Decline pushups are performed by propping your feet against a wall or on top of a bench or chair. The higher your feet are placed, the more severe the decline angle, and the more significant the isolation on specific muscle fibers. Decline pushups incorporate the muscle fibers in the upper portion of the pectoralis major muscle. However, by altering other aspects of the exercise, you can fatigue several other muscle groups.
Isolating the upper chest is the basis of decline pushups. With your hands in a typical pushup position, the fibers in the lower chest are not incorporated because of the angle at which the body will be pushed up. By raising your feet higher, you can move the stress on the muscle further up the pectoralis major. In addition, because of the angle, you will not be able to use your triceps in the movement. In standard pushups, you can use your triceps by keeping your elbows in close to your body. However, on a decline, the angle of your body doesn't allow you to leave the elbows in close without adjusting other aspects of the movement.
You can isolate the shoulders in the movement, taking some pressure off of the chest by moving your hands towards you head. The farther you move your hands up towards your head, the less of your chest you use in the movement. Instead, your shoulders absorb the increased load, and all three heads of the deltoid muscle group are stressed.
Isolating the triceps in decline pushups can be difficult because of the extreme angle of your body during the exercise. By lowering your hands slightly, you allow your shoulders to disengage from the lift, and your triceps absorb the extra stress. You can also place your hands in the shape of a diamond directly beneath your eyes. Both of these hand positions isolate the triceps muscles.
Use caution when performing decline pushups. Any time you eliminate muscle fibers from the movement and isolate a select few, you increase the risk of over training as well as muscle pulls and strains. Never perform decline pushups without a spotter, as your feet can slip or the object that your feet are on can fall out from under you.