1. Opposite Arm + Opposite Leg Taps

Explanation: Lay flat on your back with your legs lifted in the air at 90 degrees and your arms lifted like they are reaching for the ceiling. Then, straighten out one leg while simultaneously straightening the opposite arm out. Then come back to your central position, and do the same thing for the other arm/leg. Focus on keeping your back steady on the ground and your core engaged.

→ Modification: Still laying flat on your back with both your legs in the air at 90 degrees, but keep your arms on the ground at your side. Just focus on keeping your back grounded on the floor, and alternate tapping each foot lightly on the ground and coming back to your central position. Really make sure to keep your core engaged.

→ Challenge: I discovered this from Kira Stokes (follow her on instagram @kirastokesfit); Lay in the same central position as the original version, but hold a bouncy ball in between your arms and legs. Then, when you lower one leg and one arm, your core is not only focusing on that, but also trying to maintain a stable hold on the bouncy ball being supported between now only one leg and the opposite arm.

2. V-ups

Explanation: Lay flat on your back, with your hands resting on the ground but up by your head (not at your side). Then, without using the momentum of your arms, engage your core and lift your upper body while beginning to simultaneously lift your legs. Then, reaching for your toes, tap your feet and then SLOWLY with your core still engaged, lay back down on the mat. It is super important to lift your body using only your core strength so that you are really able to target those abdominal muscles.

→ Modification: Lay flat on your back but with your hands at your sides. Practice just lifting and lowering your legs (keeping them straight) up and down off the mat (ie. leg lifts). This movement will be the foundation of the v-up.

→ Challenge: When you get to the top of the v-up in the original movement (ie. when your hands touch your feet), try to count to 3 before lowering yourself back to the ground. The hold at the top and most unstable part of this movement will really help define your abs.

3. Frog Kicks 

Explanation: Sitting up straight, with your feet slightly bent in front of you, feet touching the floor. Slowly, with your core engaged, rock yourself backwards so that your feet are no longer touching the floor - your back is still straight but you are leaning at an angle, with your bottom on the ground and your legs at a ~90 degrees angle in front of you, toes and arms off the ground. This is also known as a sailboat pose. Then, with your core activated, straighten out your legs away from your body and lower your back as far as you can go (without either ever touching the ground), and then bring yourself back up to your central position.

→ Modification: Set up the same as the central position, but rather than straightening out your legs, from the sailboat position alternate tapping each foot to the ground. Really focus on keeping that core engaged and your upper body stable and relaxed. If that is too hard, then put your hands on the ground to maintain that position and stability.

→ Challenge: Do the same movement as explained above, but you can either add a pause in your "flat" position to really push your core to maintain that stability, or you can hold weights in your hands for an added challenge.