Planks are a classic bodyweight strength training exercise, but they can be detrimental if done incorrectly. Common mistakes include to much arch in the low back and/or the butt too high up. There should be a straight line from your shoulders to your hips to your heels. Engage your abdominals with a posterior pelvic tilt and squeeze your butt cheeks together so you have a tight core the whole time. Your shoulders should be directly over your elbows with your neck and head relaxed for a neutral spine. Don't look up because that will cause too much curvature at the neck and cause pain. Have a friend or family check your alignment as you hold your plank.
If being on your toes and elbows is too challenging or uncomfortable, try putting your knees down and/or going up on your hands. Make sure you maintain the same alignment though with your shoulders and hips, as well as tight abdominals and a tight butt.
Once you master the basic plank, there are many variations to play with. Don't get too fancy though because you still have to maintain a tight core!
One Leg Plank - lift one leg several inches to one foot off the ground and keep your butt tight. This will really engage the quad of the leg that stays on the ground. Hold as long as you can while maintaining tight abdominals and then switch legs.
Plank on Ball - place shins on a ball and push up into a plank. This will really challenge your core and take the pressure off your legs. You might want to have someone hold the ball for you when you first try this to get started. It's no fun when the ball rolls out from underneath you!
Plank on Ball with Shoulder Taps - hold place on ball and reach with hand to tap opposite shoulder. Continue alternating trying to maintain balance on the ball. This is very challenging - keep your abs tight to stay in place. Try not to sway back and forth as your shift your weight from hand to hand.
Plank with Elbows on Ball - place elbows on ball and push up into plank. This can also be progressed to doing roll outs forward and back or side to side with your elbows. Drop down onto your knees if it's too hard to keep the ball under you.
Side Plank - laying on your side, push up onto your elbow and feet. Keep your top shoulder, hip, and feet all in a straight line. Try not to let your hips sag down. Similar to a regular plank, this can be done on your knees or your hands. I prefer my top arm to be straight up, but you can also rest it on your side if that's more comfortable for you.
Side Plank with Leg Lift - in your side plank, lift the top leg keeping your hips in line. Try not to let your hips rock back and keep your body facing sideways. Some people have a tendency of opening their hips up towards the ceiling to compensate, but you want to keep the body vertical to the ground. You want the outside of the hip doing the work (glute medius), not the front of the hip (hip flexors). This is important to build lateral stability. So much of what we do in life is straight forward (including running), but we have to be strong in the side to side plane as well to prevent injury. When performing this exercise, you can lift the leg up and down for several repetitions OR you can simply hold the leg up.
Try to incorporate planks into your strength routine at least two times per week. Do not push though pain if you experience discomfort while doing these exercises. The focus should be on your core without the neck, back, legs, feet or ankles getting aggravated.