Exclusive HIIT Workout from Star Trainer Kayla Itsines

If you're on Instagram, you've probably seen Kayla Itsines' insanely toned, tan body on her own page and "re-grammed" as #fitspiration on plenty of others' feeds. And if you haven't, we're psyched to introduce you to the inspiring 23-year-old personal trainer from Adelaide, Australia, who quickly became a bonafide international fitness sensation after she released her first 12-week "Bikini Body Guide" this past January.

Since then, she's amassed 1.6 million (!) Instagram followers, who come to her page for daily fitness inspiration, diet tips, and highly effective HIIT workouts. She's helped millions of women transform their bodies (you have to check out her Instagram page for amazing before and after photos!) through her 12-week program. And lucky for you, we have an exclusive excerpt from the guide, featuring her Week 1 & 3 Arms and Abs circuit. (And click here for a free printable PDF of the workout!)

Directions: Using a timer, perform as many of the four moves in circuit 1 for seven minutes, without rest. Take a 30- to 90-second break between circuits, then perform the four exercises in circuit 2 for seven minutes. Take a 30- to 90-second break. Repeat both circuits one time.

Pushups:

1. Start with both hands on the floor slightly further than shoulder width apart and feet together behind you resting on the balls of your feet.

2. Whilst keeping your back straight and stabilizing through your abdominal muscles, bend your arms and lower your torso to the floor until your arms form a 90-degree angle.

3. Push through your chest and extend your arms to lift your body back into push up position. (And for more pushup variations, see our Pushup Progression Workout!)

Medicine Ball Squat & Press:

1. Holding a medicine ball against your chest (6 to 12 kg), plant both feet on the floor slightly further than shoulder width apart and point feet slightly outward.

2. Looking straight ahead, bend at both the hips and knees, ensuring that your knees point toward your toes.

3. Continue bending your knees until your upper legs are parallel with the floor, ensuring that your back remains between 45 and 90 degrees of your hips. You may choose to extend your arms for balance.

4. Push through your heels, extend your arms and press the med ball above your head as you stand back up.

5. Lower the ball back into your chest and repeat.

Lay Down Pushups:

1. Start by lying flat on your stomach, with arms extended out in front of you and legs straight behind you with your feet slightly apart.

2. Bring your arms in and place your hands on the floor beside your chest.

3. Position your toes in towards the floor and lift your torso onto the balls of your feet.

4. Push through your chest and extend your arms to lift your body back into pushup position.

5. Slowly lower yourself back down so you are lying back on the floor (not a pushup).

6. Extend your arms back out in front of your body and relax your feet. Repeat.

Tricep Dips:

1. Start by placing a bench (or chair) horizontally behind you and sitting on the edge with your knees bent.

2. Position your hands underneath your glutes approximately shoulder width apart on the edge of the bench, ensuring that your fingers are facing forward.

3. Shift your glutes forward off of the bench, and position your feet so that they create a 90-degree angle with your hips. This is your starting position.

4. Lower your body by bending at the elbow until you create a 90-degree angle with your arms. Ensure that your shoulders, elbows, and wrists remain in line with one another at all times.

5. Push up through your heel of your hand and extend your arms to return to starting position. Avoid using your legs to assist you in doing so. Always try and maintain an upright position. Repeat.

6. Make this more difficult by extending your legs completely or placing them on another flat top bench as shown below.

Mountain Climbers:

1. Starting in pushup position with arms slightly wider than shoulder width apart, position your body weight over your hands.

2. Keeping your left foot on the floor, bend your right knee and lift it in towards your chest before extending it.

3. Then place your right foot back on the floor and bend your left leg and lift it in toward your chest.

4. Increase speed so it's as if you are running on your hands. Never allow the leg that is moving to touch the floor.

5. Repeat for as many reps as stated.

Ab Bikes:

1. Start by laying flat on your back with your head raised and hands behind your earlobes.

2. Bend your knees so that they are 90 degrees to your upper legs and your upper legs are 90 degrees to your hips.

3. Extend your right leg so that is approximately 45 degrees from the floor, whilst simultaneously bringing your left knee into your chest.

4. Immediately after you have brought your knee into your chest, extend your left leg completely so that is 45 degrees from the floor and bring your right knee into your chest. This creates a pedaling motion.

5. Once you have grasped the movement, incorporate a twist with the upper body, which can be achieved by meeting the knee with the opposite elbow. For example, as you bring the right knee into the chest, twist your upper body over to the right so that it can meet your left elbow. Repeat.

Sit-ups with Twist:

1. Start by lying flat on the floor with your feet up extended out in front of you.

2. Bend your elbows, keeping your hands behind your earlobes.

3. Engage your abdominal muscles by drawing your belly button in towards your spine. Slowly release your left hand and extend forward slowly allowing your head, shoulder blades and torso to lift off of the floor.

4. As you continue to sit up, twist over your right side reaching past your right foot.

5. Slowly untwist your body and release your torso, bringing your right hand back in towards your ear.

6. Repeat on right hand.

Straight Leg Sit-ups:

1. Start by lying straight on your back on the floor with legs out straight and arms extended above your head.

2. Engage your abdominal muscles by drawing your belly button in towards your spine.

3. Keeping your feet together and heels on the floor, bring your hands towards your feet slowly lifting your head, shoulder blades and torso off of the floor. This will cause your abdominals to contract.

4. Continue to reach forward until you touch your toes (or the action of).

5. Slowly release your arms and torso and return to starting position. Repeat.

For more diet and fitness tips from Kayla, visit her website.