According to Amy Rosoff Davis, variation is key when it comes to workouts. 

When it comes to whipping A-listers into tip-top shape, Amy Rosoff Davis knows a thing or two (she trains Selena Gomez, after all). But whether you’re a celeb client or someone a little less famous, her training principles remain the same: balance and wellness. “I’m not about making the workout crazy and obsessive, but doing things that feel fun,” says Davis.

For Davis, it’s all about encouraging her clients to find ways to move that they love—and that means giving them a variety of different workouts (she calls them “kitchen-sink workouts,” FYI). “I will do kickboxing with someone one day. I’ll do an entire yoga flow another day—sometimes it’s a really hard yoga and others it will be Ashtanga, which is more of a detoxing type of yoga. I’ll make them do two minutes of jump rope on and off for an hour,” she notes. “I get bored doing the same stuff and I know Selena and my other clients would be bored doing the same thing every day too.”

It's this focus on variation that not only keeps her clients interested, but also helps them reach their fitness goals easier and quicker. “A lot of people don’t know that you need to do some sort of cardio and some sort of toning to get results,” she says. “To build musculature and get your metabolism working, you have to do some of those toning moves. But cardio you need for your endurance and stamina and to burn calories.”

So what are some of the specific go-to exercises Davis shares with her clients (and Selena, specifically)? Check out Davis’s four favorite moves below—all of which focus on core strength, while still toning your arms and butt. Each move engages all your muscles and works them in different ways. “I find it really helps get results and makes people strong,” says Davis.

1. Inchworm to Push-up to Shoulder Taps

Stand with feet a little wider than hip-width apart. Hinge forward at your hips, bending your knees, if you have to, and place your palms on the ground. Walk your hands forward to come into a high plank. Bend elbows and lower chest down to the ground. Push back up to high-plank, and while keeping hips square, lift the right hand off the ground and tap the left shoulder. Place the right hand down and then repeat the move with the left hand and right shoulder. Do 5 taps and then walk hands back in to feet and rise to standing. This is one rep. Repeat entire sequence 5-10 times.

2. Second Position Plies w/ First to Second Arms

Stand with feet a little wider than hip-width apart and toes pointed out at 45 degrees. With a one-pound dumbbell in each hand, hold arms at sides so that they form 90-degree angles; palms should face forward. Bend your knees and lower your hips down until your thighs are parallel to the floor. This is your starting position. Pulse up and down while alternating between extending arms straight out as you rotate them so palms face back and returning them to starting position. Start with 30 reps, making your way up to 50.

3. Double Mat Roll

Lie faceup on a mat with legs together and arms extended straight overhead. Roll over to the left, completing one full revolution. When you reach face-up again, bend knees and place feet firmly on the ground as you sit up, raising torso toward knees and lifting arms up. Slowly reverse motion back to start and then roll to the right and repeat. This is one rep. Do 10.

4. Hip Up + Leg Lift

Sit on your left hip with legs stacked; bend legs so feet are behind you. Place left hand on ground for support and right hand on right hip. This is your starting position. Lift hips, coming onto left knee as you lift right leg up and extend it straight out on a diagonal. Keeping hips up, bring right leg back until knees meet. Then, with leg bent, slowly raise your knee up, until it is parallel to the ground. Lower knee back down, and then drop hips back down to the ground. This is one rep. Do 30, working your way up to 50.