Final answer:
The relaxation phase is when the muscle tension decreases due to the release of actin-myosin cross-bridges, facilitated by a decrease in Ca2+ levels in the sarcoplasm, which allows muscles to stretch and reduces co-contraction.
Step-by-step explanation:
The stage that includes the release of degrees of freedom, allowing for less co-contraction of the agonist and antagonist, refers to the relaxation phase after a muscle twitch contraction. This is when the tension in the muscles decreases as a result of the interaction between actin and myosin, the sarcomere structures, and the role of calcium ions (Ca2+) in the sarcoplasm. During a contraction, actin and myosin form cross-bridges facilitated by Ca2+, which are disrupted when ATP binds to the myosin head, causing it to release from actin and allowing the muscle to relax. During this relaxation phase, stored free energy from ATP hydrolysis that was previously held in the high-energy myosin conformation is released, enabling the muscle fibers to return to their resting state. The decrease in Ca2+ concentration, due to its reuptake into the sarcoplasmic reticulum, reduces the interaction between actin and myosin, thus completing the relaxation phase and allowing for the muscles to stretch and lessen co-contraction.