I mean, it's not just leg bouncing in that I can bounce my leg in a way that clearly doesn't activate the soleus in the manner shown in the video. But it also

I mean, it's not just leg bouncing in that I can bounce my leg in a way that clearly doesn't activate the soleus in the manner shown in the video. But it also is just leg bouncing in that there's no more complicated motion than a certain sort of slow, controlled leg-bounce.