title: Increased wheel-running activity in the genetically skeletal muscle fast-twitch fiber-dominant rats.
abstract: 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 by using genetically fast-twitch fiber-dominant rats (FFDR) and control rats (CR). The rats were divided into four 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 wk and lasted for 7 days. The FFDR showed a lower percentage of type I fibers of the deep portion of gastrocnemius and soleus muscles and a higher percentage of both type IIX fibers of the gastrocnemius muscle and type IIA fibers of the soleus muscle compared with 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 h, 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.
authors.affiliation: Institute of Health Science, Kyushu University, Kasuga, Fukuoka 816-8580, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Suwa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakano
authors.forename: Yasuki
authors.initials: Y
authors.lastname: Higaki
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Nakamura
authors.forename: Shigeru
authors.initials: S
authors.lastname: Katsuta
authors.forename: Shuzo
authors.initials: S
authors.lastname: Kumagai
mesh_terms: D000818:Animals; D001823:Body Composition; D002196:Capillaries / Q000033:anatomy & histology; D005260:Female; D005799:Genes, Dominant; D006651:Histocytochemistry; D006824:Hybridization, Genetic; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology* / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains / Q000235:genetics