I have to post a reply to this one as it's near and dear to my heart.

There was a study done on 100 olympic level cyclists to show which muscles were used where in a pedal stroke, these are the results: This study was done by the Nautilus Institute.

If you look at your pedal stroke as a clock, between 12 and 3 is where all muscles used are engaged at the same time, these being - Rectus Femoris, Vastii, Gluteus Maximus, Soleus, Gastrocnemius and Hamstrings. This is the power phase of your pedal stroke.

After 6pm most of the work comes from use in your Gastrocnemius, not your Hamstrings, your Hams shut off at about 6:35pm!

Your Hams, Glutes and Neck/Traps get very tight and shortened through cycling, so your Hams would be the #1 thing to stretch after a ride. They need work to help keep them as strong as your quads, leg extensions and squats are good exercises that that help with strength and flexibility.

Hope this helps a little as there is much confusion about such things in the world of cycling today.

Wizzer