This seems very close to the motion of rapid skipping. Once one can skip without jumping like a kangaroo it becomes almost effortless but also gets a good sweat on.
A key seems to be that the muscle normally is setup to resist a load and so not change length while activated, and also has an unusually high percentage of cells recruited in each activation vs other muscles (most strong contractions in human muscles recruit like 20% of cells, iirc), so this is to get the full contraction effect and not just a resistance effect. (But I'm just reading into it...)