Megan Fox's trainer has clients work out for just 20 minutes and walk 12,000 steps a day

• Celeb trainer Harley Pasternak said his celeb clients like Megan Fox and Ariana Grande do 20 minute workouts.
• Using short, intense circuits called supersets helps cut down on hours in the gym.
• Pasternak also has clients focus on walking 12,000 steps a day for fat burning, he told Insider.

You don't have to spend long hours in the gym to build muscle, burn fat, and reach your fitness goals.

Effective workouts can fit into a busy schedule with the right planning and routine, according to Harley Pasternak, a celebrity trainer whose clients include Megan Fox, Ariana Grande, Rihanna, Kim Kardashian, and Halle Berry.

"I'm a big advocate for short intense workouts," Pasternak told Insider as part of a promotional event for his new partnership with the no-sugar dairy company Maple Hill Creamery.

To take advantage of 20-minute gym sessions, aim for little to no rest, plan efficient exercise sets, and do plenty of walking outside of your gym time.

Get the most out of your workout time with supersets

When working with clients, Pasternak likes to combine two movements focusing on different muscle groups in a "superset," moving from one exercise directly to the next without resting. Then, he'll throw in an exercise focusing on smaller muscle groups, like the abs, for every other set.

You can do the movements for a set number of repetitions (20 reps of each exercise, for example) or a set time period (45 seconds to a minute per exercise).

A sample workout, according to Pasternak, would include:

Reverse lunges (to work the quads), followed immediately by dumbbell rows (to build the upper back).

Reverse lunges and dumbbell rows again, followed by pike planks to work the core.

Repeat the entire process two or three more times for a full workout. In total, you'll be done exercising in well under half an hour.

"Workouts are 15 to 20 minutes and then get outta here," Pasternak said.

Get plenty of non-gym activity by walking at least 12,000 steps a day, he said

Maintaining a healthy physique is less about the gym and more about your daily routine. That includes good nutrition and habits like walking, which Pasternak said is the key to fat burning.

"The focus really is on steps, making sure you get at least 12,000 steps a day through walking, moving your body," he said.

For the average person, 12,000 steps a day is the equivalent of walking about five miles.

If that feels out of reach, research suggests you can still see the benefits of walking for overall health by walking 7,000 to 8,000 steps instead.