I love this straight leg version because my muscular legs don't look good in a true tight skinny white. (amybethcampbell.com)
You can do them as shown, try the single leg version, place your foot in the air or place your feet on a stability ball. (exercisegoals.com)
Once, you are familiar with hanging knee raises, and you can do at least 10 - 15 repetitions, you can start to do the straight leg version. (abmachinesguide.com)