An outrigger assembly for support of a mobile crane or excavator upon the ground, includes a plurality of outriggers mounted to a vehicle frame and having free ends, wherein each of the outriggers has a ground-engaging pad connected to the free ends for vertical movement in relation to the ground. Each of the outriggers has at least one outrigger arm unit movable with respect to the vehicle frame between an idle position suitable for travel between sites, and an operative position suitable for support on the ground, wherein the outrigger arm unit includes an outrigger arm made of a hollow profile which has a lower part of U-shaped configuration and an upper part of calotte-shaped configuration.