The musculo-skeletal system allows the human body to physically move and exert forces on its environment.
Whereas on Earth the musculo-skeletal system has to support the weight of the body, and the postural bones and muscles are permanently loaded by gravity, this is not the case in weightlessness – here, all physical activities are less demanding, the musculo-skeletal system is unloaded.
As a result exposure to microgravity leads to bone and muscle loss.
Remodelling of the bone structure and/or bone loss during spaceflight occurs at about 1-2% per month and after six months in space astronaut’s osteoporosis symptoms can be compared to those of osteoporosis in elderly women on earth. In microgravity weight-bearing bones are particularly affected and bone mass decreases of up to 20% have been reported after a six month mission. The astronauts returning from long duration space-flights are at risk of fracture and are consequently subject of specific attention and care.
Muscle atrophy results from the lack of demanding activities (no more walking, stairs stepping, lifting of objects,…) and from the unloading of the postural muscles. Muscle loss of 10 to 20 % has been observed on short missions and, if no countermeasures were applied, this could go up to 50% on long duration missions. This might compromise the astronaut’s abilities to perform specific and physically demanding activities during the mission (e.g. extravehicular activities) and after the landing (e.g. emergency egress). This also leads to discomfort: astronauts have very often complained about low-back pain, a subject which is being investigated as being the result of postural muscle atrophy.
Research & Development
Research on bone and muscle loss focuses not only on the understanding of the phenomenon and the study of modifications in the bone structure (EDOS), but also on preventive solutions and rehabilitation procedures. Indeed, astronauts spend a considerable amount of time exercising to counteract bone and muscle loss and maintain their fitness. New methods have been continuously developed and specific fitness training (FWED-PEMS) and monitoring (MARES) devices have been designed. Each of these topics can have a particular positive return on measures for prevention and treatment of similar indications on earth.
Health related topics: Elderly, osteoporosis, long stay at the hospital, confinement to bed, fitness.