Victor S. Schneider

Calf muscle area and strength changes after five weeks of horizontal bed rest

Nine male volunteers participated in a 10 week meta bolic study in which subjects underwent 5 weeks of ambulatory control and 5 weeks of complete horizontal bed rest. Bed rest is a model commonly used to simu late space flight. The changes in muscle area and strength of the calf dorsiflexors and plantar flexors were measured before and after bed rest using magnetic resonance imaging (MRI) and a Cybex II dynamometer. The muscle area of the plantar flexors (gastrocnemius and soleus) decreased 12%, whereas the muscle area of the dorsiflexors was not significantly decreased. The maximal muscle strength of the plantar flexors de creased 26%; the muscle strength of the dorsiflexors was not significantly decreased. These results, which demonstrate differential muscle atrophy and a larger loss in strength relative to muscle area, have important implications in the development of exercise counter measures to be impiemented during space fiight. The results also have implications for patients who have severe orthopaedic disorders and must be bed rested for long periods of time, and for persons who are voluntarily inactive (a large number of the elderly).

Changes in intervertebral disc cross-sectional area with bed rest and space flight

Study Design. We measured the cross-sectional area of the intervertebral discs of normal volunteers after an overmight rest; before, during, and after 5 or 17 weeks of bed rest; and before and after 8 days of weightiessness. Objectives. This study sought to determine the degree of expansion of the lumbar discs resulting from bed rest and space flight. Summary of Background Data. Weightlessness and bed rest, an analog for weightlessness, reduce the mechanical loading on the musculoskeletal system. When unioded, intervertebral discs will expand, increasing the nutrtional diffusion distance and altering the mechancial properties of the spine. Methods. Magnetic resonance imaging was used to measure the cross-sectional area and transverse relaxation time (T2) of the intervertebral discs. Results. Overnight or longer bed rest causes expansion of the disc area, which reaches an equilibrium value of about 22% (range 10–40%) above baseline within 4 days. Increases in disc area were associated with modest increases in disc T2. During bed rest, disc height increased approximately 1 mm, about one-half of previous estimates based on body height measurements. After 5 weeks of bed rest, disc area returned to baseline within a few days of ambulation, whereas after 17 weeks, disc area remained above baseline 6 weeks after reambulation. After 8 days of weightlessness, T2, disc area, and lumbar length were not significantly different from baseline values 24 hours after landing. Conclusions. Significant adaptive changes in the intervertebal discs can be expected during weightlessness. These changes, which are rapidly reversible after short duration flights, may be an important factor during and after long-duration missions.

Spinal bone mineral after 5 weeks of bed rest

SummaryPatients put at bedrest for medical reasons lose 1–2% of spinal bone mineral per week. Losses of this magnitude during even shortterm space flights of a few months would pose a serious limitation and require countermeasures. The spinal bone mineral (L2–L4) was determined in 6 healthy males (precision=2%) before and after 5 weeks of complete bed rest. Only one individual had a significant loss (3%) and the −0.9% mean change for the 6, was not significant (P=0.06). The average negative clacium balance during the 5 weeks was 4 g or 0.36% of total body calcium, similar to that reported in other bed-rest studies. Spinal bone loss, however, in healthy bed-rested males is significantly less than reported for bed-rested patients, suggesting that a large loss of spinal bone mineral does not occur during space flight missions lasting 5 weeks or less.

Can the adult skeleton recover lost bone

The loss of bone mineral with aging and subsequent development of osteoporosis is a common problem in elderly women, and as life expectancy increases, in elderly men as well. Space flight also causes bone loss and could be a limiting factor for long duration missions, such as, a Mars expedition or extended occupation of a space station. Before effective countermeasures can be devised, a thorough knowledge of the extent, location, and rate of bone loss during weightlessness is needed from actual space flight data or ground-based disuse models. In addition, the rate and extent that these losses are reversed after return from space flight are of primary importance. Although the mechanisms are not likely to be the same in aging and space flight, there are common elements. For example, strategies developed to prevent disuse bone loss or to enhance the rate of recovery following space flight might have direct applicability to clinical medicine. For various reasons, little attention has been given to recovery of bone mass following space flight. As a prelude to the design of strategies to enhance recovery of bone, this paper reviews published literature related to bone recovery in the adult. We conclude that recovery can be expected, but the rate and extent will be individual and bone site dependent. The development of strategies to encourage or enhance bone formation following space flight may be as important as implementing countermeasures during flight.

Prevention of space flight induced soft tissue calcification and disuse osteoporosis

This paper emphasizes the devastating effects of displacement of calcium during space flight, due to increased bone turnover.

Musculoskeletal Adaptation to Space Flight

Clinical and research data from U.S. and Russian short and long duration space missions have clearly demonstrated that humans living and working in space have muscle, connective tissue, and skeletal atrophy when appropriate countermeasures are not used. The atrophy may be continuous or intermittent and possibly progressive until a new homeostatic set point is reached. These changes are manifested in the way the body conserves and activates the muscles, and manages the calcium and other minerals that normally are stored in the skeleton. Loss of total body muscle volume and strength causes decreased muscle force output and early muscle fatigability. In parallel to the muscle atrophy in gravity-dependent muscles and at muscle-bone insertion sites, bone matrix and bone mineral is destroyed leading to possible osteoporosis and the loss of bone strength and increased bone fracture risk. The increased excretion of urinary calcium and phosphorus (bone mineral constituents) may increase the risk for renal stones or dehydration with hypercalcemia. These medical consequences from the musculoskeletal atrophy may cause crew members health problems or limit exploration space mission success. Biomedical research on the International Space Station is helping to maintain the health of astronauts and to develop appropriate countermeasures to protect the musculoskeletal organs of crew members during space flight, when landing on distant planets, and on their return to Earth. This chapter reviews current medical data on how the musculoskeletal organs adapt to space flight and the results of countermeasures to maintain Earth normal bone and muscle form and function.

Bone Loss in Space Flight and Countermeasures

Before manned space flight, it was known that immobilization of patients for extended periods, such as for fracture repair to treat the paralysis of polio myelitis or paraplegia, often resulted in weakened and atrophic bones. Although the problems related to reduced gravitational forces on the musculoskeletal system were recognized, the full extent of the changes was not known. Therefore, studies were planned and conducted by the emerging American and Soviet space programs to determine the extent of, and potential harm associated with, bone loss that might occur during space flight.