Sit ups; a technique question

[One More Solo]

Ok quickest question ever; when doing sit-ups/crunches is it ok to hook your feet under something (e.g. sofa, bed etc) to help or is that cheating?

 

[One More Solo]

Hmm, the spine problems don't sound very promising...

Mate of mine who is a gym instructor lies on a mat with his feet against a wall, seems to work for him judging by the washboard he has under his shirt.

Flat against the wall? That sounds interesting.