To estimate to physical force that winding a spring requires, you must take into account the fact that they balance the weight of a garage door applied to a lift drum on either end of a torsion shaft, with the enough torque to keep it in place. Each drum is about four inches across, or about a one foot circumference. (2 x pi x radius) Let’s say that the door, which is likely about ten by seven feet, weighs around three hundred and fifty pounds- the torque is seven hundred inch-pounds. And since each spring exerts a little less than half of this balancing torque, it will be about 350 inch-pounds, or almost 30 foot-pounds. That’s just with bare hands, though. Lets say you use an eighteen inch winding lever for the job, or about 1.5 feet: then you have to apply a tangential force of at least twenty pounds.
You have to respect this amount of force when it is backed up by hundreds of foot-pounds of stored energy that are just waiting to spring into action- holding and turning the handles takes quite a bit of strength. And remember- this calculation depends heavily on the diameter of the drums, how much the door itself weighs, and the number of springs. It may be much less, in the end, or it could be more.
Long story short- if you’re not absolutely certain that you are entirely capable of handling twenty pounds of force for an extended period of time with the danger that hundreds more pounds of energy may fly out and hit you, you probably shouldn’t be trying to do a garage door repair job on your own. Instead, it may be a wiser course of action for you to spring for professional garage door service, and sit back and sip some lemonade instead, letting the professionals handle the potential danger and dirty work.