Plank exercises are a simple way of improving the strength of you core by holding yourself up. To perform a plank, lie face down on the ground with your forearms and elbows underneath your chest. Then prop yourself up into a bridged position using your toes and forearms. Keep your body in a straight line and hold for as long as you can (aim for increments of 15 seconds; 30, 45, 60 seconds). It is important that you keep your body in a straight line and not let your hips start to sag. When this happens you can put a lot of stress on your lower back. However don’t over compensate and raise your butt high in the air as this takes the emphasis of the exercise off of the core.
This will help tighten your abs and strengthen your core. Implement 2-3x per week and work hard!