If you've had to manually open your garage door recently, you might want to think about getting a garage door opener! Or, if the garage door seems more heavy than you're used to, don't worry- you're not out of shape. Odds are, if you have an old enough door that you don't have an opener, it's likely that you garage door isn't doing its part to lift smoothly and easily. The several hundred pounds of a garage door requires some mechanical help from the springs. If you don't have that, there's no way you're getting that door open.
In general, rolling doors use counterbalance springs that basically use tension to balance out the weight of the door. Normally they're in a torsion arrangement over the top of the door, one on each side along the ceiling next to the door track. The rustier all of these parts are, the more worn-out, the harder the door gets to manually lift.
You can lighten up the load by switching out springs, it's true. It's less expensive than getting a whole new door, and can be done relatively efficiently by garage door service companies.
But for the ultimate in comfort and convenience, it's probably time to get a garage door opener.