The on-orbit treadmill harness Station Development Test Objective (SDTO) evaluation ran from Increment 21 through 25 aboard the International Space Station (September 2009 through November 2010). A total of six (6) crewmembers participated in the protocol. One (1) crewmember opted out of the protocol voluntarily. Debrief sessions have occurred per nominal procedures. All crewmembers completed questionnaires after select sessions (typically every 3rd or 4th exercise session) which included a modified Borg scale for pain (0-10 scale, 10 being worst imaginable pain) for each harness in specific body areas (neck, shoulders, back, hips, waist, and overall), perceived load ratio (% load at hip vs. % load at shoulders), perceived total load, narrative responses relating to harness fit and comfort, and nine (9) questions relating to harness performance and effectiveness as ranked on a Likert scale (1 to 5, strongly disagree to strongly agree). As a top-level summary, questionnaire responses and crew debriefs confirmed that overall, one (1) crewmembers preferred the ISS Treadmill harness, one (1) crewmember expressed no preference, and four (4) crewmembers preferred the Center for Space Medicine (CSM) harness. Note the Operational Nomenclature designation for the CSM harness was changed to "Glenn Harness." Load data were captured for 3 of 6 crewmembers, issues that arose were troubleshot and fixed. Post-flight inspections of returned Glenn Harnesses (n=3) showed that they held up well to wear and tear. Overall, the Glenn Harness compared favorably in this on-orbit side-by-side comparison as measured by the crew comfort questionnaire and crew debriefs. Specific areas for improvement have been identified, and forward recommendations will be provided to the Human Research Program. The protocol developed for the SDTO provided valuable insight into crew comfort issues, design improvements, and loading preferences for exercise harnessing, and lays the groundwork for better harnessing systems and training protocols.