So, I'm going to demonstrate how to do a side plank with an arm reach. So, keep in mind that this is a progression from a normal side plank, so if you've never done a side plank, make sure that you start with a normal side plank, and then you can progress to a side plank with an arm reach.
So you're going to go into a side plank position. So you have a couple options here. You can leave your knees on the ground. Your elbow wants to be under your shoulder. Make sure the alignment's always right. Lift your hips, and you're just going to hold this position. When you're ready, you feel stable, you're going to reach your arm under you, and then back up. Under you, and then back up.
If you feel that this is too easy, go ahead and straighten your legs. Keep your legs, keep your feet stacked. Lift yourself up again, making sure your alignment's right, and you're going to reach underneath you and back up. Reach underneath you and back up.
You can also do this on your hands which will just add in a little shoulder, a little more shoulder. So you're just going to get stable, get situated up here. When you're ready, reach underneath you, and then back up. Reach underneath you, and then reach back up. So, stability is definitely more of an issue on that last progression.
But that's how you do a side plank with an arm reach.