Lateral stability during walking requires active control of the center of mass (COM) trajectory. In this short communication, we introduce lead- and trail-limb contributions to mediolateral COM acceleration during gait. These measures expand upon previous center of pressure (COP) contributions by accounting for limb- and phase-specific contributions, capturing the factors underlying previously proposed mechanisms of foot placement, ankle adjustments, and push-off. The COP contribution upon which our proposed measures are based, as well as an accompanying counter-rotation contribution, are quantified from a marker-based approach using motion-capture and force-plate-instrumented treadmill analyses. The purpose of this study was to validate a force-plate-only approach to quantifying lead-limb, trail-limb, and counter-rotation contributions to the lateral COM trajectory. Ten normal-weight, middle- to older-aged participants walked on an instrumented dual-belt treadmill at their preferred speed. Limb- and phase-specific contributions, as well as counter-rotation contributions, were calculated using marker-based and force-plate-only approaches. Agreement between the two approaches was assessed using intraclass correlations and Bland-Altman plots. Estimates for lead- and trail-limb contributions showed moderate to excellent agreement across both marker-based and force-plate-only approaches (ICC(2,1)=0.91 and 0.58, p<0.01, respectively). However, counter-rotation contributions within each phase showed poor between-approach agreement (ICC(2,1)<0.19). The limb- and phase-specific biomechanical influences on the lateral COM trajectory during gait can be measured using a force-plate-only approach in a valid manner.