Isometric exercises (especially for the core) are underrated and are great for core stabilization and strength.....isometric exercises require you to hold one position (20 seconds for example) without moving.
Planks are top exercises to strengthen your entire core, including your abs (superficial and deep stabilizers) and lower back.....some variations of planks are:
Great article, I have been doing isometrics for a little while now, just when ever I have a spare five minutes I will push my hands together ect doesnt matter where I am. I also bought a device from
www.jym.me which is helping me monitor my progress.