Activity and gait phase recognition algorithms are used in powered motion assistive devices to inform control of motorized parts. This thesis includes the development and evaluation of two independent recognition algorithms for walking, stair ascent, and stair descent activities. The first algorithm detected foot-contact and foot-off gait events within these activities and detected these events within 0.04s of a force plate. The second algorithm was machine learning-based and was developed using inertial measurement data from 80 participants. It simultaneously detected activity and gait phase with 91.2% accuracy and 22.9% of perfectly classified strides. Results from this thesis support the use of FSRs for data labelling for machine learning-based recognition models, the use of machine learning to detect activity and gait phase for walking, stair ascent, and stair descent, as well as the use of proportion of perfectly classified strides as a metric to evaluate activity and gait phase recognition algorithms.