[UConnJulie]

Honestly, I don't know much about ART. I do know a lot about stretching exercises (dynamic and static). They take time. You will make changes in muscle length with stretches, but optimal hold time appears to be about 30 seconds (holding longer doesn't necessarily give you more bang for your buck) with 2-4 repetitions per side. Static stretches should be done daily, but not at a time when you will impact performance, so I like folks to incorporate them at the end of a workout. You can also try adding in some exercises that will dynamically stretch the hip flexors during the workout, like Bulgarian Split Squats, Lunges (in various planes). Then during your rest period, instead of sitting on your butt doing nothing but staring at the stopwatch, do some dynamic stretching or mobility work.

I have found that frequency of stretching impacts muscle length gains significantly, so be sure to do the stretching frequently.