Almost 60 years ago Selye introduced "the general adaptation syndrome", where he investigated several internal and external stressors that may disturb the homeostatic balance. Among these stressors was, for example, strenuous exercise. The general adaptation syndrome is made up of three stages: Alarm reaction, stage of resistance, and state of exhaustion (Selye 1956). In athletic training, which can be considered as a mainly physical stress model, the overload principle is widely used. The overload training principle is intended to disturb the homeostasis of the body through the physical stress of a training session (alarm reaction). During the subsequent recovery phase, the physical capacity is recovered, possibly to a higher level than before the training session (resistance or adaptation phase). This process needs coordination of various systems that are appropriate to counteract the threats to homeostasis. The autonomic nervous system, including both the parasympathetic and sympathetic pathways, is highly responsible for this regulation of homeostasis. In the beginning of stress research, investigations concentrated on responses of the endocrine system to different stressors. During late 20th century studies on usage of autonomic cardiac indices as an indicator of autonomic modulation have increased. In addition to clinical cardiac autonomic tests in laboratory, more practical methods for real-life situations have been developed. Heart rate and heart rate variability have been recorded during rest, in an active orthostatic test, or as a response to some other known challenge. As levels of heart rate variability indices and their responses are highly individual, it is extremely important to build a large database of an athletes' own values. While building this kind of individual database, sources of stress should be also recorded. For international level athletes, the physiological training stress is commonly the most important stressor, but there can be others, too. When analyses are done from data collected during wakefulness, many different issues may have effects on autonomic modulation. Issues like the time of day can be standardized, but e.g. thoughts are more difficult to control. Therefore, cognitions may play a role in these recordings. When recording heart rate variability during nocturnal sleep, we have somewhat freedom of external disturbance, and are able to analyze the most important period of recovery, too. During rest, the parasympathetic activity is normally high and this is reflected in high values of heart rate variability indices. As a response to overload training, diminished values of heart rate variability are typically seen. After suitable rest or easier training, recovery to high values can be found. Responses to different stressors are dependent not only acutely on the power and duration of the stressor, but it is also possible that the stress effects are sustained or even cumulated for a longer period of time. An example of one skier's follow-up figure shows variation of so-called "recovery index", where high values are reflecting good recovery and lower values reflect stress responses after hard training sessions and/or races (Figure 1). It should be reminded that it is a good thing, when reduced values of heart rate variability is found after hard training sessions or periods. This is the phenomenon targeted, but as important is that the level of heart rate variability is recovered after easier training or rest. In conclusion, nocturnal HRV may be used to estimate changes in autonomic modulation during the recovery phase from acute endurance exercises. These methods can be utilized in individual follow-ups of stress management or athletic training programs. --- The hosting University of Jyväskylä is planning to publish conference proceedings "Science and Nordic Skiing III". In case you are interested in this publication please contact the editors (Anni Hakkarainen anni.s.j.hakkarainen@jyu.fi) to become registered for the book.
© Copyright 2015 3rd International Congress on Science and Nordic Skiing - ICSNS 2015. 5-8 June 2015, Vuokatti, Finland. Veröffentlicht von University of Jyväskylä; University of Salzburg. Alle Rechte vorbehalten. / Übersetzt mit https://www.DeepL.com/Translator