The effects of spaceflight on triceps surae muscle torque and cross-sectional area (CSA) were investigated on four astronauts using electrically evoked contractions to by-pass neural control. Muscle twitch characteristics, ankle joint angle–twitch torque relation, frequency–torque relation, tetanic torque and fatigability were assessed before, during and after a 17-day Space Shuttle flight (STS-78). Muscle plus bone cross-sectional area (CSAm+b) was evaluated before and after the flight. Whereas no changes in muscle function were observed during the flight, marked alterations were found during the recovery period. Peak twitch (PTw) and tetanic torques at 50 Hz (PT 50) continued to fall up to the 8th recovery day (R+8) on which losses in PTw and PT 50 were 24.4% ( P
