title: Musculoskeletal effects of 5 days of bed rest with and without locomotion replacement training.
abstract: OBJECTIVE
  The present study evaluated the effectiveness of a short and versatile daily exercise regime, named locomotion replacement training (LRT), to maintain muscle size, isometric strength, power, and endurance capacity of the leg muscles following 5 days of head-down tilt (HDT) bed rest.
  
  
  METHODS
  10 male subjects (age 29.4 ± 5.9 years; height 178.8 ± 3.7 cm; body mass 77.7 ± 4.1 kg) performed, in random order, 5 days of 6° head-down tilt bed rest (BR) with no exercise (CON), or BR with daily 25 min of upright standing (STA) or LRT.
  
  
  RESULTS
  Knee extensor and plantar flexor cross-sectional area (CSA) were reduced by 2-3 % following bed rest (P < 0.01) for CON and STA, yet maintained for LRT. Knee extensor isometric strength (MVC) decreased by 8 % for CON (P < 0.05), was maintained for STA, and increased with 12 % for LRT (P < 0.05). Plantar flexor MVC remained unaltered during the study. Maximum jump height declined (~1.5 cm) for all conditions (P < 0.001). Neural activation and knee extensor fatigability did not change with bed rest. Bone resorption increased during BR and neither LRT nor STA was able to prevent or attenuate this increase.
  
  
  CONCLUSIONS
  LRT was adequate to maintain muscle size and to even increase knee extensor MVC, but not muscle power and bone integrity, which likely requires more intense and/or longer exercise regimes. However, with only some variables showing significant changes, we conclude that 5 days of BR is an inadequate approach for countermeasure assessments.
authors.affiliation: Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany, Edwin.Mulder@dlr.de.
authors.forename: E
authors.initials: E
authors.lastname: Mulder
authors.forename: G
authors.initials: G
authors.lastname: Clément
authors.forename: D
authors.initials: D
authors.lastname: Linnarsson
authors.forename: W H
authors.initials: WH
authors.lastname: Paloski
authors.forename: F P
authors.initials: FP
authors.lastname: Wuyts
authors.forename: J
authors.initials: J
authors.lastname: Zange
authors.forename: P
authors.initials: P
authors.lastname: Frings-Meuthen
authors.forename: B
authors.initials: B
authors.lastname: Johannes
authors.forename: V
authors.initials: V
authors.lastname: Shushakov
authors.forename: M
authors.initials: M
authors.lastname: Grunewald
authors.forename: N
authors.initials: N
authors.lastname: Maassen
authors.forename: J
authors.initials: J
authors.lastname: Buehlmeier
authors.forename: J
authors.initials: J
authors.lastname: Rittweger
mesh_terms: D000328:Adult; D001510:Bed Rest / Q000009:adverse effects*; D015444:Exercise; D005081:Exercise Therapy / Q000379:methods*; D006801:Humans; D018476:Hypokinesia / Q000628:therapy*; D007537:Isometric Contraction; D008124:Locomotion; D008297:Male; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000502:physiology*