Several staple free weight exercises -- like the chest press, pec fly, French press and pullovers -- are meant to be done while lying on a weight bench. However, if you don't have access to a weight bench, you can substitute a few other pieces of equipment: A stability ball, aerobics step bench or even the bed or the floor can work as a substitute.
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When you lie with your torso across a stability ball instead of a weight bench, your core muscles must work overtime -- so much so that you might want to lift lighter weights until you've mastered this new challenge. You can also ask a friend to help you stabilize the ball at first, or wedge it between two chairs.
Aerobics step benches make an excellent stand-in for weight benches -- as long as you don't mind getting up and down from the lower height. Drape a towel over the bench for makeshift padding.
Bed and Floor
If none of the aforementioned alternatives are available, you can do many weight-training exercises lying face-up on the bed or floor. Both surfaces will stop your elbows as soon as they come even with your shoulders, which can be helpful if you have limited shoulder stability or range of motion. However, stronger and more experienced exercises may be frustrated by this built-in limitation.