This is the biigest difference between Boflex and other weight training equipment and free weights:
1. Boflex uses a user defined motion path, more similiar to cables then dumbells. BUT ALL user defined motion path exercises works best with the force of resistence IN LINE with gravity, and in the case of cables and Boflex, first in the line of cable resistance and 2nd to the line of gravity. If the resistance is NOT in line with gravity, the user defeind path of motion would feel very awkward and unstable.
2. All other machines operate on the machine defined path, how many planes of motion varies from machine to machine. Machine defines paths requires less stabilization thus gives you increased isolation.
3. The resistence on the Boflex increases as you go through the movement, this is because the resistance is generated through bending of the blades.
4. Free weights and even machine defined exercises depend on a constant resistance source: A weighted plate. BUT, the actual amount of resistance generated by a motion is LARGELY dependent on the torque generated by the angle of the motion AND also the camber shape and mechanism of the machine. THEREFORE, the designer of the machine can selectively choose the point of the greatest resistance in the path of the motion. It can be at the begining of the motion, middle, the end, etc, etc.
5. All joints tend to be the strongest at the mid portion of the motion and the begining the weakest. This is becasue the microscopic contractile units of the muscle fiber just does not work very well when it is at its shorted and longest states. Furthermore, at the beginning of the movement when the muscel is at its longest state, it loads very poorly and a lot of the load is transfered to the tendon, ligaments, and joint capsules, which are not contractile tissues and can get injured from too much loading.
Boflex is a rather safe equipment because it places the least amount of resistance at the begining of the motion (or when the muscle is at its longest state.) However, this is not all that natrual as it does not coincide with the normal strength curve of the muscle, meaning not giving it enough resistance when the muscle fiber is natrually at its strongest position to take advantage of resistive traiing... So you will get great results, but just not like a real gym...