Foot forces during typical days on the international space station

Cavanagh, P. R.<sup>1</sup>; Genc, K. O.<sup>1,2</sup>; Gopalakrishnan, R.<sup>3</sup>; Kuklis, M. M.<sup>3</sup>; Maender, C. C.<sup>4</sup>; Rice, A. J.<sup>1</sup>

Affiliations

¹Department of Orthopaedics and Sports Medicine, University of Washington, BB 1065D, 1959 NE Pacific Street, Box 356500, Seattle, WA 98195-6500, USA

²Department of Biomedical Engineering, Case Western Reserve University, Cleveland, USA

³Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH, USA

⁴NASA—Johnson Space Center, Houston, TX, USA

Abstract and keywords

Decreased bone mineral density (BMD) in astronauts returning from long-duration spaceflight missions has been well documented, but the altered mechanical loading environment experienced by the musculoskeletal system, which may contribute to these changes, has not been well characterized. The current study describes the loading environment of the lower extremity (LE) during typical days on the International Space Station (ISS) compared to similar data for the same individuals living on Earth. Data from in-shoe force measurements are also used as input to the enhanced daily load stimulus (EDLS) model to determine the mechanical “dose” experienced by the musculoskeletal system and to associate this dose with changes in BMD.

Four male astronauts on approximately 6-month missions to the ISS participated in this study. In-shoe forces were recorded using capacitance-based insoles during entire typical working days both on Earth and on-orbit. BMD estimates from the hip and spine regions were obtained from dual energy X-ray absorptiometry (DXA) pre- and post-flight.

Measurable loading was recorded for only 30% of the time assigned for exercise. In-shoe forces during treadmill walking and running on the ISS were reduced by 25% and 46%, respectively, compared to similar activities on Earth. Mean on-orbit LE loads varied from 0.20 to 1.3 body weight (BW) during resistance exercise and were ∼0.10 BW during bicycle ergometry. Application of the EDLS model showed a mean decrease of 25% in the daily load experienced by the LE. BMD decreased by 0.71% and 0.83% per month during their missions in the femoral neck and lumbar spine, respectively.

Our findings support the conclusion that the measured ISS exercise durations and/or loading were insufficient to provide the loading stimulus required to prevent bone loss. Future trials with EDLS values closer to 100% of Earth values will offer a true test of exercise as a countermeasure to on-orbit bone loss.

Keywords: Spaceflight; Bone loss; Mechanical loading; Exercise; Countermeasures

Links

DOI: 10.1016/j.jbiomech.2010.03.044

PubMed: 20462584

WoS: 000281534000019

History

Accepted: 2010-03-24

Online: 2010-05-11

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Cited By (4)

Year	Entry
2011	Genc KO. The Effects of Altered Gravity Environments on the Mechanobiology of Bone: From Bedrest to Spaceflight [PhD thesis]. Cleveland, OH: Case Western Reserve University; August 2011.
2014	Ellman R. Skeletal Adaptation to Reduced Mechanical Loading [PhD thesis]. Cambridge, MA: Massachusetts Institute of Technology; September 2014.
2019	Burkhart KA. Understanding Vertebral Fracture Risk in Astronauts [PhD thesis]. Cambridge, MA: Massachusetts Institute of Technology; June 2019.
2010	Holguin N. Low-Level Vibrations Maintain the Intervertebral Disc During Unloading [PhD thesis]. Stony Brook, NY: Stony Brook University; December 2010.