Figure 4: (a) mean heart rate (HR). (b) total heart rate variability (HRV total). Box plot illustrations of 14 healthy volunteers are shown. Note the significant differences. The ends of the boxes define the 25th and 75th percentiles with a line at the median and error bars defining the 10th and 90th percentiles. The different measurement phases and points (a–d) are indicated (cf Figure 3).