To begin the push up exercise, start by placing your hands and feet on the floor with your body supported and your face pointing downward. You can set your feet close together or as far apart as you want for stabilization. You can set your hands together with a close grip or as wide apart as is comfortable, preferably not more than one and a half times the width of your shoulders. If you set either your hands or feet close together, for stabilization the other side (hands or feet) must be set further apart. If you elect to use a more narrow hand spacing you will more heavily work the triceps as well as the front and sides of the shoulder muscles. Remember that when using a narrow hand spacing, your elbows must bend along the side of the body instead of outwardly beside it as in with a wide grip spacing. If you use a hand spacing that is wider you will more directly and heavily work the chest muscles.
While performing the exercise, your body should remain fully straight with absolutely no bending during the movement. A good rule of thumb is to lower your body down to the movement’s lowest point so that the upper arms (the bicep and tricep muscles) will become a little less than parallel with the floor. Hold this position for a split second or more to increase the intensity of the exercise and therefore the work your muscles are performing. After holding your body at this downward position, push your body up to the point where there is a slight bend in your elbows, but not a complete lock out. The reason you do not lock your arms out is that this could cause elbow joint injury as you are allowing the direct force you are exerting through your arms to push your body to be transferred by your elbow joints. Also locking the arms out will take the work and stress away from the chest muscles reducing the effectiveness of the exercise. This is the basic process to performing a perfect push up.
Remember of course that you can also use variation in the way you perform the exercise to increase its intensity and keep the muscles guessing. To do this you may as mentioned above use a closer hand spacing which in addition to more heavily working the triceps and shoulders will emphasize working the inner portion of the chest. You may also elevate your feet by placing them on to a stool which increases the exercise difficulty as you are more heavily working the upper portion of the chest. Performing the push up exercise where you place one hand on the ground and the other on a small step stool about 8 inches high and then switch positions between sets will also give the chest muscles a great workout.
If you have a medical condition you should consult your physician before performing this exercise. Always use caution when performing this of any other exercise especially if it is a movement you are not familiar with.