Thrusts #1 and #4 are Accelerating (and mutually exclusive) Thrusts. Thrusts #2 and #3 are Non-Accelerating.
The question I answered required differentiation between the use of the Right Triceps in Thrust #1 (Muscle Power) and #2 (Extensor Action). And that essential difference is in Accelerating (the Left Arm moves) versus Non-Accelerating (the Left Arm is stretched but does not move). Hence the need for my broader classification of the four Thrusts into their respective categories.