Timing is everything: the effect of measurement timing on trailing limb angle in gait analysis.

Introduction: Progress towards a meaningful clinical measure of propulsion has been achieved through the trailing limb angle, which describes the position of the trailing limb at the time of peak propulsion. However, variations in the timing of the calculation could limit its clinical translation. The purpose of this study was to compare commonly used approaches to trailing limb angle measurement. Methods: Nineteen middle-aged adults (mean age [SD]: 56.42 [4.14]) without impairment completed three-dimensional gait analysis while walking on an instrumented split-belt treadmill. Propulsion was defined as the anterior component of the ground reaction force. Peak trailing limb angle was calculated and compared to the angle measured at the time of peak propulsion. Heel strike and toe-off timing were calculated to describe the time of peak propulsion relative to key gait events. Kinematics of the trailing and leading limb hip, knee, and ankle joints were also calculated. Results: Peak propulsion occurred at 47.50% of the gait cycle, just before contralateral heel strike (49.99%). Peak trailing limb angle (22.77°) was statistically significantly larger than its value when measured at peak propulsion (16.08°, Discussion: Our findings challenge the assumption that peak trailing limb angle is equivalent to the trailing limb angle measured at peak propulsion. Calculation methods should reflect this critical distinction to ensure methodological consistency in both research and clinical settings.