The article & vid makes the specific point that this is NOT like walking or running (although skipping was not mentioned). It seems that they are trying to get

The article & vid makes the specific point that this is NOT like walking or running (although skipping was not mentioned). It seems that they are trying to get the muscle to contract while NOT under load. 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...)