[dos]

Your hamstrings are both knee flexors and hip extensors. If you are doing RDL's or good mornings you really should feel significant hamstring activation. You are probably used to the localized discomfort you might get from the knee flexion movements such as leg curls or even the discomfort that you get in the quads from doing leg extensions. Believe me (as most everyone who has done them on this board will attest...) if you have ever done a few sets of well executed gm's or RDL's, you will surely feel them (especially the next day).

In general, open chain movements such as leg extensions / curls bring little to the table in terms of functional strength due to the lack of co-activation of the antagonist muscle....this is how the hamstrings / quads work in real life hence the 'worthless' label. Many will argue (Alwyn comes to mind) that doing these types of open-chain movements to 'isolate' these musclce groups will actually make you WEAKER when performing functional movements such as jumping, sprinting etc. as your body will not even know how to use this 'new found strength' in the real world.