Planks are an effective way to work your abdominals as well as your lower back, shoulders, glutes and chest. A straight arm plank creates more of a challenge since it offers less stability than the forearm plank.
They look pretty easy, but if you have bad form, they can end up hurting your back and shoulders.
Here are the things to watch for while doing a plank:
To do a proper straight arm plank, come to the top of a push-up position and align your wrists straight below your shoulders. Keep your feet about hips' width apart and keep your heels high. Avoid an arch in your lower back by pulling your abs in and lifting your ribcage and hips. Lastly, be sure your ears are aligned over your shoulders.
Once you have proper form like below, hold the position for 30 seconds, or as long as you can, and don't forget to breathe!
For an added challenge, try these variations:
Straight arm plank with leg lift - while keeping your proper form, raise one leg in a slow, small movement and lower back down. Lift for 10 reps and switch to the other leg.
Bent knee plank - while keeping your form, bend one knee and lift, making small movements. Complete 10 reps and switch to the other leg.
One arm & one leg plank - while keeping your proper form, lift your right leg and left arm simultaneously and hold for 5 - 10 seconds. Lower and switch to the other arm and leg. Alternate for 20 reps.