If bending forward with straight legs causes pain below one sitting bone, you may have injured your hamstring tendon.
I left not for physical reasons - I'd had a torn hamstring tendon in 2003, but it hadn't affected my speed - but because it was my season for change.
Conclusion:ACL reconstruction by knot-impinged double-strand hamstring tendon has satisfactory biomechanical properties in vitro and is an available method to repair the injury of ACL.