treatment
Stimulation
With stimulation, the entire surface of the body is exposed to an air temperature level that is considerably higher than the ‘thermally neutral’ range. Sitting in a saunaat an air temperature of 100 °C for example, heat stimulation causes the body to increase circulation to the skin everywhere in order to cool it. The skin is for the most part in this ‘hotter environment’, so that warmed blood flows from most areas of the skin back to within the body. The body core temperature would rise immediately and quickly, except that the body then protects itself by reducing the flow of blood returning from the skin, i.e. the peripheral arterio-venous shunts (peripheral vessels connecting the tiniest arteries and veins under the skin) are closed. As much as two litres of blood can be ‘lost’ in the skin and is briefly not available for circulation. It may be mentioned here that the vascular system of an adult’s body contains between 70 and 80 ml of blood per kilo of body mass. This equals about 5 or 6 litres of blood. Men usually have about 1 litre more than women, a fact to be attributed to gender differences in height and weight.
Research has been able to demonstrate that the body core temperature does not in fact increase in the sauna during this phase. Yet, depending on physical condition, this protective mechanism can only be maintained for a few minutes due to the heavy strain on the cardio-vascular system. The return flow of blood from the skin must then continue. Once the peripheral AV shunts open, the body core temperature almost jumps to as much as 39 °C. Research therefore recommends sauna treatments for briefly stimulating the vegetative nervous system in the manner advocated by the Kneipp method - in alternation with suitable cold treatments and rest phases. To take best advantage of the positive effects of a sauna (which undisputably exist), you should leave the sauna before the AV shunts open, i.e. before the body core temperature rises drastically. This point is usually reached when you have to struggle to “not give up”. Depending on your physical condition and how you are feeling that day, this period can be from a few minutes to a quarter of an hour. It is not all a set period of time. You need to listen to your body. At lower air temperatures (bio-sauna 50 – 60 °C) and/or high humidity (steam cabinet) this form of temperature regulation varies only by degrees but not in principle.
Overheating
Under this heading all types of warmth treatment to the whole body can be subsumed which aim to raise the body core temperature. A strong distinction still needs to be made among overheating treatments to the whole body.
Wellness centres and home
Mild overheating of the whole body, which can be easily applied for benefit without a medical examination, should remain below the fever range (38 °C and above). The body should be subjected to as little strain as possible and be thoroughly warmed, slowly and gradually, from the outset. The effects caused by the temperature regulation response occur even once the body core temperature has risen slightly. Circulation increases and the supply of nutrients and oxygen to the skin, connecting tissue, muscles and organs improves. The muscles relax, while detoxification and purging are stimulated. The metabolism is accelerated and the immune system is modulated. In this way a great many effects are triggered, some of them non-specific, which can be useful in treating a large number of different ailments. ‘Therapy’ is not the objective of warmth treatment to the whole body in a wellness or home setting, but it is indeed possible to alleviate the symptoms of a variety of ailments. Artificial fever (i.e. temperatures above 38 °C) should always be avoided, as this can pose a certain risk to the user (without medical supervision).
