"You are Already My Friend": Earth Pony Martial Arts · 6:28pm Dec 18th, 2019
According to Lauren Faust, Earth Ponies draw on the life energy of the planet itself to fuel their abilities. This ranges from super strength and endurance, to communication and control over flora and fauna, to Earth bending, healing, increased longevity (Granny Smith is easily two centuries old) and enhanced sensory perception (Pinkie Sense).
In other words they are using life energy. Or as is known in real life martial arts, ki.