Final answer:
The maximum percentage that muscles can stretch or shorten is confined to between 80 and 120 percent of a sarcomere's resting length for optimal tension production. Going beyond these limits reduces the muscle's ability to generate force. Efficient muscle use involves the recruitment of motor units in a way that balances force production and energy expenditure.
Step-by-step explanation:
The maximum percentage that muscles can stretch or shorten relative to their length is largely dependent on the optimal length-tension relationship within the sarcomere, the basic functional unit of a muscle fiber. When considering skeletal muscle, the sarcomere exhibits the greatest potential for tension and thus force of contraction when it is between 80 percent and 120 percent of its resting length, with maximum tension usually occurring at 100 percent. Beyond these limits, the muscular force diminishes significantly. Stretching beyond 120 percent leads to inadequate overlap of thick and thin filaments, making cross-bridge formation, and thus tension, diminish. Conversely, shortening below 80 percent causes interference among the adjoining filaments and a reduction in tension as well.
Motor unit recruitment plays a crucial role in muscle contraction, and while maximum force can be produced by activating all motor units simultaneously, this state is unsustainable due to high energy demands. Instead, muscles use asynchronous motor unit activation to prevent fatigue and maintain contractions.