I used Returner to and the object menu and changed allow pregnant sim to true. But my pregnant sim still can not work out. Is there a limitation in place dependent on how far along the sim is? I have pregnancy set at 240 sim hours and my sim is currently 214 hours pregnant.

This is for working out on the treadmill, forgot to mention that.

Some activities are hard-blocked by the game core and take more than tuning changes to open up (if they can be opened up at all). This might be one of them, not sure, but have you saved and reloaded your game since having made the Retuner change?

No I didn't save and reload. I just had her use the weight bench which was allowed. I will see if I can have her use the treadmill after my next reload.