I went to the gym the other day later than I normally do and by that time. All the benches were taken up and there were not many free weights left. I decided to do a day of body weight workouts instead so I did push ups, sit ups and planks. I've seen other people doing planks while working out so I decided to try it and see how it went.
To do a basic plank put your forearms and toes on the ground (like a push up position but on your forearms) and then just hold the position. Surprisingly, this will work out your muscles that support your abs. Try to hold it for 20-30 seconds and then rest. Then begin again. Below is a photo of what it should look like.
You can do side planks that strengthen leg muscles to prevent injuries while running by doing the plank from the side by balancing on one forearm instead of two.
Planks are beneficial in strengthening core muscles that help prevent injuries and improve performance in sports and other exercises. The exercises are not too strenuous but if you haven't done them in a while it will feel like you've done a good ab workout. Here is a video about planks and core muscles.