Most injuries come from a poorly fitting bike or clothing. Some common pains and potential causes...
Knee pain --- pushing too big a gear, too low a saddle, saddle too far forward, cleats incorrectly fitted to shoes
Hot foot --- cheap shoes, shoes too small, shoes over tightened
Numb nuts --- poor saddle fit, saddle nose too high, saddle too high
Numb hands --- bars too low, saddle too high, poor gloves, stem too short/long
Back pain --- almost anything, but for me stem too short
Sore hips --- saddle too high
Anyone else got some more?