Planks, an extremely effective isometric exercise, are great because they use your own bodyweight to maintain the stability of your entire core, which is exactly what the core muscles are supposed to do, and prevent back pain. Personal trainers always recommend this resistance exercise. The key is to master the basic plank as it’s one of the best moves for strengthening your core. The possibilities to vary a plank are endless; just use your imagination. All of them target the muscles in your back (erector spinae)and abdominals (rectus abdominis, transversus abdominus). Secondary muscles in your shoulders, chest, quads and glutes are also engaged depending on what kinds of planks you’re doing. Most of the variations on this list don’t require any equipment.