The plane that divides the body into front and back halves, containing every movement that travels side to side.
Also called the coronal plane. Abduction and adduction happen here: lateral raises, lateral lunges, side planks, adductor and abductor machine work, and the sideways step of a crossover.
It is the plane most strength programs skip. Sport does not: a change of direction, a stumble caught on one leg and a bag carried in one hand are all frontal-plane loads, and hip abductor strength is what stops the knee falling inward under them.
Two sets of a lateral lunge and two sets of a suitcase carry, twice a week, is enough for most general clients. Load the carry properly, around a quarter of bodyweight per hand for 30 metres, or it is a warm-up rather than training.