I agree with Sue.
A long time ago straight leg sit ups were the go to exercise for abs.
Next thing you know, straight leg sit ups were bad for the back and crunches were ‘the’ abdominal exercise.
Now Jeff’s view holds up: ‘there are no bad exercises but there are bad exercises for some people’.
Straight leg sit ups require perfect form. People will experience pain if:
a) they round the back
b) they put their head down
c) they perform this exercise and have not done any abdominal exercises
in a long time
I do not use this with most people because they tend to have bad form.