

This 31-day body-weight workout challenge will inspire you to move more, no matter your starting point. Get all the details on the challenge here.
If you want to run longer, jump higher or simply move better, you'll want to make sure you have strong legs and a stable core.
And combining legs and abs into a single workout is an efficient way to build strength in less time, says Morit Summers, CPT, creator of Brooklyn-based training studio Form Fitness and host of our "New Year, Do You" Challenge.
This workout — designed by Summers — strengthens your legs and core without any equipment. All you need is your body weight.
If you're doing the challenge, follow the weekly rep scheme below. If you're doing this workout on your own, increase or decrease the reps and sets based on your fitness level. You should be able to do all the reps with good form, but the last two should feel challenging.
In between sets and exercises, rest for 20 to 40 seconds. You won't feel fully rested (like you were before your workout) but you should feel ready to tackle the next set.
Reps and Sets Per Exercise
Sets | Reverse Lunge | Dolphin Plank | Clamshell | Windshield Wiper | |
---|---|---|---|---|---|
Week 1 | 2 | 8/side | 10 | 15/side | 8/side |
Week 2 | 3 | 10/side | 10 | 15/side | 10/side |
Week 3 | 3 | 10/side | 8 | 20/side | 10/side |
Week 4 | 4 | 12/side | 10 | 20/side | 12/side |
4 Moves to Target Your Legs and Core
The "New Year, Do You" Challenge is accessible to all fitness levels. That's why we're providing a main move and at least one modification or variation.
In the videos below, you'll see one trainer — either Summers or her Form Fitness co-founder Francine Delgado-Lugo — demonstrating the base exercise along with a modification or variation from the other trainer. Choose the version of the exercise that works the best for you.
Move 1: Alternating Reverse Lunge (shown on right)
- As Summers demonstrates on the right, stand with your feet about hip-width apart. Your arms can be at your sides, on your hips or clasped in front of you.
- Step your right leg 3 feet behind you and lower down, bending your knees until they form 90-degree angles. Your right knee should hover an inch above the ground and your left thigh should be parallel to the ground.
- Keep most of your weight in your left leg as you press into your left heel to straighten your left leg and stand.
- Bring your right leg back to the starting position.
- Repeat, stepping back with the left leg. Continue alternating legs.
Modifications and Variations
To modify, don't step backward with each rep. Instead, as shown on the left, stay in the split stance with your feet separated as you lower down and press up, only going as low as is comfortable for you.
Move 2: Dolphin Plank (shown on right)
- Start in a forearm plank, balancing on your forearms and toes and maintaining a straight line from head to hips to heels (shown on right).
- Hinge at your hips as you raise them up toward the ceiling, drawing in your bellybutton to protect your lower back.
- With control, lower back down into a forearm plank and repeat.
Modifications and Variations
You can also perform the dolphin plank from a high plank, balancing on your hands instead of your forearms (shown on the left).
Move 3: Clamshell (shown on left)
- Lie on one side like Delgado-Lugo on the left and stack your legs on top of one another, knees and hips bent at 90 degrees.
- Press your bottom leg into the floor and, with your heels pressed together, squeeze your glutes to raise your top knee toward the ceiling.
- Raise your knee as high as you can without letting your pelvis rock forward or backward.
- Pause, then slowly lower back to the starting position and repeat.
- Do all reps, then switch sides.
Modifications and Variations
To make this move harder, add a hip thrust (shown on the right). As you lift your top knee, press into your bottom forearm and knee and raise your hip several inches off the floor. Lower back down with control.
Move 4: Windshield Wiper (shown on right)
- Following Summers on the right, lie on your back with your knees bent and feet on the ground.
- Your arms can either be straight out to your sides or at about a 45-degree angle from your body with your palms down. Choose whatever arm position feels more comfortable for you.
- Press your lower back into the ground to engage your core muscles. Keep your low back flat to the floor the entire time, not allowing it to arch.
- Bring your feet off the ground and straighten your legs toward the ceiling. This is the starting position.
- Press both of your hands and arms down into the ground to increase your stability as you lower both legs to the left. Lower only as far as is comfortable.
- Brace your abs and use them to bring your legs back to the starting position before lowering your legs to the right side.
- Continue alternating sides. Remember to keep your core muscles tight and engaged throughout the movement.
Modifications and Variations
To modify, bend your knees to 90 degrees with your shins parallel to the floor to perform your windshield wipers (shown on the left). You can also limit your range of motion by only dropping a quarter or half of the way down.