One of the most ignored joint actions involved in the jump is ankle joint extension. But, this seemingly insignificant action can add inches to your jump. In addition, ankle joint extension in your cutting and running actions will greatly improve your speed and quickness.
To strengthen the muscles involved in ankle joint extension, as displayed in a quick jump, cut, or sprint, do the explosive heel (calf) raise. To execute, heel raises are most easily done on an exercise machine. But they can also be done with free weights while standing on a raised platform or step with a barbell on the shoulders or dumbbells in the hands. You may need assistants to help you maintain balance in this variant.
Inhale and hold your breath as you lower your heels at a moderate rate of speed. As you feel a strong stretch in the Achilles tendon and calf muscle quickly switch directions and rise up as high as possible. In the ending position your heels should be raised maximally and your legs should be straight. Hold the upper most position for a count of two and then repeat.
A key element in this exercise is to exhale and lower your body under control until you feel a strong stretch on the Achilles tendon and calf muscle. At this point you should quickly reverse directions and hold at the top position. In this exercise you create tension in the calf muscles and Achilles tendon in the down phase and then use the energy created in the up phase. This uses muscle/tendon resiliency, a key factor in quickness and jump height.
Doing the exercise with a barbell on the shoulders or dumbbells in hands, requires considerable balance. If you cannot balance yourself well then you should do the exercise on an exercise machine with the resistance pads on your shoulders. Execution is the same. However, every so often do the exercise with free weights to work on your balance as you execute ankle extension. You will not be able to use as much resistance but you will be developing greater balance in the movement.
Be sure that you keep the legs straight when you do this exercise. If you bend the knees you weaken the contraction of the gastrocnemius muscle. Understand that it is a two joint muscle crossing both the ankle and knee joints and thus must be taut at the knee joint when doing the exercise.
It is also important that you do toe raises to strengthen the muscles on the front on the shin to balance development of the calf muscles. Doing this will allow you to develop even more strength of the calf muscles.
For more informtion on this and other exercises specific to jumping, read Explosive Basketball Training. In this book the exercises are explained in detail and are accompanied with illustrative photographs.