Fig. 1. Cross section electron micrographs of soleus muscle fibers obtained pre-flight (A) and post-flight (B) from astronaut B of the 17-day STS-78 shuttle flight. The micrographs show the spaceflight-induced atrophy of the myofibrils and the rounding of the mitochondria. The I-bands of representative myofibrils are labeled (I). The amount of glycogen-like particles (the black dots surrounding the fibrils) is similar in both fibers. Scale bar, 0.5µm.