In some of the plane accidents, the pilot had to use all his might to apply the yoke in certain direction to save the plane from imminent crash; in some cases even crew members had to help with the force. So it seems certain degree of physical strength is needed to be a pilot in view of possible emergencies, though it doesn't seem to be explicitly required?
For the Airbus it is not actually require any strength, all the technology is fly by wire, this means that the actual control (Side stick) is not directly connected to any cable, so been this said, there is no actual force to fly any airbus plane. For the Boeing plane, at least for the 737, that's the one I know, when it loses all the hydraulic systems, the aircraft will become on a manual reversion mode and it will need strength from the pilot to move the aircraft controls that are linked to the surfaces by cables, but this is a remote possibility to happen, and if it is the case both pilots can apply force to the control column
Most transport category jets have hydraulic flight controls where the forces the pilot acts on are through bungee spring devices (a pitch feel unit) in the control cable circuit. For certification, pitch feel units normally limit the force required to move the column to full travel to 50 lbs at high speeds and less than that, say around 30lbs, at low speeds (they are intended to simulate the increase/decrease in control resistance with speed that is felt with manual controls). Most pilots, even small framed males and females, can pull 50 lbs, although sustaining that for more than a few seconds can be a problem. But, there's someone beside to help.
This question really is way too generic to be easy to universally answer.
The amount of force required to operate the controls of different aircraft under identical conditions is different, varying from very little to requiring some serious muscle.
Now apply that to a wide range of potential emergency scenarios. At the one end we have emergencies where no amount of force will change the outcome either because the relevant controls are no longer there (ripped off vertical stab anyone?) or because their use is irrelevant to the emergency (landing gear not extending on approach for example). On the other end we have emergencies where the controls are jammed but can be moved manually if only enough force is applied to them (e.g. the hydraulics failed, leaving the controls stuck in a high deflection position but they can still be moved if you are strong enough). THAT would require a serious amount of muscle most likely.
But it all depends on the aircraft, the emergency in question, and the flight regime in which the aircraft finds itself when considering whether any amount of input at all will save the day, let alone brute force.
It would be very helpful to narrow this question down as to whether or not "physical strength" is needed due to a failure of a built in mechanical/hydraulic system (like losing power steering in your car), or simply in a cable driven control surface system, found in recreational aircraft.
Enormous physical strength is NOT required to be a pilot, although good mental and physical condition is a must. Endurance of concentration and stamina of strength do help as you may be required to "go around" after a long flight.
More strength is needed at higher speeds due to aerodynamic forces, but that is part of Vne. Please do not imagine three people tugging at the controls to save a Piper Cub.
So, depending on your abilities, careful research and expert instruction will get you going in a plane that suits you.