When incorporating planks into your workout, it's important to shoot for time, rather than reps. Kendall suggests you start by holding the move for 30 seconds, eventually working your way up to three sets of 60 seconds.
2. Ab wheel roll out
The ab wheel, admittedly, is a tough piece of equipment to use if you're just starting your fitness journey, but it's certainly effective. In fact, according to Kendall, "Ab Wheel or barbell ab roll-outs are, in my opinion, the most difficult ab exercise out there, but they come with the biggest payoff. This movement capitalizes on the concept of anti-extension; as you roll out, your trunk must work twice as hard to maintain a neutral spine without collapsing under your body weight and gravity. If you're new to this movement, start off on your knees. Once you're more comfortable with it, go up on your toes and try for three sets of 10 reps with minimal rest between sets."