The essentials

A dense mat under cardio equipment is not optional in an apartment. It cuts structure-borne vibration, which is what travels through a slab and reaches the flat below far more than airborne noise does.

All picks Cardio Strength Small space Recovery

Good to know

Does a mat actually reduce noise for the flat below?

It reduces the vibration transmitted into the slab, which is the part neighbours hear. It does little for airborne sound, so it helps but does not silence.