Isokinetic Force and Work Capacity After Long-Duration Space Station Mir and Short-Term International Space Station...

INTRODUCTION: The effects of long-duration (213.0 ± 30.5 d) stays aboard the orbital station Mir and short-term (∼10 d) spaceflights aboard the International Space Station (ISS) on the joint torques of various muscles and work capacity of knee extensors were studied in male cosmonauts.METHODS: Joint torque and muscle endurance testing was performed 30 d before and 3-5 d after a spaceflight, using a LIDO^® Multi-Joint Isokinetic Rehabilitation System (USA).RESULTS: Greater postflight changes in maximal joint torque were observed for back, knee, and ankle extensors compared with flexors, and the difference was especially clearly seen after long-term spaceflights. The decrease in maximal joint torque of hip extensors substantially varied, being the greatest in voluntary concentric movements in a low-velocity high-force mode at angular velocities of 30 and 60° · s^-1 (by 16 and 13%, respectively) and the lowest in high-velocity modes at velocities of 120 and 180° · s^-1 (by 9 and 11%, respectively). Muscle work capacity was inferred from the gradient of declining muscle force produced in a series of rhythmic voluntary concentric movements and was found to decrease after both short- and long-term spaceflights. The area under the muscle contraction curve decreased to a greater extent and in all regions of the curve after long-term spaceflights. The fatigue index averaged 0.90 ± 0.03 at baseline and remained much the same, 0.90 ± 0.04, after a short-term spaceflight. However, after a long-duration spaceflight, the fatigue index increased 14.1%.DISCUSSION: The finding that the contractile functions and work capacity of muscles decrease more after long-term than after short-term spaceflights in spite of the physical training program of a certain type gave grounds to assume that physical training employed in long-term spaceflights were insufficient to simulate the daily mechanical load that the cosmonauts had before a spaceflight.Koryak YA