This month, skip the countless sit-ups and lengthy plank holds. Instead, let Lauren Williams, the founder of Chisel Club, take you through a 30-day abs challenge that's not only fun to do but also nails each of your abdominal muscles and builds your core's endurance.

Every week, you'll find a quick abs workout that you'll do for four days of the week. On your off-days, you'll do either a HIIT (high-intensity interval training) workout, a sprint, or take a rest. As each week of the 30-day abs challenge progresses, the exercises get a little bit harder (and a minute longer) so that by the end of the month, you'll feel strong enough to tackle all of the exercises in one workout.

On Days 1 and 2 of this 30-day ab challenge, do 30 seconds of each exercise. On Day 3, do three 40-second sets of high knees with 20 seconds of rest in between. For Days 4 and 5, do two 30-second sets of these abs exercises. On Day 6, you'll do six sets of 30-second sprints, with 75 seconds of recovery between each set. Give yourself a rest from the 30-day ab challenge on Day 7.

A. Lie flat on back and lift toes and hands off the floor, reaching away from each other.

B. Sit up while pulling knees into chest and extending arms forward, then lie back again in extension and reset.

A. Lie flat on back and lift legs and hands up toward the ceiling.

B. Keeping core engaged, lift shoulders off of floor and reach hands toward feet, then lower shoulders back to floor.

A. Start in a high plank position with shoulders over wrists, fingers spread apart, feet hip-width apart, and weight resting on balls of feet. Body should form a straight line from shoulders to ankles.

B. Maintaining a flat back and gazing between hands, brace core, lift one foot off the floor, and quickly drive knee to chest.

C. Return foot to start and repeat with the other leg. Quickly alternate driving knees in toward chest as if running.

A. Start in a table-top position on the floor with hands stacked directly under shoulders, knees bent and stacked directly under hips, and feet hip-width apart.

B. Lift both knees off the floor and straighten legs to come into a high plank position on palms, squeezing glutes together and engaging core. Actively push away from the floor and maintain a straight line from head to heels. This is the starting position.

C. Keeping hips square, lower right elbow to the floor, then left elbow, to come into a forearm plank. Place right hand under right shoulder, then left hand under left shoulder to return to a high plank. 

D. Repeat the plank up-down with the left side leading, lowering left elbow to the floor, then right elbow, to come into a forearm plank. Place left hand under left shoulder, then right hand under right shoulder to return to a high plank. 

On Days 8 and 9 of the 30-day ab challenge, do 45 seconds each of dead bugs, leg drops, alternating toe touches, and scissors. Similar to last week's 30-day ab challenge rotation, there's a cardio burst on Day 10, consisting of 40 seconds of HIIT tuck jumps, followed by 20 seconds of rest. On Days 11 and 12, you're back to doing two 45-second sets of these abs moves. It's time for sprints again on Day 13: 30 seconds of all-out sprints with 75 seconds of recovery. Take a breather on Day 14 of the 30-day ab challenge.

A. Lie on back with legs in a table-top position, calves parallel to the floor, arms extended up toward the ceiling.

B. Extend one arm back and the opposite leg down, hovering an inch off the ground, then return and switch sides.

Repeat for 45 seconds, alternating sides.

A. Lie on back with legs extended straight toward the ceiling, hands underneath butt, and core engaged.

B. Keeping legs straight, feet touching, and core engaged, lower legs and stop a few inches above the floor, then raise back to starting position.

A. Lie flat on back on the floor, arms by sides and legs straight.

B. Reach up left arm and right leg to touch fingertips to toes. Lie back down and switch sides.

A. Lie on back, hands under butt for support and legs extended straight on the floor. Lift right leg up to point toward the ceiling.

B. While lowering right leg, raise left leg to point to the ceiling.

Repeat for 45 seconds, alternating legs.

As in the previous weeks of the 30-day ab challenge, Days 15, 16, 18, and 19 are your abs exercise days. (Don't forget to do two sets on Days 18 and 19!) You'll complete one minute of Russian twists, side plank rotations, opposite arm/leg lifts, and banana rolls. Day 17 and Day 20 are your cardio days with HIIT froggers (six rounds, 40 seconds on, 20 seconds off) and sprints (six rounds of 30 seconds on, 75 seconds off). Rest on Day 21 of the 30-day ab challenge.

A. Sit with sacrum on the floor, legs up in tabletop position and back off the floor, hands in prayer. Twist to the right, tapping right elbow to the floor.

B. Twist to the left, tapping left elbow to the floor.

Repeat for 1 minute, alternating sides.

A. Come into a side plank, elbow on the floor below shoulder and feet stacked.

B. Turn downwards into a forearm plank on both elbows.

C. Turn to come back up into a side plank on the opposite side.

Repeat for 1 minute, alternating sides.

A. Start in a high plank position with feet shoulder-width apart.

B. Lift and extend left arm and right leg up, then alternate with the opposite side.

A. Lie on back in a hollow hold, arms overhead and legs extended off the floor.

B. Roll over onto stomach while keeping arms and legs off the floor.

C. Hold in superman pose, then roll back.

The final week of this 30-day ab challenge is a little different (and longer!): You'll do abs exercises on Days 22 and 23 (one set), 25 and 26 (two sets). They include kneeling medicine ball chops, kneeling medicine ball slams, resistance band bicycle presses, resistance band plank jacks, side plank leg lifts, and bicycles.

For the cardio days of the 30-day ab challenge, burpees are added to the mix (yay, Day 24!), followed by your standby sprints on Day 27. On Day 28, you'll get some well-deserved rest. Day 29, you'll repeat the same abs sequence you did at the beginning of the week (one or two sets — your call). Then, on Day 30, you'll do every core exercise in the 30-Day Ab Challenge for 30 seconds.  

A. Start in a tall kneeling position, with knees hip-width apart, glutes engaged, and arms at right hip, holding a medicine ball.

B. Lift the ball across and up over left shoulder.

Repeat for 50 seconds. Switch sides; repeat.

A. Start in tall kneeling position with knees hip-width apart and a medicine ball on the floor on right side of body.

B. Raise the ball up and overhead.

C. Slam the ball down on the opposite side.

Repeat for 50 seconds, alternating sides.

A. Lie on back in a tabletop position and wrap the resistance band around feet. Rest back with hands behind head, elbows out. 

B. Reach left elbow toward right knee, extending left leg out. Press the band to push feet away from you. 

C. Switch sides, driving opposite knee in and rotating shoulders.

Repeat for 50 seconds, alternating sides.

A. Start in a high plank position with hands below shoulders, legs extended, and feet together with a resistance band wrapped around ankles.

B. Jump feet out into a wide stance, then jump feet back together again.

A.Start in a side plank position with right arm straight underneath right shoulder, left hand on top of hip, legs extended out to side, and feet stacked.

B. Lift left leg slowly up and down.

Repeat for 50 seconds. Switch sides; repeat.

A. Lie on back in a tabletop position with hands behind head, elbows out. 

B. Reach left elbow toward right knee, extending left leg out.

C. Switch sides, driving opposite knee in and rotating shoulders.

Repeat for 50 seconds, alternating sides.