Tripping is a common cause of falls across different age populations particularly in older adults. Concerns regarding the validity of simulated-fall research protocols reside in the current literature. The purpose of this study was to develop a novel treadmill-based tripping protocol that allowed researchers to deliver unanticipated tripping perturbations during walking with a high level of timing precision. The protocol utilized a side-by-side split-belt treadmill instrumented with force platforms. Treadmill belt acceleration profiles (two levels of perturbation severity: small perturbation vs large perturbation) were delivered unilaterally when the tripped leg bore 20% of the body weight during early stance. Peak trunk flexion angle during trip recovery was the primary variable used to represent the fall recovery response and likelihood of falls. Test-retest reliability of the fall responses was examined in a group of 10 young participants; validity was examined through differentiation of the fall responses between young and older adults (age 20.9 vs. 57.1 years, n=10 per group). We found that the perturbations were precisely delivered during the early stance phase (10-45 ms after initial contact). Moreover, this protocol elicited excellent reliability of recovery responses during both perturbation severities (ICC=0.944 and 0.911). Older adults exhibited significantly greater peak trunk flexion angle than young adults (p=0.035), indicating the current protocol was valid in differentiating individuals with different levels of fall risks. This novel protocol addressed some of the issues of previous simulated-fall protocols and may be useful as a tool for future fall research and clinical intervention
