How many sets do I need to do with the X3?

With the X3 you only need to do one set to exhaustion! One set with X3 brings a more complete level of fatigue than compared with conventional weights. Comparisons should not be made with the number of sets. The reason multiple sets are used with regular weight is that stimulus is only delivered in the weakest range of motion, when the least amount of muscle is firing. This means very little stimulus, but with X3 all ranges of motion are taken to fatigue.

For a more in depth explanation: