Have you ever used TXR straps (short for total-body resistance exercise) in your exercise work outs? You really can feel the burn. They were invented by a former U.S. Navy SEAL. TRX turns every exercise into a challenge for the core by using two very accessible resources: gravity and your own bodyweight. All you have to do is anchor the TRX straps to a secure spot ie a door frame and use either your feet or hands to hold the straps.
Check out this you tube video for some TRX moves.
Let me know if it works for you?