A great way to improve performance in volleyball athletes would be to train in various planes of movement.
Many of us in the gym only train in the Sagittal plane, leading us to only know how to move forward and backward. Volleyball is a sport where you need to move in three dimensions, so one of the best ways to increase your performance would be to introduce two other planes of movement into your workouts.
Frontal plane workouts include side-to-side movements, also known as lateral movements.
Exercises such as Side Lunges and Lateral Band Sprints would be examples in this plane of movement. These exercises would be perfect for defensive play, to increase your power and coordination in order to chase after the balls that are out of reach in a volleyball game situation.
Transverse plane workouts include rotational movements.
Exercises such as TRX Rip Trainer Wood Chopper and Russian Twists are great examples. This plane of movement is most over-looked, yet it is one of the most important. When we hit a volleyball, we require a rotation in your body in order to produce power in the arm swing. Training rotational power transfers to stronger attacks to help get the big points (and be a great crowd pleaser).
As mentioned already, Sagittal plane workouts include forward and backward movements.
Exercises such as the Back Squat and Deadlift are prime examples of what many people do in the gym. These exercises help improve over all strength and create a stable base for the body. As you progress with Back Squats and Deadlifts, you can increase strength and power that will lead you to increase your vertical jump. Jumping is a huge aspect in volleyball, both in offensive and defensive play, to either create and attack or to block an opponent's attack.
We live in a three dimensional world. When done properly, these exercises not only increases performance in volleyball, but will help reduce injuries in everyday life.