A walk power mower has a traction drive system that includes a front transmission powering a pair of front wheels and a rear transmission powering a pair of rear wheels. A first one of the transmissions provides forward motion of the mower when it is active and a second one of the transmissions provides rearward motion of the mower when it is active. A slidable handle grip on the handle having a cross bar long enough to be gripped by both hands of the user activates the first one of the transmission when it is slid downwardly on a handle out of a neutral position thereof. The slidable handle grip activates the second one of the transmissions when it is slid upwardly on the handle out of the neutral position.