The Treadmill with Vibration Isolation and Stabilization (TVIS) Harness Comfort Study which was designed as a pilot study was conducted on the Exercise Countermeasures Laboratory's enhanced Zero-g Locomotion Simulator (eZLS) at NASA Glenn Research Center. This experiment falls under the Exercise Countermeasure Project (ECP) and part of the ECP mission is to develop requirements for new exercise equipment designs. This study sought to develop a standardized test protocol for evaluating comfort and effectiveness of two harness designs when loading subjects during simulated zero-gravity treadmill exercise.
The purpose of this pilot study was threefold; 1) to evaluate and compare the comfort of the current U.S. TVIS flight harness design with a prototype harness design (Cleveland
Clinic) using the eZLS, 2) to provide recommendations for improvements to the harness/subject load device (SLD) system which increases comfort and effectiveness for both in-flight exercise systems and ground based zero-gravity exercise simulators, and 3) to identify measurements and data analysis results that correlate with comfort so that future harness/SLD designs can be evaluated with a standardized test protocol. This study was designed as a pilot study to establish a standardized test protocol for evaluating future harness designs. Statistical analyses were done on the data; however the study was not designed with the expectation of having adequate statistical power to make objective conclusions from the data (per NASA JSC Committee for the Protection of Human Subjects - approved protocol).
Six test subjects (three male, three female) were approved for participation in the pilot TVIS Harness Comfort study, under approved Institutional Review Board (IRB) protocol from the NASA JSC Committee for the Protection of Human Subjects (CPHS). Test subjects exercised with a flight replica of the U.S. harness (currently in use on the International Space Station), and a custom-fit prototype harness (the Cleveland Clinic design), at 7 mph for 3-minute sessions on the eZLS at 50%, 75%, and 100% bodyweight (BW), using two subject load devices - the linear motor subject load device (LM-SLD) and flight replica ISS bungees. The LM-SLD applies a more constant force profile during running to the test subject than the bungees, in which the force fluctuates as a function of the amount of extension in the bungees. Subjects also ran for 20 minutes continuously, at 5 mph (slow jog), with each of the two harnesses and the LM-SLD set at 75% BW. Subjects' heart rate was monitored continuously throughout the exercise sessions with a heart monitor (Polar Electro Inc., Lake Success, NY) and wireless transmitter. The maximum allowable heart rate during this study, as dictated by the IRB panel, was 75% of age-predicted maximum, calculated by the formula 220 minus the subject's age in years. Subjective comfort data was obtained from the subjects using the visual analog scale (VAS) comfort rating system at six body locations (shoulders, neck, back, waist, hips, overall). Objective measures included the mean and maximum pressure experienced under the harness shoulder straps, gait parameters obtained from ground reaction force data and the applied External Load (EL) measured with in-line load cells.
The Cleveland Clinic harness was subjectively rated as more comfortable in the shoulders and overall than the U.S. harness. The mean and maximum pressures under the shoulder straps were higher in the U.S harness. There was little difference in gait parameters, regardless of the harness condition. The mean EL applied by the elastomer bungees was less and more variable than the EL supplied by the LM-SLDs. A more comfortable harness may allow for a higher EL to be tolerated and potentially improve the efficacy of the in-flight exercise program on the International Space Station (ISS) treadmill.