Okay, here from the bible fatdad mentions (
Climbing Ice):
Anyone who has done much front-pointing knows how fatiguing it is in the thighs and calves. Stiff-soled boots with rigid crampons; heels down; dynamic yet relaxed technique; all these will delay fatigue, but there is a much more ingenious solution called pied troisieme that blends the pied a plat with front-pointing footwork. Just front-point with one foot and rest the other by turning it out sideways and relaxing the ankle in pied a plat. When you get tired of front-pointing on one foot, switch over to your other foot. This technique is a far less tiring method of climbing steep ice than front-pointing, and it is certainly easier to learn than pure French technique. It can also relieve the awkwardness of pointing the feet in the opposite directions at the end of a zig or a zag in the pied a plat. Pied troisieme (the name comes from the third position of ballet) means literally "third foot," but think of it as "3 o'clock," the position of the feet when done correctly. For the average climber this technique, used in combination with piolet ancre for the hands, should be the most valuable of all the cramponing methods we have discussed. It works on snow or ice and on all slopes from moderate to extremely steep. You need not be in super condition to do it even on long, arduous climbs.
Note the French naming. I think maybe it's called American technique now because a nationality felt left out.
Maybe Dane can weigh in with more information? Maybe Chouinard "invented" the technique?