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The purpose of this study was the development and fabrication of the instruments and hardware necessary to quantify the vertical impact forces (Fz) imparted to the space shuttle passive treadmill during human locomotion in a three dimensional zero-gravity environment. The shuttle treadmill was instrumented using a force plate (Kistler) to measure vertical impact forces. The current passive treadmill system employs a harness/bungee device as a means to restrain an astronaut in zero G. Force links (Kistler) were employed to measure the bungee cord loading. The hardware was designed so that it would meet crash loading requirements as written in the JSC-22803 manual for experiments flying in the Reduced Gravity Aircraft (KC-135). The impact force and bungee cord data was collected and analyzed using a biomechanics performance analysis system (Adel Corporation).

To verify that the instruments and hardware were functional, they were tested in the Anthropometry and Biomechanics Laboratory (ABL) at the Johnson Space Center. The KC-135 reduced gravity aircraft was used to determine if the system could operate successfully in a three-dimensional zero-gravity environment. It was found that the vertical impact forces could be quantified in a one-G and zero-G environment using the force plate, and through use of the force plate and/or bungee instrumentation, a subject's one-G weight could be replicated in zero-G by adjusting the bungees to elicit the proper load. The magnitude of the impact loads generated in one-G on the shuttle treadmill for the given walking, jogging and running velocities (1.1 G, 1.7G, and 1.726 respectively) were not observed in the zero-G environment. However for the higher zero-G jogging and running velocities (3.5 mph and 5.0 mph) greater than 1 G loads were seen (1.2G and 1.5G). Thus the issue becomes "How much impact is enough?".

As a part of the system, it was necessary to incorporate a data collection instrument. A biomechanics analysis system (Ariel Performance Analysis System, ADI Inc. Corporation, 6 Alicante, Trabuco Canyon, CA 92679) served as the data collection device (Figure 12). Using this system, data was acquired from all data input channels at a rate of 250 samples/channel/second. A ruggedized hardware cabinet had to be obtained to encase this system and the other associated electronics equipment before they could fly on the KC-135 aircraft. A KC-135 floor-to-cabinet interface plate, a back plate, and cabinet insertion plates had to be designed and created for mounting the equipment inside the hardware cabinet . The cabinet back plate and the hardware insertion plate are shown in Figure 13a. The assembled hardware cabinet system is depicted in Figure 13b.


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