Stretching what? Why?
i got a very big hamstring inflexibility. and i think that this causes some occasional pain in lower back and knees. how long does it take to reach a good flexibility? i'm doing 4x3 sets for every leg now 5 times a week. is this okay?
Static stretching has a controversial reputation these days. It's questionable if it actually is the best method to correct mobility issues.
I'd recommend you to keep stretching, but also include the following:
- SMR, aka soft-tissue work. Also a bit unresearched method, but many claim it works (Myself included). Take a tennis ball, lacrosse ball, foam roller, a pipe, rolling pin...Pretty much just something you can roll you hamstring into. Go back and forth for 30s-60s or tens of reps. Put object to floor, apply pressure and roll the hamstrings from knee to hip or other way round. You could work on glutes as well, since they also contribute to hip extension. And the bottom of your foot. Rolling the bottom of your foot usually gives you a small increase in hamstring flexibility due to funny physiotherapical things.
- Dynamic stretches and Full-ROM exercises. Get the full range of motion with your hamstrings for short movements. There are several hamstring stretches and exercises. That of course given that your leg is alright with this. Feel free to use as much weight as possible on clean, full range of motion. Dynamic stretches don't obviously need any load.
- Read the article Robert posted on this forum today. It's from Eric Cressey, he knows stuff.