Titin: The Largest Protein in the Human Body: & Why Almost Zero Doctors Know About It. Titin is largest protein we have discovered thus far in the human body, was discovered in the 1970’s, is the third protein in sarcomeres, and is the reason eccentric muscle contraction is stronger. Good thing we are still taught today that there is no apparent reason eccentric contraction produces more force than isometric or concentric contraction. Cross-bridges alone cannot account for energy absorption during active stretch. Even after accounting for tendon, thick filament, thin filament, and passive titin elasticity, only about 34% of the absorbed energy could be explained. The extra tension that remains after stretch is due to titin. Most of the absorbed energy during stretch is stored in non-cross bridge structures, mainly titin.