Abstract: A leg stabilization apparatus for a trunk extension/flexion test, rehabilitation and exercise machine wherein a person secured to an input assembly of the machine engages in trunk extension/flexion motion. The apparatus comprises a popliteal pad assembly, a thigh-knee pad assembly and a tibia pad assembly. The popliteal pad assembly has two popliteal pads which bear against the back of the person's knees. The height of the popliteal pad assembly is adjustable. The thigh-knee pad assembly has two thigh pads which bear against the person's thighs and two knee pads which bear against the inside of the legs at the knees. The tibia pad assembly has two tibia pads which bear against the tibia. Both the thigh-knee pad assembly and the tibia pad assembly are secured to the popliteal pad assembly by use of telescoping tubes which are locked into receiving tubes in the popliteal pad assembly.