Why tendons heal slower with age: cause identified

Tendons connect muscles to bones and are under constant mechanical load. With aging, their composition changes. The study began with an analysis of global trend data: tendon injuries declined between 1990 and 2021, likely because physically demanding work has decreased in many countries. But in older adults, the risk remains high even without heavy labour.

The researchers took tendons from young (eight-week-old) and old (18-month-old) rats of both sexes and examined how they responded to repeated stretching. They found that the expression (production) of two proteins in the extracellular matrix (the structural tissue surrounding cells) declined sharply with aging: Col1a1, the building block of type I collagen, and Sparc, a regulator of collagen maturation. This applied to both male and female rats.

Sex differences in how tendons age

Notably, the way tendons age differed between sexes. In female rats, tensile strength decreased with aging; in male rats, tendon weight and tensile strength actually increased. Cell composition also changed differently: in females, fibroblasts (cells that produce matrix) declined; in males their proportion increased. This suggests that hormonal and cellular mechanisms drive tendon aging in a sex-specific manner.

The researchers also found that a promoter (a DNA switch that activates the production of genes) regulating both proteins simultaneously could improve tendon quality in rats. But this is an early mechanistic insight and far from a clinical application in humans.

Implications for recovery in older adults

This research contributes to understanding why tendon injuries heal more slowly and recur more often in older people. It points to the extracellular matrix as a starting point for future research into tendon repair in aging. Whether this holds in humans requires follow-up studies in human tissue and, ultimately, clinical research.

Read the original article