Did he say your muscles become temporarily unloaded if you stop mid rep? lol
If that's the case, you'd could just hold the position all day.
You have a lot of running gurus who talk shit like this as well, yet, they never seem to produce any top of the food chain runners.
There's a YouTube of a supposed biomechanics expert who claimed Shalane Flanagan, the best female Marathoner in the country, was inefficient because her right leg stride length was longer than her left, and that she could be faster if she increased the length of her left side stride.
The problem with his argument is that it assumes that we have exactly equal strength on both sides of our bodies.