The invention relates to a controllable load apparatus for use in machines for resistive exercise training of the human body. The apparatus comprises a pneumatic cylinder (10) having a piston (12) acting on a fluid and a piston rod (14), the piston/cylinder unit (10, 12) being operated on by a person undergoing training. A pressure accumulator (20) is connected to, and pressurizes the piston/cylinder unit (10, 12) at a predetermined pressure during exercise via a pneumatic control circuit (42). Once a predetermined pressure threshold is reached, a valve means operates to prevent further fluid being available for charging the accumulator (20).