Planks can be done wherever you are with zero equipment. What's more is that you can vary your planks and mix things up.
Ellie suggests "a forearm plank, side plank, plank with shoulder taps (right hand taps left shoulder, left hand taps right shoulder), mountain climbers (right knee tucks to right elbow, left knee tucks to left elbow), and plank leg lifts (lift right leg, then lift left leg)."
If you're watching TV, Ellie reminded us that "a one-hour TV show has an average of five commercial breaks, which are up to four minutes in length." Her tip? "Pick a different type of plank to do for the duration of each commercial break." Netflix and chi . . . seled abs.
Muscles targeted: shoulders, triceps, chest, core, and glutes