Eccentric motion exercises seem to alway stress the negative in any lift. I had been doing these glute exercises with an explosive flex and and a passive extension, not resisting the negative, which is fine, but it was doing nothing for my hip flexors or hip stabilizing muscle groups. Videos show (1, 2) assisted flexing and resisted extending eccentric exercises. I think they can be combined by doing an explosive glute flex and fighting the negative back from hip extension and also the opposite; hip flexing (knee up) fast, slow resistance to extension. The resistance seems particularly effective for the hip flexor when the leg reaches straight - toward extension.
Anyway, when doing the same weight on glutes on the glute/hip machine that I used to do 50-60 times (320lbs), I do half as many reps and fight the negative very slowly with good form. Doing this I can feel all sorts of other muscle groups firing, including stabilizing muscles on the leg/hip I'm standing on (not moving). I still get a decent glute burn and it makes the hip flexors feel great. Did the same thing with the hip flexion exercise. With the hip flexion exercises, I could do 240 lbs on the injured side, strong, no pain... just 40 lbs less than the non injured side.
I talked with Johnny about this and he says these injuries are more likely due to a lack of flexibility and sprint form issues than a muscle imbalance. The glutes will always be stronger than the hip flexors. Still think the tight thigh wrap during the race may have contributed to my lack of flexibility and to the injury.
The workout left my hip flexor injury feeling strong, much better. This should get me back soon, too bad I can't get to this machine more than once or twice a week. I'll continue with bands. This is exactly what I need.
I think I'll hit the track Mon, Wed, and Sat this week. Looks like really nice and cool weather.
2 x 25 glute flexors w/ 320 lbs
3 x 15 hip flexors w/ 280 lbs R, 240 lbs L
1 x 15 w/ 130 lbs adductors and abductors