page_title: Reduced muscle mass, strength and performance in space
section_title: Space Shuttle
hierarchical_section_title: Reduced muscle mass, strength and performance in space / Historical overview / U.S. human spaceflight programs / Space Shuttle
caption_attribution_description: English: Figure 6-8. Percent change in CSA of Type I (slow twitch) and Type II (fast twitch) myofibers in postflight versus preflight muscle biopsies from 8 crewmembers. From reference. [§ 1]Template:Pages
context_page_description: There is a growing research database which suggests that skeletal muscles, particularly postural muscles of the lower limb, undergo atrophy and structural and metabolic alterations during space flight. However, the relationships between in-flight exercise, muscle changes and performance are not well understood. Efforts should be made to try to understand the current status of in-flight and post-flight exercise performance capacity and what the goals/target areas for protection are with the current in flight exercise program.
context_section_description: A variety of investigations related to skeletal muscle function have been completed during the course of the Space Shuttle Program (1981 - 2011).  The most comprehensive of these was a suite of investigations accomplished during the Extended Duration Orbiter Medical Project (EDOMP), which was carried out during 1989 - 1995 with missions of up to 16 days.  Studies most relevant to the risk on which this report focuses include the following:
  DSO 475 - Direct assessment of muscle atrophy and biochemistry before and after spaceflight
  DSO 606 - Evaluating concentric and eccentric skeletal muscle contractions after spaceflight
  DSO 617 - Evaluating functional muscle performance
  The collective specific aim of DSO 477 and DSO 617 was to evaluate functional changes in concentric and eccentric strength (peak torque) and endurance (fatigue index) of the trunk, arms, and legs of crewmembers before and after flight.  LIDO® dynamometer located at the Johnson Space Center and at both the prime and contingency landing sites were used to evaluate concentric and eccentric contractions before and after flight.
  Test subjects in this study exercised during flight for various durations, intensities and numbers of days on the original Shuttle treadmill (figure 6-5) (as opposed to the EDO treadmill, which flew on later Shuttle missions and was the bases for the ISS treadmill) as part of separate in-flight investigations.  Exercise protocols included continuous and interval training, with prescriptions varying from 60% to 85% of preflight VO₂₋ₘₐₓ as estimated from heart rate (HR)  Some subjects had difficulty in achieving or maintaining  their target HR during flight.  The brake (figure 6-5).  A harness and bungee/tether system was used to simulate body weight by providing forces equivalent to an approximate 1-G body mass.  Subjects on this non-motorized treadmill were required to walk and run at a positive percentage grade to overcome mechanical friction.  Study participants were familiarized with the LIDO® test protocol and procedures about 30 days before launch (L-30), after which six test sessions were conducted.  Three sessions were completed before launch (L-21, L-14 and L-8 days) and three after landing (R+0, R+2 and R+7 to R+10 days).
  The muscle groups tested are shown in table 6-1.  Torque and work data were extracted from force-position curves.  Peak-torque, total work, and fatigue index measured in the three preflight test sessions were compared; when no differences were found between sessions, values from the three preflight sessions were averaged and this average was used to compare preflight values with those on landing day and during the postflight period.
  Skeletal-muscle strength was defined as the peak torque generated throughout a range of motion from three consecutive voluntary contractions for flexion and extension.  Eccentric contractions are actions of the muscle in which force is generated while the muscle is lengthening, as opposed to the concentric actions in which the muscle is shortening (contracting) while generating force.  Skeletal-muscle endurance was defined as the total work generated during 25 repetitions of concentric knee exercise, as determined from the area under the torque curve for a complete exercise set.  Work also was compared between the first 8 and last 8 repetitions.  Endurance parameters were measured during concentric knee flexion and extension activity only.  On R+0, significant decreases in concentric and eccentric strength were shown in the back and abdomen when compared to the preflight means (table 6-1).
  Concentric back extension and eccentric dorsiflexion remained significantly less than preflight values on R+7.  Recovery (an increase in peak torque from R+0 to R+7) was demonstrated for the eccentric abdomen and the concentric and eccentric back extensors.
  However, the data depicted in table 6-1 may be somewhat misleading because in some cases there were tremendous differences in strength between crewmembers who exercised during flight versus those who did not.  For example, some crewmembers w
caption: Figure 6-8. Percent change in CSA of Type I (slow twitch) and Type II (fast twitch) myofibers in postflight versus preflight muscle biopsies from 8 crewmembers. From reference.[14]
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