The purpose of this study is to test the hypothesis that muscle fibers are protected from undue atrophy in hibernating dauria ground squirrels (Spermophilus dauricus, Brandt). Muscle mass, fiber cross sectional area (CSA, video analysis) and fiber type distribution (m-ATPase staining) were determined in extensor digitorum longus (EDL) muscle from non-hibernating control animals (Pre-H), from animals who hibernated for one (H1) or two (H2) months, and from animals 2-4days after arousal (Post-H; N=8 each). Muscle wet weight decreased less than body weight in hibernating animals, resulting in a steady increase in muscle-to-body mass ratio (+37% in Post-H compared to Pre-H, p<0.001). In the Pre-H group, Type I (6.3±2.0%) and II (93.7±2.0%) fiber CSAs were 1719±201 and 2261±287μm(2), respectively. There was a tendency (n.s.) of larger CSA of type I in hibernators compared to pre-H. In the Post-H group, fiber CSA and type distribution were not different from Pre-H. We are the first to report data on EDL fiber type distribution and confirm a protective effect that prevents muscle atrophy in spite of prolonged disuse during hibernation in dauria ground squirrels.