A $30 nordic hamstring curl strap can help you avoid a lifetime of knee pain. A couple years ago, I tried a Nordic curl for the first time and fell on my face. I realized my hamstrings weren't nearly as strong as I thought they were, despite being able to deadlift 500 lbs. I got turned on to @kneeovertoesguy and added every variation of nordic curl I could come up with to my weekly training. I can now do a full nordic curl and haven't experienced knee pain since. The cheapest way to do these is with a NordStick that fits under a doorway and is super cheap. The version I'm using is a lot more expensive, but has a built in back extension. It's called the Shogun Nord-Ex. I think everyone should be doing back extensions and nordic curls.