Exercise training

Mice assigned to exercise training groups were subjected to a 4-week protocol of forced treadmill running. The training protocol commenced the Monday after the initial exercise capacity testing with mice exercising 5 days/week (Mon-Fri) at 70 or 75% of the maximal speed achieved during the initial exercise capacity test and an inclination appropriate to the speed (Figure ​(Figure1C).1C). Prior to each training bout, we provided mice with a “warm-up” period of 10 min at 0 m/min and 10 min at 12 m/min to promote exercise protocol compliance and to minimize risk of injury. For comparison between the groups, training intensity was set at 20.8 m/min at a 10° incline for FVB/NJ mice and 16.4 m/min at a 5° incline for C57BL/6J mice, which corresponded to 70% of the maximal speed and the appropriate incline at the calculated speed for each strain during the initial exercise capacity test. In subsequent studies of FVB/NJ mice, mice were exercised only during the day, and in these groups, we implemented a more intensive training protocol to further examine systemic and cardiac adaptations to treadmill running. For this, training intensity was set at 75% of the maximal initial exercise capacity, which corresponded to 22.3 m/min at a 10° incline. In all groups, we progressively increased the workload of the mice, such that they trained for 40 min during week 1, 50 min during week 2, and 60 min during weeks 3 and 4. We chose this progressive intensity protocol to prevent training plateau and to stimulate exercise-induced adaptations (Dudley et al., 1982; Hildebrandt et al., 2003; De Angelis et al., 2004; Massett and Berk, 2005).