title: Jumping in simulated and true microgravity: response to maximal efforts with three landing types.
abstract: BACKGROUND
  Exercise is a promising countermeasure to the physiological deconditioning experienced in microgravity, but has not proven effective in eliminating the ongoing loss of bone mineral, most likely due to the lack of high-impact forces and loading rates during in-flight activity. We wanted to determine lower-extremity response to high-impact jumping exercises in true and simulated microgravity and establish if 1-G force magnitudes can be achieved in a weightless environment.
  
  
  METHODS
  Jumping experiments were performed in a ground-based zero-gravity simulator (ZGS) in 1 G, and during parabolic flight with a gravity-replacement system. There were 12 subjects who participated in the study, with 4 subjects common to both conditions. Force, loading rates, jump height, and kinematics were analyzed during jumps with three distinct landings: two-footed toe-heel, one-footed toe-heel, and flat-footed. Gravity replacement loads of 45%, 60%, 75%, and 100% bodyweight were used in the ZGS; because of time constraints, these loads were limited to 60% and 75% bodyweight in parabolic flight.
  
  
  RESULTS
  Average peak ground-reaction forces during landing ranged between 1902+/-607 and 2631+/-663 N in the ZGS and between 1683+/-807 and 2683+/-1174 N in the KC-135. No significant differences were found between the simulated and true microgravity conditions, but neither condition achieved the magnitudes found in 1 G.
  
  
  CONCLUSIONS
  Data support the hypothesis that jumping exercises can impart high-impact forces during weightlessness and that the custom-designed ZGS will replicate what is experienced in true microgravity.
authors.affiliation: Department of Biomedical Engineering, The Cleveland Clinic Foundation, Cleveland, OH, USA. susan_dandrea@afferentcorp.com
authors.forename: Susan E
authors.initials: SE
authors.lastname: D'Andrea
authors.forename: Gail P
authors.initials: GP
authors.lastname: Perusek
authors.forename: Sudhakar
authors.initials: S
authors.lastname: Rajulu
authors.forename: Julie
authors.initials: J
authors.lastname: Perry
authors.forename: Brian L
authors.initials: BL
authors.lastname: Davis
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D007717:Knee / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology; D014893:Weightlessness; D018474:Weightlessness Simulation