Received November 25, 2007
Revised January 2, 2008
Accepted after revision February 11, 2008

¹ University of Auckland

^* To whom correspondence should be addressed. E-mail: h.smith{at}auckland.ac.nz.

	Abstract

The aims of this study were to characterize the pattern of voluntary activity of young rats in response to resistance loading on running wheels and to determine the effects of the activity on the growth of six limb skeletal muscles. Male Sprague-Dawley rats (4 weeks old) were housed individually with a resistance running wheel (R-RUN, n=7) or a conventional free-spinning running wheel (F-RUN, n=6) or without a wheel as non-running controls (CON, n=6). The torque required to move the wheel in the R-RUN group was progressively increased and the activity (velocity, distance and duration of each bout) of the two running wheel groups was recorded continuously for 45 days. The R-RUN group performed many more, shorter, and faster bouts of running than the F-RUN group, yet the mean daily distance was not different between the F-RUN (1.3 ± 0.2 km) and R-RUN (1.4 ± 0.6 km) group. Only the R-RUN resulted in a significantly (p < 0.05) enhanced muscle wet mass, relative to the increase in body mass, of the plantaris (23%) and vastus lateralis (17%) muscle, and the plantaris muscle fiber cross-sectional area, compared to CON. Both F-RUN and R-RUN lead to a significantly greater wet mass relative to increase in body mass and muscle fiber cross-sectional area in the soleus muscle compared to CON. We conclude that the pattern of voluntary activity on a resistance running wheel differs from that on a free-spinning running wheel and provides a suitable model to induce physiological muscle hypertrophy in rats.

Key Words: Exercise, Muscle, Rat