ALEX II represents the second generation Advanced Lower Extremity which began with the National Highway Safety Traffic Administration’s (NHTSA) original version (ALEX I, hereafter referred to as ALEX) several years ago. Current efforts have been undertaken in order to make design improvements in the ALEX leg. Many of the aspects of the original ALEX have been maintained, but additional biomechanics specifications for the foot and ankle have since become available and have thus been integrated into the new ALEX II design.

The most significant aspect of the new ALEX II design lies in its flexibility to achieve any desired torque-angle ankle characteristic with relative ease. This means that as future biomechanics data regarding ankle response continues to become available, the ankle can be easily “tuned” to the desired response. This is significant since the ALEX II will not require full redesign should future data provide, or future researchers require, a different ankle response characteristic. This paper emphasizes the flexibility of the ALEX II design in this respect. The importance of the ALEX II design lies in the technique used to achieve ankle moment-angle response, rather than the actual moment-angle characteristic responses achieved, since specifications for the ankle response may well change in the future.