Originally Posted by B. Carfree

First of all, extreme leg fatigue can result from having a low cadence. You may well be straining your muscles (small injuries that get inflamed). Raise your cadence to about 90 rpm or higher. You'll be doing the same amount of work, but with more power strokes to do it and thus lower peak loads. The higher your cadence, the more you are forced to use a clean, efficient pedal technique. If you're bouncing on your saddle, you're doing it wrong.