The name XDurance (short for extreme endurance) and the term "Performance Energy" refer to the essential amino acids contained L-leucine, L-isoleucine and L-valine. These are called BCAA's (branched chained amino acids or German branch chain amino acids) and are distributed in many sports to protect against muscle breakdown. Most probably in the weight training / bodybuilding.
I like to drink even a rock star before training, although I honestly notice no difference to other varieties. The BCAAs are dosed very sparingly and go in their effect here something behind the sugar and other stimulants caffeine, guarana, ginseng and acai lost.
Conclusion: Top product when standing on sweet Energy.