Strength exercises are very important in developing vertical jump. Many of us cannot achieve good results due to insufficient muscular strength. Such a problem is common among athletes who are relatively fast and whose jump with one leg is good, but whose jump with two legs, from a standstill, without a running start is significantly worse. Such athletes should achieve faster results if they turn attention on developing their strength, not plyometrics. If you have not performed strength exercises regularly before and have weaker legs, you should not do plyometrics before you have increased your muscular strength sufficiently. Strength exercises have also a general positive effect on the health and physical development of their performer. When performing strength exercises you should be careful, because sudden movements may cause traumas and disorders in the cardiovascular system. Certainly you should observe that there is no general tiredness before starting with strength training. Tiredness is a reflex, which avoids overexertion.
When performing exercises, it is also important how much you use the reactive forces and inertia of your body or the equipment, the less you do it, the more muscular tension is needed for performing the movement. Therefore the training is more effective.