When was the last time you did leg extensions?
For me, it has probably been about 10 months. This winter the weightlifting I've been doing (at home, using my own weights) has been focussed on my upper body and core ... I've been walking and riding my trainer to work out my legs.
Yesterday I got a sports center (weights room, swimming pool, track, climbing walls, etc. etc. etc.) membership for a month, and headed into the weights room to check things out. The first machine I decided to try was the leg extension. I chose a fairly light weight and did a very basic 3 sets of 10 reps .. then continued on with a few other things, mainly just checking it all out because I've never been to this facility before. And then I ended it off with 20 minutes on the treadmill. Easy.
Until today! My vastus medialis is killing me!! The rest of my quad muscles are fine ... it's just that one.
This article talks about how important it is for cyclists to develop all their quad muscles ... and my physiotherapists have also told me the same thing.
"Cycling tends to overdevelop the large outer thigh muscle of the
quadriceps group (the vastus lateralis) relative to the smaller
quadriceps muscle to the inside of the knee (the vastus medialis),
resulting in the kneecap being pulled to the outside so it does not
ride in its smooth groove on the end of the femur."
The article also gives some tips on how to do the extension effectively so as to build the muscle without damaging anything else.
If it has been a while, you may just want to consider adding it to your exercise routine once in a while.