Don’t get this wrong. Good planks = really awesome core workout. Planks for so long that your form suffers, not so much. “When you do planks just for the sake of time, it’s at the expense of building any type of useful strength, and actually just reinforces bad habits such as forward head posture, shoulders bunched up in ears, low-back sagging, and collapsed shoulder blades,” says Clifton Harski, director of training and head coach at FitWall.
Try this instead: Harski recommends short, intense “hard-style” planks. To do: Start on your forearms, with your elbows about 1" in front of shoulders—this will require your lats and abs to engage during the plank. With your feet and legs together, begin by squeezing first your glutes, then abs, then thighs, and then—without moving your arms—press your forearms firmly into the floor, while also feeling like you’re pulling your elbows toward your feet. Squeeze everything like hell for 10 seconds. Aim for 3-6 10-second max-effort holds, resting in-between.