Question

Why does this specific type of relationship between the amount of stretch and the amplitude of the contraction occur? How does this change in length affect the numbers of cross-bridges that form in the different areas of your graph? Be specific.

Answer 1

The specific type of relationship between the amount of stretch and the amplitude of contraction is Length–Tension Relationship.

The force with which muscle contracts depends on the length of sarcomeres within a muscle before contraction begins. At resting length of sarcomere, the overlapping zone is optimal and the muscle fiber can develop maximum tension. When the zone of overlap between a thick and thin filament extends from the edge of the H zone to one end of a thick filament, maximum tension (100%) results. With an increase in stretch of muscle fibers, the zone of overlap shortens. As a result of which fewer myosin heads can make contact with thin filaments and leads to a decrease in tension. When a skeletal muscle fiber is stretched to 170% of its optimal length, there is no overlap between the thick and thin filaments. The tension becomes zero because none of the myosin heads can bind to thin filaments. With a further decrease in sarcomere lengths, the tension decreases because thick filaments crumple as they are compressed by the Z discs, resulting in fewer myosin heads making contact with thin filaments. The resting muscle fiber length is optimized by firm attachments of skeletal muscle to bones and to other inelastic tissues.