To note, if you look at my ribs (directly below my chest), the second I bring my hands and band forward, I intentionally tuck my ribs towards the front of my pelvis and brace my core big-time. This will help activate the muscles in my anterior core.
Please note, doing this exercise without tucking the ribs and bracing the core renders it (and most other exercises) pretty ineffective. What I like to look for, quite often, if your shirt wrinkles, it means that you have tucked your ribs, whereas if it flattens out, they have flared.
1) Grab onto the band. Clasp hands together and intertwine fingers, versus putting one hand on top of the other, as doing so will make your body uneven in alignment. Picky maybe, but every minute detail matters!!
2) Bring your arms forward so your hands are at least to the level of your chest, if not lower. Doing so will automatically help your ribs tuck, which will help you engage your anterior core.
3) Keep your body in this position, and keep your legs relaxed. Now slowly extend one leg. Bring that leg back to the starting position, and repeat with the other leg. Many people have the tendency of tensing up their legs so they end up using their legs instead of their anterior core. If you find that you are feeling your hip flexors or quads, make sure that your ribs are tucked and legs are relaxed. You can also make this exercise easier by shortening up the lever length of your leg, and bending your knee to 90° and keeping it in that position. The more extended your leg is, the more challenging the exercise will be.
4) Make sure that you are not allowing your back to arch and lift off of the floor, but don't flatten your back. Keep the natural curve in your back, and if you are engaging your anterior core, this should be accomplished automatically.
5) Don't hold your breath. Keep breathing, and brace your anterior core big-time.
6) As your strength increases, you can increase the intensity of this exercise by using a thicker band.
As I've talked about on countless occasions, having a strong core matters, in terms of your overall performance, AND also keeping you healthy and injury-free. This exercise (and exercises that have a similar philosophy) will have a massive carryover effect to all exercises and activities that require you to use your core, which is pretty much everything. Don't let your core be your weak link.