The support arm has a shaft (7A,B) with hand grips and an anterior boom (11) connected to the shaft and having fixings (14,5) for the handle of the power tool and connections for the tool controls to the shaft hand grips. The shaft can be formed of two sections (7A,B) which slide with respect to each other. The end of the shaft is connected to the anterior boom by an articulation with positional stops.
