Fig. 8:

Example data from one healthy individual showing phase relationships in circadian and ultradian rhythms (less than 24 hr, UR). Records of averages per 20 seconds (A, top to bottom) of the heart’s R-R interval, heart rate variability (HRV), average heart rate (HR), core body temperature (CBT) and locomotor activity (Act). Aligning these reveals that some variables show phase alignment at both circadian and ultradian time scales (e.g. HR and CBT, B), while others display anti-phase relationships at both frequencies (e.g. RR and Act, C). In all cases, ultradian rhythm amplitude is modulated by time of day, so that the circadian-ultradian interaction must be taken into account when comparing phase alignment synchrony across these different physio-behavioral outputs. Data from Cutler et al., 2017.