Most athletes include Sissy squats, of similar forms of quad stretching, in training. It can be a lesson in pain at first when learning to do them the right way (book, video or from someone who has had experience doing them). Worth the effort after awhile. Can be a question of balance for some, so it needing support use it. Don't need any weight, but try doing them slowly, working towards a full stretch each rep. You want burn......here it is.
Hanging sit-up's have been around a very long time. Simple exercise with great results, because it hit's the low and upper ab's in the same movement. Also the lower back & hams. Inverted boots are being used in the video but most guys will use the hock behind the knees to lock into that upside down position....which can affect the hams even more because the hams are in a semi contracted state. It's just a basic schoolyard or public park movement you can see most everywhere. Guys with bad backs, who use inverted boards, will also do reverse situps. Ab hangs (slang) can be used in a PR or Smith Machine also....probably easier for a lot of folks.
Seen a couple of gymnast do reverse sit-up with the legs wrapped around a climbing rope. Which reminds me: rope climbing is an excellent upper body exercise, including the forearms and biceps. Of course, also improving the grip along the way. Doing them with the legs held at a 90 degree angle...more the better. Chins are a good combo with rope climbs....potential exceptional back developments.
Good Luck.
