Evaluation of treadmill exercise in a lower body negative pressure chamber as a countermeasure for weightlessness-induced bone loss: a bed rest study with identical twins.
Counteracting bone loss is required for future space exploration. We evaluated the ability of treadmill exercise in a LBNP chamber to counteract bone loss in a 30-day bed rest study. Eight pairs of identical twins were randomly assigned to sedentary control or exercise groups. Exercise within LBNP decreased the bone resorption caused by bed rest and may provide a countermeasure for spaceflight.


BACKGROUND
Bone loss is one of the greatest physiological challenges for extended-duration space missions. The ability of exercise to counteract weightlessness-induced bone loss has been studied extensively, but to date, it has proven ineffective. We evaluated the effectiveness of a combination of two countermeasures-treadmill exercise while inside a lower body negative pressure (LBNP) chamber-on bone loss during a 30-day bed rest study.


METHODS
Eight pairs of identical twins were randomized into sedentary (SED) or exercise/LBNP (EX/LBNP) groups. Blood and urine samples were collected before, several times during, and after the 30-day bed rest period. These samples were analyzed for markers of bone and calcium metabolism. Repeated measures ANOVA was used to determine statistical significance. Because identical twins were used, both time and group were treated as repeated variables.


RESULTS
Markers of bone resorption were increased during bed rest in samples from sedentary subjects, including the collagen cross-links and serum and urinary calcium concentrations. For N-telopeptide and deoxypyridinoline, there were significant (p < 0.05) interactions between group (SED versus EX/LBNP) and phase of the study (sample collection point). Pyridinium cross-links were increased above pre-bed rest levels in both groups, but the EX/LBNP group had a smaller increase than the SED group. Markers of bone formation were unchanged by bed rest in both groups.


CONCLUSIONS
These data show that this weight-bearing exercise combined with LBNP ameliorates some of the negative effects of simulated weightlessness on bone metabolism. This protocol may pave the way to counteracting bone loss during spaceflight and may provide valuable information about normal and abnormal bone physiology here on Earth.
Smith
Scott M
SM
Human Adaptation and Countermeasures Office, NASA Lyndon B. Johnson Space Center, Houston, Texas 77058, USA. scott.m.smith@nasa.gov
Davis-Street
Janis E
JE
Fesperman
J Vernell
JV
Calkins
D S
DS
Bawa
Maneesh
M
Macias
Brandon R
BR
Meyer
R Scott
RS
Hargens
Alan R
AR
D000469:Alkaline Phosphatase / Q000097:blood; D001510:Bed Rest; D015415:Biomarkers / Q000097:blood; D001851:Bone Diseases, Metabolic / Q000517:prevention & control*; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000097:blood; D005080:Exercise Test; D006801:Humans; D008297:Male; D015675:Osteocalcin / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood; D018579:Patient Selection; D011187:Posture; D013026:Space Flight; D016683:Supine Position; D014430:Twins, Monozygotic; D014893:Weightlessness / Q000009:adverse effects*
D015415:Biomarkers; D010281:Parathyroid Hormone; D015675:Osteocalcin; D000469:Alkaline Phosphatase; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium