The following two graphs are comprised of the same data from 10 individuals, aged 25 years old, who exercised at low-medium intensity for 30 minutes.  The data are presented in bar graph format (A) and scatter plot format (B, where each individual is shown in the same colour) and show the heart rate (in beats per minute, bpm) at Rest and 10 minute intervals throughout the exercise.  Statistical analyses revealed increased heartrate at 20 min compared with Rest (*) and 10 min (#), at 30 min compared with Rest (*), 10 min (#) and 20 min (^), all p<0.05. 

The most variability is seen in the data for which time point?