I got me one of those exercise balls and it helps so much with good sit ups. I feel it from my ribs straight down half past my belly button and it's so much easier on the back. Also good for leg lifts (lowest abdominal muscles) and stretches etc. though I can't say much about the chest. Oh! Lay on your back with a big can of food (if you've no weights like me) and slowly raise and lower your arms, do push ups, and as mentioned pull ups if you're resourceful enough to find a surrogate pull up bar in your home. And always obey the golden rule : Make sure no one is watching! : P