I’ve come up with a very nice Sprung Floor System that uses neoprene pads as isolation layers between the floor structure components. From what I gathered during my dojo floor research, you don’t want a spongy bouncy floor. Your movement and footing is horrible, and it can cause some pretty bad knee strain working out on a soft floor surface, especially one that moves.
People think they need a ‘soft’ floor to absorb impact, instead, you want a fairly stiff floor, but one that dissipates the impact energy away from the body instead of back in to the body, without being spongy. The ‘softness’ will come from the mats you lay over the sprung floor.
The way I have the neoprene pads arranged (between the floor sheathing and joists, and between joists and joist hangers) you do still get a tiny bit of floor deflection, but the important thing is, the energy is dissipated down and away before it comes back into your body.