Journal of Applied Physiology
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J Appl Physiol (September 6, 2002). doi:10.1152/japplphysiol.00295.2002
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Articles in PresS, published online ahead of print September 6, 2002
J Appl Physiol, 10.1152/jap.00295.2002
Submitted on April 5, 2002
Accepted on September 2, 2002

Increased wheel-running activity in the genetically skeletal muscle fast-twitch fiber dominant rats

Masataka Suwa1, Hiroshi Nakano2, Yasuki Higaki3, Tomohiro Nakamura4, Shigeru Katsuta5, and Shuzo Kumagai1*

1 Institute of Health Science, Kyushu University, Kasuga, Fukuoka, Japan
2 Department of Human Development, Nakamura Gakuen University, Jonan-ku, Fukuoka, Japan
3 Department of Preventive Medicine, Saga Medical School, Saga, Saga, Japan
4 Department of General Education, Osaka Institute of Technology, Asahi-ku, Osaka, Japan
5 Graduate School of Integrated Science and Art, University of East Asia, Shimonoseki, Yamaguchi, Japan

* To whom correspondence should be addressed. E-mail: shuzo{at}ihs.kyushu-u.ac.jp.

The purpose of the present study was to investigate whether genetic differences in muscle histochemical characteristics were related to the voluntary wheel-running activity level using genetically fast-twitch fiber dominant rats (FFDR) and control rats (CR). The rats were divided into 4 groups; sedentary CR (Sed-CR), wheel-running CR (WR-CR), sedentary FFDR (Sed-FFDR), and wheel-running FFDR (WR-FFDR). Wheel-access was started at age 9 weeks and lasted for 7 days. The FFDR showed a lower percentage of type I fibers of the deep portion of M. gastrocnemius and soleus, a higher percentage of both type IIX fibers of the M. gastrocnemius and type IIA fibers of the M. soleus than CR. A higher capillary density and smaller fiber cross-sectional area were also observed in FFDR. The daily running distance in WR-FFDR was higher than in WR-CR for each 7 days. The total running distance for 7 days in WR-FFDR was 3.2 fold higher than in WR-CR. On day 7 of the 7-day test, the total number of active 1-min intervals for 24 hours, the average rpm when they were active, and the maximum rpm for any single 1-min period in the WR-FFDR were significantly higher than in the WR-CR (1.5, 2.9, and 2.0 fold, respectively). These results suggest that mechanical or physiological muscle characteristics may thus affect the wheel-running activity level.




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