Increasing the height of your vertical jump means practicing the act of jumping. To add resistance while reducing the stress to your joints as you land, practice jumping in the pool. The water makes you use more force to lift your body, building the muscles you need to propel your body into the air when on land.
To increase the height of your vertical jump, you need powerful leg muscles. Most of your upward force comes from your thighs -- your hamstrings and quadriceps -- with the hip flexors and gluteus helping push you up. The hip flexors engage as you squat to help the quadriceps in the front of your thighs contract, and the gluteus muscles support your hamstrings as you straighten your legs on your way up. You also need strong calf muscles as you leave the ground by pushing off with your toes. Scattered among these muscles are several joints that can be sore after hard landings, but working out in a pool gives you some relief.
Plyometrics uses fast, powerful movements to develop stronger muscles. Using these exercises in a pool means additional resistance, which makes your workout more effective, but it also reduces the impact as you land. According to Ohio State University, performing plyometrics exercises in a pool puts less stress on your muscles and joints, helping you reach your jumping goals with less chance of injury. Squat jumps are an excellent way to increase your vertical jump, but you should pick a water depth that matches your strength and swimming skill. For beginners, head to shallower water, perhaps hip deep, so you don't have as much resistance when you jump and you don't worry about going underwater when you squat. For advanced pool jumpers, water chest deep gives you strong resistance and more cushioning on the landing, but you must hold your breath as you dip under the water's surface. Push your entire body up out of the water to build powerful muscles throughout your legs. Work with a spotter and keep the number of repetitions small, such as five at at time, to avoid getting dizzy if you're putting your head underwater.
While it might feel a little silly to bound around the pool, taking huge steps while you push your body as high as possible, this movement works one leg at a time so that they both have the strength to propel you upward on land. Water that's chest deep is ideal for bounding, and using a flotation belt helps keep you from tipping over as you land. Jump from one foot, specifically your toe to get your calves engaged, and leap as high and as far forward as you can. Landing on the other foot means your muscles must engage quickly to keep you balanced. Push back off from that same foot and land on the other one. Try to bound for one minute to start, and build up to five minutes.
Tuck jumps add an element of speed to your jumping routine. In hip or waist-deep water, bend your knees slightly and push up, bringing your knees high toward your chest. When you straighten your legs to land, be ready to spring back up as soon as your feet land firmly on the floor of the pool. Deeper water offers more resistance. Two sets of 10 tuck jumps is best to start, then you can add more sets or step into deeper water when you're ready for more of a challenge.