What principle states that for every action there is an equal and opposite reaction?

The principle stating that for every action there is an equal and opposite reaction is known as Newton's Third Law of Motion. This law describes the relationship between forces in interactions between two objects. When one object exerts a force on a second object, the second object simultaneously exerts a force of equal strength in the opposite direction back on the first object. This foundational concept in physics helps explain a wide range of phenomena, from the propulsion of rockets to the way swimmers push off the pool wall.

In the context of fitness and biomechanics, understanding this principle can help trainers and athletes improve their performance. For instance, when a runner pushes against the ground, the ground pushes back with equal force, enabling propulsion. This principle is crucial for developing techniques that maximize efficiency and power during various movements in sports and exercises.

The other options reflect different laws of motion or concepts but do not capture this specific relationship between action and reaction. Newton's First Law describes inertia, while the Second Law relates force, mass, and acceleration. The Law of Universal Gravitation pertains to the gravitational attraction between masses, making each option distinct from the concept articulated in Newton's Third Law.