Final answer:
The term describing the concept that muscles gain more strength with the greater load they lift is known as 'progressive overload.' This requires increasing the intensity of exercises for continued muscle growth and strength gains, and is based on the recruitment and contraction of muscle fibers.
Step-by-step explanation:
The term for the principle that the greater the load placed on a muscle and the higher the force contraction it produces, the more strength that muscle will gain, is often referred to as progressive overload. This principle lies at the heart of effective strength training. Progressive overload necessitates a continuous increase in the intensity of the exercise to achieve muscle growth. For muscles to adapt and become stronger, they must be subjected to stresses greater than what they are accustomed to. When lifting weights, if the load is not progressively increased, muscle size will not increase significantly. As a muscle adapts to a given load, it requires an even heavier load for further strength gains.
The foundation of this concept is based on the muscular force produced by the contraction of muscle fibers, where sarcomeres within the fibers shorten to generate tension. A muscle fiber is either fully contracted or not at all, and the number of fibers contracting at once will determine the strength of the muscular force. As the muscles face a heavier load, more muscle fibers are recruited to generate the necessary force. To further increase force production, frequency of action potentials can be raised, inundating the muscle with calcium and boosting the formation of cross-bridges between actin and myosin in the muscle fibers, essential for muscle contraction.