Pitfalls in the interpretation of spectral analysis of the heart rate variability during exercise in humans

Abstract

The recent use of spectral analysis of the R-R interval variability to assess the autonomic drive during exercise has produced inconsistent results. The purpose of this study was to assess whether the spectral components of the R-R interval variability reflect different mechanisms at rest and during exercise. Autoregressive spectral analysis of the electrocardiographic and breathing signals was performed in 11 healthy young men at rest and during incremental cycle ergometry. The amplitude of respiratory sinus arrhythmia, i.e. the absolute power of the high frequency spectral component, fell at the onset of exercise, consistent with a reduction in cardiac vagal activity. Conversely, the normalized power of the high frequency component, (i.e. the percentage of R-R interval variance due to the respiratory sinus arrhythmia) increased with increasing work rates. The low frequency spectral component of the R-R interval variability, which when expressed in normalized units is believed to reflect cardiac sympathetic activity, was no longer detectable in severe exercise when the adrenergic drive is known to be elevated. In conclusion, autoregressive spectral analysis of the R-R interval variability does not adequately reflect the autonomic changes that occur during incremental exercise. In particular, the evidence indicates that as the cardiac vagal tone falls with increasing levels of exercise, a greater percentage of the residual power of the high frequency component may be due to non-neural mechanisms.

Heart rate variability is related to training load variables in interval running exercises

“…The lowest exercise intensity in the present study was 50 % of the VO2max of untrained women, based on knowledge of the approximate intensity at which vagal activity diminishes (Casadei et al 1995;Perini et al 1990;Tulppo et al 1998). After 3.5 km or 7.0 km of exercise at such intensity, a fast increase of HFP and TP almost to the pre-exercise levels was detected already during the first recovery minute after exercise cessation.…”

“…SDNN) methods, HRV is greatly diminished during exercise when compared to rest (Arai et al 1989;Casadei et al 1995;Macor et al 1996;Perini et al 1990;Pichon et al 2004). HRV decreases as a function of exercise intensity, almost disappearing at exercise intensities exceeding 50-60% of VO2max (Hautala et al 2003;Tulppo et al 1998) or the ventilatory threshold (Yamamoto et al 1991).…”

“…It is known (Casadei et al 1995;Nakamura et al 1993;Perini et al 1990;Tulppo et al 1998) that when the intensity of exercise exceeds 50-60 % of VO2max, vagal contribution to HR regulation diminishes, and finally disappears. Based on that, the lowest intensity chosen was 50% of vVO2max.…”

“…One possible explanation for the LFP increase after the exercises may be due to alterations in baroreflex sensitivity. Baroreflex sensitivity is known to be inhibited during high-intensity exercise and to recover after the cessation of exercise (Berntson et al 1997;Casadei et al 1995). The similarity of LFP and TP recovery patterns during immediate recovery also suggests that during recovery from high-intensity exercise, in contrast to rest, TP may consist mostly of low frequency variation and therefore, indicates overall changes in autonomic modulation rather than changes in vagal modulation.…”

Muscle Metaboreflex Contribution to Sinus Node Regulation During Static Exercise

“…In this context, it is of note that total RR-interval variance was not significantly changed from rest during exercise, probably because HR values attained during SLE were not so dramatic. Thus, in our study, extremes of stimulation of the sinus node did not occur, allowing us to emphasize the strengths of the spectral analysis technique 24 rather than their limitations, at variance with other studies 25,26 that used various protocols of dynamic exercise that drastically reduced HR variability. Obviously, large interindividual differences in total power or in DC noise present at rest may persist during exercise, making it necessary to use normalized units to better assess the distribution of power in defined spectral components.…”