title: Foot-ground reaction force during resistive exercise in parabolic flight.
abstract: BACKGROUND
  An interim resistance exercise device (iRED) was designed to provide resistive exercise as a countermeasure to spaceflight-induced loss of muscle strength and endurance as well as decreased bone mineral density. The purpose of this project was to compare foot-ground reaction force during iRED exercise in normal gravity (1 G) vs. microgravity (0 G) achieved during parabolic flight.
  
  
  METHODS
  There were four subjects who performed three exercises (squat, heel raise, and deadlift) using the iRED during 1 G and 0 G at a moderate intensity (60% of maximum strength during deadlift exercise). Foot-ground reaction force was measured in the three orthogonal axes (x, y, z) using a force plate, and the magnitude of the resultant force vector was calculated (r = square root(x2 + y2 + z2)). Linear displacement (LD) was measured using a linear transducer. Peak force (Fpeak) and an index of total work (TWi) were calculated using a customized computer program. Paired t-tests were used to test if significant differences (p < or = 0.05) were observed between 1 G and 0 G exercise.
  
  
  RESULTS
  Fpeak and TWi measured in the resultant axis were significantly less in 0 G for each of the exercises tested. During 0 G, Fpeak was 42-46% and TWi was 33-37% of that measured during 1 G. LD and average time to complete each repetition were not different from 1 G to 0 G.
  
  
  CONCLUSIONS
  Crewmembers who perform resistive exercises during spaceflight that include the movement of a large portion of their body mass will require much greater external resistive force during 0 G than 1 G exercise to provide a sufficient stimulus to maintain muscle and bone mass.
authors.affiliation: Wyle Laboratories, Life Sciences Systems and Services, Houston, TX 77058, USA. slee1@ems.jsc.nasa.gov
authors.forename: Stuart M C
authors.initials: SM
authors.lastname: Lee
authors.forename: Kendall
authors.initials: K
authors.lastname: Cobb
authors.forename: James A
authors.initials: JA
authors.lastname: Loehr
authors.forename: Daniel
authors.initials: D
authors.lastname: Nguyen
authors.forename: Suzanne M
authors.initials: SM
authors.lastname: Schneider
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D015444:Exercise; D005528:Foot / Q000502:physiology*; D006801:Humans; D018472:Hypogravity; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D010806:Physical Education and Training; D013026:Space Flight; D014160:Transducers, Pressure; D016474:Weight-Bearing / Q000502:physiology*