Jazloc, what BSRU is getting at is this: if you tend to use small gears and pedal slowly you will be over-stressing your joints, which can cause stiffness. The accepted wisdom is that you should try to spin faster, which means using a bigger gear at the back and lighter loads on the legs. It's like the difference between driving your car up a hill in third gear and allowing the engine to rev a bit with a light load or flogging it up in fifth at low revs, stressing the crankshaft bearings.
Oh, and the easy simple way to measure cadence is to count the number of revolutions of one foot per minute, as BSRU wrote later in his post.
Saddle height is important too and the best way to get it right is to sit naturally on the bike with one pedal at the bottom of its stroke. With your heel just touching the pedal your leg should be hanging in what is called the "naturally cocked" position, i.e. slightly bent as it will hang if you just allow it to hang freely without straightening it. While pedalling the flexibility of your foot and calf takes up the slack. Don't let any muppet tell you that you ought to be able to touch the floor, that's the wrong advice.
