Fig. 4. Hypothetical trajectories for the amount of voluntary wheel running across a 6-day test period, as implemented in the selective breeding experiment with house mice. (A,B) Examples of greater plasticity in the Selected lines (S; black circles) than in the Control lines (C; gray squares). (C) Similar relative increases in wheel running on a day-to-day basis, but greater absolute increases in the S lines. See text for discussion.