Elsevier

Bone

Volume 49, Issue 4, October 2011, Pages 858-866
Bone

WISE-2005: Bed-rest induced changes in bone mineral density in women during 60 days simulated microgravity

https://doi.org/10.1016/j.bone.2011.06.021Get rights and content

Abstract

To better understand the effects of prolonged bed-rest in women, 24 healthy women aged 25 to 40 years participated in 60-days of strict 6° head-down tilt bed-rest (WISE-2005). Subjects were assigned to either a control group (CON, n = 8) which performed no countermeasure, an exercise group (EXE, n = 8) undertaking a combination of resistive and endurance training or a nutrition group (NUT, n = 8), which received a high protein diet. Using peripheral quantitative computed tomography (pQCT) and dual X-ray absorptiometry (DXA), bone mineral density (BMD) changes at various sites, body-composition and lower-leg and forearm muscle cross-sectional area were measured up to 1-year after bed-rest. Bone loss was greatest at the distal tibia and proximal femur, though losses in trabecular density at the distal radius were also seen. Some of these bone losses remained statistically significant one-year after bed-rest. There was no statistically significant impediment of bone loss by either countermeasure in comparison to the control-group. The exercise countermeasure did, however, reduce muscle cross-sectional area and lean mass loss in the lower-limb and also resulted in a greater loss of fat mass whereas the nutrition countermeasure had no impact on these parameters. The findings suggest that regional differences in bone loss occur in women during prolonged bed-rest with incomplete recovery of this loss one-year after bed-rest. The countermeasures as implemented were not optimal in preventing bone loss during bed-rest and further development is required.

Highlights

► Bed-rest results in regional differences in losses of bone in women. ► The greatest effects on bone were seen at the hip and distal tibia. ► Little effect of the countermeasures was seen on bone loss. ► Losses in muscle mass and some changes in body composition were reduced by the exercise countermeasure.

Introduction

In clinical routine the aspects and causes of bone loss are complex. In postmenopausal osteoporosis, for example, there are typically a number of factors contributing to the loss of bone. As such, bone loss causes health care systems worldwide tremendous effort and monetary costs every year, as progressive osteoporosis frequently leads to reduced bone strength, which, when accompanied by falls, can lead to fractures, subsequent immobilisation and further musculoskeletal deconditioning. As part of this, one aspect that can contribute to bone loss is physical inactivity. Bone loss occurs with stroke [1], [2], spinal cord injury[3], [4], and prolonged bed-rest [5], all of which involve some form of inactivity or reduced function. In manned space research bone loss has been detected to be a serious problem. This bone loss can be difficult to prevent with exercise modalities [6], [7], [8] and is presumed to occur as a result of the reduced loading of bone associated with the microgravity environment. Simulated weightlessness, as induced in prolonged bed-rest studies [5], [9], is a valuable tool to evaluate the deconditioning bone occurring in clinical medicine as well as in the manned spaceflight and to define countermeasures to prevent and/or rehabilitate such changes.

Bed-rest studies have to date typically been performed with male subjects. There is of course no guarantee that countermeasures which may, or may not, work for male subjects would necessarily have the same effect on women. The common effects of bed-rest on bone, typically in male subjects, include an increase in bone resorption [10], [11], [12], [13], no significant change [5], [14], [15] or marginal reduction [11], [16], [17], [18], [19], [20], [21] of bone formation, increased calcium excretion [5], [11], [13], and ultimately loss of bone mass and density, predominately from the load-bearing regions of the body [8], [19], [22]. The “Women International Space Simulation for Exploration” (WISE-2005) prolonged bed-rest study was initiated to improve our understanding of the adaptation of female physiology to spaceflight simulation (bed-rest) and to trial countermeasures against the expected deconditioning associated with this simulation in women.

In the WISE-2005 study, in addition to female subjects undergoing strict bed-rest, an exercise countermeasure comprising resistance training and aerobic exercise as well as a high protein and leucine nutrition countermeasure were trialled. As part of our involvement in the WISE-2005 study, we aimed to examine the changes in bone mass at the lower leg (tibia), forearm (radius), hip and lumbar spine and also the effects of the exercise and nutrition countermeasures against these changes.

Section snippets

Bed-rest protocol and subjects

The WISE-2005 study was supported by the European, French, Canadian, German and North American Space agencies (ESA, CNES, Canadian Space Agency, DLR, NASA) and was conducted at the Medes Institute for Space Medicine and Physiology at the Rangueil University Hospital in Toulouse, France (www.spaceflight.esa.int/wise/).

Twenty four healthy female volunteers, 25 to 40 years old participated in this study (Table 1). They were matched according to pre-bed-rest aerobic fitness levels and then randomly

Results

Except for data being unavailable from two subjects in the exercise group at R + 90 and one exercise subject at R + 360, all subjects were measured at all planned points. With the exception of leg sub-region BMD (p = 0.009; whole-body DXA) there was no evidence for differences between groups at baseline for any of the BMD variables (p  0.10; see Table 3, Table 4, Table 5). Data on changes in bone mineral content (BMC) are presented in online supplementary material (ASM Tables 1–3). The results for BMC

Discussion

Contrary to our expectations, the current study found that in women undergoing 60-days bed-rest, an exercise countermeasure combining high-load resistive and aerobic exercise components did not significantly reduce bone mineral density losses. As expected, however, the nutrition countermeasure, which was mainly targeted at muscle metabolism, had no effect on BMD change compared to control. The nutrition countermeasure, however, had no effect on lean and fat mass changes or on muscle CSA at the

Conclusions

In conclusion, the current study examined regional bone loss in women during 60-days bed-rest. Bone loss was greatest at the distal tibia and proximal femur. The pattern of bone loss was similar to that seen in men in other studies in bed-rest, though the data provide some suggestions of sex-differences, for example at the distal radius. The exercise countermeasure (high-load resistive exercise on the flywheel device with lower-body negative pressure treadmill locomotion) implemented provided

Acknowledgments

We thank the 24 women who volunteered for this bed-rest investigation as well as the nurses, staff, and entire research team at the MEDES Space Clinic (Toulouse Rangueil Hospital) for their exceptional care of the subjects during bed-rest and exercise. The study WISE-2005 (Women International Investigation for Space Exploration) was sponsored by the European Space Agency (ESA), the National Aeronautics and Space Administration of the USA (NASA), the Canadian Space Agency, and the French “Centre

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    Funding sources: WISE: sponsored by the European Space Agency (ESA), the National Aeronautics and Space Administration of the USA (NASA), the Canadian Space Agency, and the French “Centre National d'Etudes Spatiales” (CNES). ADOQ: funded by European Commission under Contract QLK-CT-2002-02363, Key Action n°6: “The ageing population and disabilities”, the Swiss government and ESA. DLR: participation of ADOQ group in WISE was funded by the German AeroSpace Center under Contract 50 WB 0522.

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