Human Achilles tendon: Absence of renewal during adult life revealed by nuclear bomb 14C

Tendons connect muscle to bone and transmit enormous, repetitive forces during movement. The prevalence of tendon overuse‐injuries is high, and these conditions are often prolonged due to inadequate tissue regeneration. Whether this relates to a slow tissue turnover is unknown since current methods provide diverging estimates of tendon protein half‐life that range from two months to 200 years. With use of the bomb pulse method we have studied life‐long Achilles tendon turnover and can show that human core tendon tissue is practically inert during adulthood. The extremely slow turnover of adult tendon is demonstrated by tissue concentrations of radiocarbon ( 14 C), corresponding to the elevated atmospheric levels left over from nuclear bomb tests in 1955–1963, decades before the tendon tissue was sampled. We find that tendons contain a concentration of 14 C approximately reflecting the atmospheric levels during the first 17 years of life, indicating that tendons are formed during height growth, but are essentially inert thereafter. Our observations resolve a basic question in tendon physiology and firmly disprove previous suggestions that tendon tissue is turned over at a rate comparable to the fast turnover of skeletal muscle. The absence of tendon tissue renewal during adulthood is a fundamental premise for understanding tendon function and for future research in tendon pathology and treatment of tendon injury.