^^ This.

Also, realize that the VMO is only fully contracted at the final ~20 deg. of knee extension. Since it appears that the majority of proper fits have ~30 deg of knee flexion "built in" the seated riding position, that muscle really shouldn't be worked to failure very often, as you have described. Were you standing very often? What type of terrain? Simple thing like seat height, maybe? Saddle fore/aft position? Impossible to know sans pics and/or video. This is all a theoretical opinion, of course....