Einleitung

Heart rate variability (HRV) is the present oscillation of the heart rate. The interest in HRV as a parameter of the parasympathetic and sympathetic influence of the autonomic nervous system on the heart has increased in the last few decades (Kaikkonen et al., 2007). It is known that its influence changes under different conditions such as rest, exercise or mental stress and different body postures (supine, sitting, standing). Results how its influence changes during exercise have been inconsistent (Boettger, 2010, Tulppo et al., 1996). HRV parameters are used as indicators for fatigue or overtraining (Aubert et al., 2003). HRV parameters can be calculated in the time or frequency domain. Standard parameters that are derived from the HRV signal in the time domain are the mean RR interval, the mean heart rate or the square root of the mean squared differences of successive RR intervals (RMSSD) (Task Force, 1996). In the frequency domain, features determined by the power spectral density (PSD) like the power within the low frequency (LF) band (0.04 - 0.15 Hz) or the high frequency (HF) band (0.15 - 0.4 Hz) are common (Task Force, 1996). We investigated the influence of physical activity on HRV in a large-scale study. Running, the chosen physical activity for this manuscript, is a task that has increased its interest in the last few years when looking at the number of recreational athletes participating in Marathons. Running does not require much equipment, can be done almost everywhere and is inexpensive. Here, we examine if and how HRV parameters of the time or frequency domain are changing during one hour of running.