Paul, I am convinced beyond any doubt that the good therapy work (stretching and core) are what helped me to get over this hamstring/butt muscle strain. Fred's point is that you find that overbalance, or overstrength area and you counter it through exercise. I am in agreement with KS' point, but I was going to add that the work you did for the leg on the day AFTER the race is very important. You should have iced the knee right after the race as the first thing, and I would take ibu too.
Fred, a shot put? You can use one of those small weighted plastic balls they have at the gym. I'm guessing they are about 8" in diameter and are meant for exercises of that type. My PT has no use for the prone leg curl machine you see at most gyms. She has me do the following 3 exercise with an activity ball:
Lie on back on floor arms out in T position, ankles over ball.
Do ten bridges, i.e., lift the hips high off the floor.
Now roll the ball to you and away ten times while in the high bridge position.
Now just put your toes on the ball and do ten bridges; a different set of hamstring muscles kicks in.
I actually do this whole thing two times and use 12 as my repeat number. Looks easy, but it really burns the hamstrings. Try it next time you are at the gym.
Today I did 4.1 miles alone. 2.1 slow and 2 easy (9:04 pace). Then I did a whole stretch routine, followed by my core routine. The activity ball exercise described above is part of the core routine. Feeling good. Spareribs