The plank march is a variation of the plank that adds anti-rotational elements of trunk and hip stability.
From a plank position, lift and reach one arm and the opposite leg. Attempt to not allow the rest of the body to move. Replace and switch.
The plank march adds difficulty by creating instability and forcing the trunk and hips to resist rotation and changing forces.
The plank march can be done at the end of training sessions for 3-5 sets of 10-30 reps, or can be done for a prescribed time, or for prescribed work-rest intervals.
The plank march can be done by only lifting the legs as an introductory variation, and weights can be held in the hands.