Tennis great Andre Agassi knew the value of cross training. A tennis prodigy, Agassi became known more for his fitness than his forehand. He punished opponents with his physical play and made them pay for not being as fit as he was. Agassi predicted a change in the way tennis would be played and prepared for it.

Considered a gentleman's sport, there's nothing gentle about tennis anymore. Powerful shots, grueling rallies and extreme weather require today's tennis players to be physically and mentally strong.

Ericka Saito may not be an Agassi, yet, but she too knows the importance of improving her fitness.

"Running hills helps me stay on my toes," Saito said, "If I stand flat footed (on the court), I know I'm tired and that's not good."

The 14-year-old Punahou student works out every week with private coach Gregg Takata. In addition to developing her hitting technique, Takata works on Saito's fitness by running her through sprint drills, to strengthen her legs; footwork drills, to increase her speed; and exercises to build up her core muscles.

"Everything nowadays is about the abs," Takata said, "If your core is good, your whole body is stronger."

It all sounds excruciating, but Saito said she likes the fitness drills and sees how the drills benefit her game.

"It helps break up the monotony," she said, "After drilling with the medicine ball, the racquet feels lighter, and I get more power in my shots."

Takata recommends these five drills to help you improve your fitness and your tennis game.

1: MEDICINE BALL (CORE MUSCLES)

The drill: This drill requires two people. Sit down as if you were doing sit-ups. Have a partner stand in front of you. Place the ball onto your abs. Each time you go up for a sit up, throw the ball to your partner. When your partner throws the ball back to you, go back down and repeat the drill.

The focus: This works out your core muscles — the muscles of your abdomen and back which support your spine and keep your body stable and balanced.

The boost: Trunk rotation adds power to your shots and that comes from your core. Good balance allows you to hit better shots. You can also reduce back pain by strengthening your core muscles.

You can use any kind of ball to do these drills, but the medicine ball adds weight and will give you a better workout.

2: SPIDERS

The drill: On one half of the tennis court, place five balls where the net intersects each of the lines on the court. Do the same at the service line and the baseline. On the baseline, don't put a ball at the centerline because this will be your starting point. There should be a total of 14 balls placed. From the center of the baseline, run and pick up one ball as quickly as you can and bring it back to the start. Repeat this for each ball without stopping. Once all 14 balls are gathered, without taking a break, put them back one by one. Try to improve your speed each time you do it.

The focus: Not only does this exercise test your fitness and stamina, it also works out your mind. The drill forces you to determine the quickest way to pick up and put back the balls. You must concentrate on the ball, especially when you start getting tired.

The boost: Tennis requires a lot of thinking while moving. When you're tired, bad decisions are made and loss of focus occurs. Spiders build endurance and train you to focus on the ball.

3: HEXAGON

The drill: Take sports tape and make a hexagon with each of the six sides measuring about 1 1/2 feet. Jump into the hexagon, with both feet on one side and then jump out on the next side. Jump in and out of every side, rotating through the hexagon, as quickly as you can. Keeping on your toes will help you move faster. Do this for 30 seconds. Want more of a challenge? Turn that hexagon into an octagon.

The focus: This drill improves footwork and stamina.

The boost: Good footwork and sudden changes of direction are a big part of tennis. The hexagon drill will help you improve your first step and quicken your steps.

4: MEDICINE BALL FOR TRICEPS

The drill: Lift the medicine ball above and behind your head. Keep your elbows shoulder-width apart and slowly move the ball above your head and back down to your back. Do this 10 times. To give yourself more of a workout, toss the ball forward over your head as hard as you can after dropping the ball down your back. You can do this against a wall or with a partner.

The focus: This exercise builds up the triceps which run along the back of the upper arm and are responsible for arm and elbow extension.

The boost: Strengthening your triceps will add power to your overheads, serves and backhands strokes.

You can use any kind of ball to do these drills, but the medicine ball adds weight and will give you a better workout.

5: HILLS

The drill: Find a short steep hill and sprint to the top. Walk down slowly making sure you don't hurt your knees on your way down. Next, run up backward. Do this 10 times each.

The focus: Running up the hill forward strengthens your quadriceps; running backward works the back of the thigh.

The boost: Stronger legs will improve your running, will get more power in your shots and will help you squat to get low to the ball.