Fig. 3. Schematic representation of the in vivo status of thin-filament packing density and spacing in half a sarcomere from a normal pre-flight muscle and in half a sarcomere from an atrophic muscle after a 17-day space flight in humans. Subsequent to atrophy after space flight, short thin filaments increased in number by 9%, and 17% of the thin filaments were lost. These changes summed to produce a 26% decrease in thin filament density in the overlap A-band region (redrawn) (from Riley et al., 2000).