Fatigue-related Characteristics of the Soleus and Extensor Digitorum Longus Muscles in Small and Large Cage-reared Female Rats

Previous studies (Enoka et al., 1984; Enoka and Stuart 1985, Rankin et al., 1984) have indicated that the soleus and extensor digitorum longus muscles of male rats were affected by the size of the cage in which the animal was raised. This observation, along with others (Enoka and Stuart 1983, Dahl and Aas 1981, Yell in and Guth 1970) has raised the question as to the appropriateness of the small cagereared animal as a model for the study of altered-activity effects. To expand the investigation into cage-size effects, some fatigue-related characteristics have been examined in female rat hindlimb muscle. Thirty female Sprague-Dawley rats were raised for 100-135 days in either a small laboratory cage or in one 247X larger. Cage size had no significant effect on 1) force production, 2) fatigue resistance, 3) whole muscle fiber-type composition, or 4) cross-sectional areas of individual fiber-types in either the soleus or extensor digitorum longus muscles of these female rats. Two possible considerations for the lack of effect are firstly that all animals raised in the large cage did not increase their activity level concommitant with the increased cage size. Secondly, there may have been a gender effect attenuating the cage-size effect.