A resistance exercise machine has a frame that includes a base on the floor and upright posts on the base. Resistance packs mounted for adjustment up and down on the posts are equipped with cams that compensate for the increased resistance resulting from increasing deformation of the resistance elements in the packs. The resistance packs are interconnected by teeth on their rims which allow the packs to be arranged in a stack. An adjustable bench and seat are provided. One alternative is a direct drive system having angularly adjustable levers. Another alternative has a fixed number of resistance packs that can be selectively activated to add resistance.