Overview

A Quantitative Test of On-Orbit Exercise Countermeasures for Bone Demineralization Using a Bedrest Analog

Principal Investigator:
Peter R. Cavanagh, Ph.D., D.Sc.

Organization:
The Cleveland Clinic

Dr. Peter Cavanagh and his colleagues are conducting a bed-rest study to better understand the amount of exercise loading that is necessary to reduce bone loss in astronauts during long-duration spaceflight. Volunteers in a 12-week head-down bed-rest study were randomly assigned into one of two groups, an exercise and a non-exercise group. The exercise group participated in an individualized exercise program each day using a vertical treadmill with a one g applied subject load that provided a flight-like simulation of the treadmill exercise that is performed in space. The goal of the exercise prescription is to replace the daily load stimulus in one g which was measured during entire days of free living prior to bed rest. In order to compare the changes between the exercise and non-exercise group members, measurements of bone mineral density, muscle volume and strength are taken at the beginning and the end of the 12-week period. Bone metabolic markers are also collected.

In addition to providing an answer if exercise can adequately protect the body from bone and muscle loss during spaceflight, the data will be helpful to understand the importance of exercise for prevention and treatment of bone diseases such as osteoporosis.

NASA Taskbook Entry

Technical Summary

Bed rest is an excellent analog for the study of on-orbit musculoskeletal changes that occur during long-duration spaceflight. Our novel approach involved quantifying typical daily loads to the lower extremities in selected free-living volunteer subjects who were moderate exercisers and planning individual exercise prescriptions based on daily load stimulus theory. Subjects were randomized to control or exercise groups and confined to 6-degree head-down bed rest in the General Clinical Research Center at the Cleveland Clinic Foundation (CCF) for 12 weeks.

During this time, the exercise group underwent individualized daily exercise programs in the unique Zero Gravity Locomotion Simulator at CCF designed to replace their daily mechanical load stimulus experienced during free living. Dual Energy X-Ray Absorptiometry, Magnetic Resonance Imaging and Quantitative Computed Tomography scans were conducted at the start and end of bed rest to assess variations in bone mineral density, changes in muscle volume and regional changes (cortical vs. trabecular) in bone. Strength measurements were collected pre- and post-bed rest, and urinary and serum markers of bone resorption and formation were also assessed. Dietary intake sufficient to maintain constant body weight with a balanced intake of macro- and micronutrients was planned and supervised by a registered dietician, and a physician was available 24 hours a day to attend to any medical needs.

A rehabilitation program was offered to subjects in the eight weeks following bed rest. The experiment should provide a categorical answer to the question of whether intermittent load replacement can adequately protect the musculoskeletal system against hypokinetic osteopenia and muscle atrophy and may open a new era in individualized exercise countermeasure planning.

This study has been relocated to the NASA Flight Analogs Research Unit at the University of Texas Medical Branch in Galveston for completion. All data reported here were collected at the CCF.

Earth Applications

The information obtained as a result of this study will provide further insight into the role of skeletal loading in bone loss during long-duration spaceflight, and knowledge gained from this research will thereby contribute to a better understanding of the importance of exercise for the development and maintenance of bone strength among humans living in Earth gravitational fields. Knowledge in this area is crucial to the treatment of bone disease for which exercise may or may not be an effective intervention.

This project's funding ended in 2009