The ISS is scheduled to have a six-person crew by the spring of 2009. All six crewmembers will be required to complete a daily exercise regimen that includes exercise on a treadmill. Operational considerations prevent the exclusive use of the existing TVIS to meet the requirement. Therefore, to accommodate the increased crew, a second treadmill has been proposed for the ISS.
Hypothesis: Locomotion on the T2 will have similar lower extremity joint kinematics as locomotion at similar speeds in 1-G.
Subjects completed locomotion at each speed under two external load (EL) conditions. During the light EL condition, the bungee load was adjusted to approximately 55% of body weight (BW). During the heavy EL condition, the bungees were adjusted to approximately 80% of BW. Appropriate EL levels were obtained by adding carabiner clips in series with single bilateral bungees as used during normal exercise onboard the ISS. Load cells (Entran, Inc., Fairfield, NJ) were placed in series with the bungee-carabiner system to measure the applied EL during static and dynamic trials at 120 Hz. During static trials, the subjects stood upright during microgravity and EL levels were assessed. One or more static trials were used to ensure that the appropriate EL was applied for a given condition.
Each subject completed locomotion in 1-G on the treadmill while the aircraft was parked in the hangar. Therefore, all trials for each gravity level were completed under identical conditions. Subjects walked or ran for 30 seconds at each speed wearing normal exercise apparel without the harness. Video-based motion capture analysis was used to determine the biomechanics of locomotion. Temporal and joint kinematics at each speed were compared across testing conditions.
Seven subjects completed locomotion trials in 0-G during parabolic flight onboard the NASA DC-9 aircraft. However, during post-processing, motion capture data for three subjects were found to be unusable. Therefore, data from only four subjects were analyzed.
Load cell measures indicate that during static trials, the group mean EL was near the target loads desired for testing with the exception of one subject being underloaded during the light trials. During motion trials, there were slight decreases in EL, as has been reported during prior EL evaluations during parabolic flight. Although not tested statistically, the drop in load during walking and running appears to be greater at low loads than at high loads. There was no effect of gravity level on contact time or stride time at any speed.
The repeated measures of analysis of variance (ANOVA) revealed no differences in range of motion at any segment during each speed between both 0-G load conditions and the 1-G. During walking, thigh angle at the highest EL was greater than during 1-G.
Results suggest that gait kinematics are similar between 0-G and 1-G conditions with the exception of an increase in walking thigh angle at heel strike during high external loading (80% BW) in microgravity. While the thigh angle graphically appears to be very different between conditions, the small sample size may have limited the power to detect a significant difference. Future evaluations would benefit with a larger sample size.
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