title: Electrically Stimulated Antagonist Muscle Contraction Increased Muscle Mass and Bone Mineral Density of One Astronaut - Initial Verification on the International Space Station.
abstract: BACKGROUND
  Musculoskeletal atrophy is one of the major problems of extended periods of exposure to weightlessness such as on the International Space Station (ISS). We developed the Hybrid Training System (HTS) to maintain an astronaut's musculoskeletal system using an electrically stimulated antagonist to resist the volitional contraction of the agonist instead of gravity. The present study assessed the system's orbital operation capability and utility, as well as its preventative effect on an astronaut's musculoskeletal atrophy.
  
  
  METHODS
  HTS was attached to the non-dominant arm of an astronaut staying on the ISS, and his dominant arm without HTS was established as the control (CTR). 10 sets of 10 reciprocal elbow curls were one training session, and 12 total sessions of training (3 times per week for 4 weeks) were performed. Pre and post flight ground based evaluations were performed by Biodex (muscle performance), MRI (muscle volume), and DXA (BMD, lean [muscle] mass, fat mass). Pre and post training inflight evaluations were performed by a hand held dynamometer (muscle force) and a measuring tape (upper arm circumference).
  
  
  RESULTS
  The experiment was completed on schedule, and HTS functioned well without problems. Isokinetic elbow extension torque (Nm) changed -19.4% in HTS, and -21.7% in CTR. Isokinetic elbow flexion torque changed -23.7% in HTS, and there was no change in CTR. Total Work (Joule) of elbow extension changed -8.3% in HTS, and +0.3% in CTR. For elbow flexion it changed -23.3% in HTS and -32.6% in CTR. Average Power (Watts) of elbow extension changed +22.1% in HTS and -8.0% in CTR. For elbow flexion it changed -6.5% in HTS and -4.8% in CTR. Triceps muscle volume according to MRI changed +11.7% and that of biceps was +2.1% using HTS, however -0.1% and -0.4% respectively for CTR. BMD changed +4.6% in the HTS arm and -1.2% for CTR. Lean (muscle) mass of the arm changed only +10.6% in HTS. Fat mass changed -12.6% in HTS and -6.4% in CTR.
  
  
  CONCLUSIONS
  These results showed the orbital operation capability and utility, and the preventive effect of HTS for an astronaut's musculoskeletal atrophy. The initial flight data together with the ground data obtained so far will be utilized in the future planning of human space exploration.
authors: Department of Orthopedics, Kurume University School of Medicine, Kurume, Fukuoka, Japan; Division of Rehabilitation, Kurume University School of Medicine, Kurume, Fukuoka, Japan.
authors: Naoto
authors: N
authors: Shiba
authors: Division of Rehabilitation, Kurume University School of Medicine, Kurume, Fukuoka, Japan.
authors: Hiroo
authors: H
authors: Matsuse
authors: Division of Physical Therapy, Fukuoka International University of Health and Welfare, Okawa city, Fukuoka 8318501, Japan.
authors: Yoshio
authors: Y
authors: Takano
authors: Department of Orthopedics, Kurume University School of Medicine, Kurume, Fukuoka, Japan.
authors: Kazuhiro
authors: K
authors: Yoshimitsu
authors: Department of Orthopedics, Kurume University School of Medicine, Kurume, Fukuoka, Japan; Division of Rehabilitation, Kurume University School of Medicine, Kurume, Fukuoka, Japan.
authors: Masayuki
authors: M
authors: Omoto
authors: Department of Orthopedics, Kurume University School of Medicine, Kurume, Fukuoka, Japan; Division of Rehabilitation, Kurume University School of Medicine, Kurume, Fukuoka, Japan.
authors: Ryuki
authors: R
authors: Hashida
authors: Department of Mechanical and Control Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka, Japan.
authors: Yoshihiko
authors: Y
authors: Tagawa
authors: Department of Mechanical and Control Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka, Japan.
authors: Tomohisa
authors: T
authors: Inada
authors: Space Environment Utilization Center, Japan Aerospace Exploration Agency, Tsukuba, Ibaraki, Japan.
authors: Shin
authors: S
authors: Yamada
authors: Space Environment Utilization Center, Japan Aerospace Exploration Agency, Tsukuba, Ibaraki, Japan.
authors: Hiroshi
authors: H
authors: Ohshima
mesh_terms: D000328:Adult; D018480:Astronauts; D015519:Bone Density / Q000502:physiology; D001862:Bone Resorption / Q000517:prevention & control*; D004551:Elbow Joint / Q000502:physiology; D004558:Electric Stimulation; D004599:Electric Stimulation Therapy / Q000379:methods*; D004576:Electromyography; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009133:Muscular Atrophy / Q000517:prevention & control*; D009929:Organ Size; D016059:Range of Motion, Articular / Q000502:physiology; D013026:Space Flight; D019415:Torque; D014893:Weightlessness