I do it before the children get up, on my exercise show on Lifetime or Denise Austine treadmill, or outdoors for a fast walk. Great way to lose weight and firm muscles, try doing it 3 days a week for 20-30 minutes to burn fat and work on cardio system, which will fight heart disease and obesity. Yes, firm the muscles underlying the breasts to help lift the chest. Great one, lie on back, arms lifted out sides and press chest arms together, do this everyday for 2 minutes, slowly. Eventually add 5 lbs weight.
Pushups are also very good.
Exercise is the fastest way to speed up metabolism. Eat about 1800 calories a day. It could be both - make sure knees are bent to protect back, and the slower the situp the better. Try my fitness video Hit the Spot Abs Vidio to do it correctly. I act as personal trainer.