As mentioned before,

perceived situational stressors are associated with higher RRs (Grossman 1983). Recently, however, Anderson and Chesney (2002) reported an association between an inhibited breathing pattern and sustained stress (perceived stress over the past month). According to these authors an inhibited breathing pattern might explain the contribution of chronic stress to the development learn more of hypertension. Comparison of the RR values of the sample of subjects in the present study with those of the healthy subjects suggests a decreased RR in subjects prolonged fatigue, in accordance with the findings of Anderson and Chesney (2002). No studies are available that evaluate the validity of HRV and RR measurements to determine fatigue. Gurbaxani et al. (2006) correlated

questionnaires and biological variables with case classifications of chronic fatigue syndrome. Among other conclusions, they established that the SF-36 correlated highly with the case classification. They further state that biological correlates of chronic fatigue syndrome (e.g. heart rate and HRV) require further investigation. In the present study, HRV and RR measurements did not correlate significantly with either CIS scores or scores on the subscale PN of the SHC. This means that HRV and RR cannot be used to determine fatigue. This does not mean, however, that these subjects with fatigue complaints do not have lowered HRV and/or a higher or lower RR compared to their see more healthier states before they became fatigued. This should be confirmed in a study with an appropriate design. A limitation of the present study should be taken into account with

respect to its comparability to other studies that measure HRV. The Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology 1996) published guidelines for HRV measurements, which specify that 5-min recordings using frequency domain analyses are Carbachol preferred for short-term HRV measurements. In this study, the HRV parameters, SDNN and RMSSD, were calculated using time selections of 7 min for reclining and 9 min for cycling. Because the Lifestylemanager software that was used in this study requires 300 data points to calculate SDNN and RMSSD, data selections of more than 5 min were needed for subjects whose heart rates were below 60 beats/min. This practical consideration was the reason for this deviation from the guidelines. Conclusions We conclude from our findings that measurements of time-domain HRV (SDNN and RMSSD) and RR are reproducible in this sample of fatigued participants. The results of the repeated measurements do not differ much from each other and the measurement device is capable of discriminating between subjects.