The Kinematics of Treadmill Locomotion in Space

Locomotion on a treadmill in 0 G will probably remain a centerpiece of NASA's exercise countermeasures programme. This form of physical activity has the potential to cause large bone and muscle forces as well as loading during a period of continuous treadmill exercise. A critical concern is the provision of a treadmill which can approximate 1 G performance in space. At this point, no adequate objective measurements of in-flight treadmill kinetics or of the human response to this activity have been made. Interpretation of the results obtained in the present study is limited by the following: (1) bungee tensions were not measured; (2) ground reaction forces were not measured in parallel with the kinematic measurements; and (3) the instrumentation used to film the astronauts could itself have been affected by microgravity. Despite these shortcomings, what is apparent is that exercise during NASA missions STS 7 and STS 8 resulted in leg motions that were similar to those found during 1 G locomotion on an inclined passive treadmill and on an active treadmill at an even steeper grade. In addition, it was apparent that the majority of the loads were transmitted through the forefoot, and one can surmise that this style of running would result in physiologically significant tensions in the calf musculature and resultant ankle compressive loading. Further speculation regarding limb loading is complicated by the fact that varying amounts of force are transmitted through (1) the treadmill handle and (2) bungee cords that act as a tether. New generations of treadmills are being manufactured that could provide I important information for planners of long-duration space missions. If these types of treadmill are flown on future missions, it will be possible to control bungee tensions more precisely, control for grade and speed, and, most importantly, provide data on the rates and magnitudes of limb loading. These data could then be incorporated into biomechanical models of the lower limb to more fully understand mechanisms of load transmission from distal to proximal structures and to optimize in-flight exercise protocols in such a way that muscle and bone loss could be reduced.