BONE LOSS DURING LONG-TERM SPACE-FLIGHT IS PREVENTED BY THE APPLICATION OF A SHORT-TERM IMPULSIVE MECHANICAL STIMULUS

In long term space flight, the mechanical forces applied to the skelet on are substantially reduced and are altered in character. This reduce d skeletal loading results in a reduction in bone mass. Exercise techn iques currently used in space can maintain muscle mass but the mechani cal stimulus provided by this exercise does not prevent bone loss. By applying an external impulsive load for a short period each day, which is intended to mimic the heel strike transient, to the lower limb of an astronaut during a long term space flight (5 months), this study te sts the hypothesis that the bone cells can be activated by an appropri ate external mechanical stimulus to maintain bone mass throughout prol onged periods of weightlessness. A mechanical loading device was devel oped to produce a loading of the os-calcis similar to that observed du ring the heel strike transient. The device is activated by the astrona ut to provide a transient load to the heel of one leg whilst providing an equivalent exercising load to the other leg. During the EUROMIR95 mission on the MIR space station, an astronaut used this device for a short period daily throughout the duration of the mission. Pre- and po st-flight measurements of bone mineral density (BMD) of the os-calcis and femoral neck of the astronaut were made to determine the efficacy of the device in preventing loss of bone mineral during the mission. O n the os-calcis which received the mechanical stimulus, BMD was mainta ined throughout the period of the flight, while it was reduced by up t o 7% on the os-calcis which received no stimulus. Post-flight, BMD in both the stimulated and non-stimulated os-calcis reduces, the extent o f this reduction however is less in the stimulated os-calcis. For the femoral neck, the mechanical stimulation does not produce a positive e ffect. (C) 1998 Elsevier Science Ltd. All rights reserved.