The recessed lights in the work out room flicker when my wife walks on her tread mill. When she stops walking but the machine is still running the flickering stops. The light flicker is minimal

Your work-outroom is missed wired.

The lighting and receptacles are most likely on the same circuit.

When the motor on the treadmill kicks in the combined amperage draw cuses the lights to flicker.

The only fix for this is to place the receptacles on a separate circuit.

I suggest that you either run a dedicated 20 amp circuit for the treadmill or redo the branch circuit to separate the lights from the receptacles.

Have her walk and stomp about the room with the machine off. Do you get any flicker? Seems like the flicker is more associated with her movement rather than the machine running from what you say.

Nestly,
Yes I would like to see if the flicker is caused by the motor load from treadmill on the same circuit as the lights... troubleshooting or experimenting can be fun!
1) Try "stomping" around...
2) run the treadmill at a somewhat slow speed and try to apply a significant load to the motor, that is try to slow down the belt...

Either way I agree that separating the circuits would likely cure the flicker.

I am experiencing the same thing. It is happening independent of the stomping. The tread mill needs to be running. We have our chirtmas tree in the front room dimming on and off with the beat of the running as well as hall lights and others on one side of the house. The rest of the house (kitchen and family room) are not affected.

@mattgranz. It's probably nothing to worry about; the treadmill and Christmas lights are on the same circuit, and the motor is causing the lights to flicker. If you're not tripping breakers or blowing fuses I wouldn't worry. If you have a fuse box rather than a breaker panel, just make sure there isn't too large a fuse being used.
If it is annoying, you could try plugging the treadmill or Christmas lights into an outlet on a different circuit.