The running behavior and muscle characteristics associated with voluntary running activity were studied in female Fischer 344 rats after 9 weeks of training in voluntary exercise wheel cages. The exercise wheel employed allowed a load to be added to the wheel axis. The running activity was recorded as the number of rotations every 10 s for 24 h, and the number of running bouts, running duration, running speed and distance run per day were varied. Addition of a load to the wheel axis allowed the running style to be changed, and reduced the running duration and speed in each bout. The voluntary running training was done with no load, 30% per body weight load, and 60% per body weight load, and as treadmill running (40 m/min, 60 min/day) .
In the voluntary training, a difference in the total running distance was observed with increased load. The total distance run under 0%, 30% and 60% load in the voluntary group was about 552, 475, and 438 km, respectively, after training for 9 weeks. As a result of training, the weights of dorsiflexor muscles tended to increase with treadmill running, whereas weights of plantar-flexor muscles increased significantly in the voluntary training groups. In the plantaris muscle, the cross-sectional area of all fiber types was not changed by treadmill training, but in voluntary training, almost every type of fiber was enlarged. Voluntary running with a 30% load increased the cross-sectional area of type I and type ha fibers in the plantaris muscle compared with no load exercise. However, no significant differences in the cross-sectional area of these fibers were observed between 30% and 60% load exercise. The fatigue tolerance of the plantaris muscle improved significantly in all training groups, and the 60% load group showed the highest value.
These results suggest that voluntary loaded running is more effective for muscle enlargement than treadmill training and/or voluntary training with no load.
