Hamstring Curls: The Difference 1/3, If we wanted to optimize how we do hamstring curls, we should be doing either lying or standing, paired with seated; this is because both lying and standing training the knees bend while in hip extension, which essentially double shortens the hamstring, seated hamstring curls are done in hip flexion and trains the hamstrings with length bias. ln a perfect world we would be doing seated hamstring curls paired with either lying or standing to cover both based.