This is the final in the series for basic body weight leg routine, next I will put all these into one routine for easier reference.
With this one, roll back only as far as you feel comfortable.
Do this on a soft surface, like grass, the beach or a yoga mat.
Keep your chin tucked in and your back rounded.
There is a more advanced version where the feet touch the ground behind your head, but that does put strain on the neck, which few people will be trained up for, so I do not recommend it.
Naturally warm up and cool down, this is the most difficult movement of the 5 in the basic leg routine, as you can imagine it also involves a lot of core integration. It actually feels pretty good, so don't be afraid to ease into it when you are ready.
We don't stop moving because we get old, we get old because we stop moving.