Five workout tips with Angelique Kerber

For CNN last month, two-time Grand Slam champion Angelique Kerber took viewers behind the scenes of her gym workout. The 28-year-old shared some tips and favorite exercises, as well as admitted she wasn't always as in shape as she is now.

"A few years ago I was actually not so fit," she said. “I saw a lot of tennis players getting fitter and fitter so I started going to the gym everyday, sometimes I went twice in the gym."

The hard work began to pay dividends, not only in Melbourne where she beat Serena Williams for her first major, but also in New York last month where she beat Karolina Pliskova in the final.

The keys for Kerber is to have a plan before going into the gym because knowing how long each part of her workout takes helps focus on the one hour she's going to be training intensely. She also surrounds herself with a good team that balance fun and hard work.

Lastly, the German stresses the importance of variety for keeping things fresh.

"When I’m starting, I’m actually enjoying it because it's always something different," she said.

Fitness is a huge part of the game because players need to strengthen everything including their shoulders, legs, core and back in order to both stay fit and healthy.

"For tennis you have too focus on every single part of your body..." Kerber said. "It's important to do everything."

Her five favorite exercises are sit ups for abs, quick-feet footwork for legs, jumping rope for coordination, planks for balance and elastic bands for shoulders.

Kerber had to improve her fitness to keep up with the changing game of tennis into a more powerful sport, spurred on by Williams.

"Serena has shown us that fitness is one of the biggest things in tennis," Kerber said.

Though Williams has 20 more Grand Slam titles than Kerber, the German passed her for the No. 1 spot after winning the US Open, showing hard work certainly pays off.