By Tanner Garrity Planks suck and this one is the worst. The Copenhagen plank is a variation on the toughest part of your mat Pilates class: the already notorious side plank. This version specifically targets the adductor muscles (a group of five muscles in the inner thigh). We tend to neglect these muscles when working out — the fact that they’re always covered with clothing might have something to do with it — but they play a crucial role in hip mobility, injury prevention and core strength. You’ve likely seen people in the gym or on Instagram working their abductors, which are located on th…