GFCI will not allow things to work
Big AC motors (refrigerators, air conditioners, washing machines, and exercise equipment) can create large current spikes when they start up - especially if they need to fill a capacitor as part of their operation.

A GFCI will detect current going out but not returning. Sounds like the GFCIs are working correctly. This is by design to catch a situation where the user of an appliance become part of the ground path, and why GFCIs can save lives. They work by measuring the current leaving the GFCI device on the hot wire and returning on the neutral wire. If currents do not match within some close tolerance level, the assumption is the current is leaking somewhere; possibly cooking the flesh of a human or pet as it seeks ground. A device such as your treadmill may have a current mismatch that is completely legitimate, but incompatible with a GFCI-protected branch circuit.

You will need to plug your treadmill into an outlet that is not GFCI-protected. If one is not available, I recommend contacting a licensed electrician to assess the situation and possibly install a new circuit for the treadmill in accordance with whatever electrical code is relevant in your location.