Could R-11 Sound Batt have a large impact on reducing sound
Fiberglass insulation helps more to reduce high frequencies than low. Since the sound made by exercise machines is primarily low frequency (i.e., dull thuds), such as the impact of feet, he insulation would not be very effective.

Some ways to decrease low frequency noise include:


Increase mass of surfaces: Add a layer of board to the floor.
Increase damping: Add a rubbery, elastic, layer, such as a rug or carpet padding.
Seal the edges and openings with elastic padding.