I flew the turbo commander with a modified door to allow better access. The pilot stood in the cockpit facing the rear of the cabin. The medic took the foot end of the sled and another medical on the ground passed the head end up to the pilot. The pilot then lifted the sled and maneuvered it onto the med bed inside the aircraft.
9 times out of 10 it wasn't a big deal but every now and again I got an obese patient, and / or a medic who wasn't putting much effort at their end.
I'm in my late 30's and try to stay in shape but I did hurt my back a couple of times. Partly due to me being complacent and not bending my knees. It's more the twisting motion that the lifting.
I guess it depends on the type of system the aircraft uses.
The job itself has its pros and cons like anything else. I got paid to watch breaking bad on my down time but certainly earned my money when the weather was bad and the helicopters wouldn't launch.