UCL study reveals more about our Achilles heel

It's a discovery that seems counter-intuitive but researchers from UCL and Liverpool University have found that tendons in high-stress and strain areas, like the Achilles tendon, actually repair themselves less frequently than low-stress tendons. The study, led by Dr Helen Birch (UCL Centre for Stem Cells and Regenerative Medicine) and published in this week's Journal of Biological Chemistry sheds some light on the increased susceptibility of certain tendons to injury during ageing. Tendons, composed of collagen and other proteins, connect muscle to bone and are therefore vital for movement. Considering their strenuous activity, tendons need to be continually repairing collagen damage to avoid build-up of degraded proteins that could cause serious complications. Not all tendons are equal though; some tendons, such as those in the hand, are primarily used to maintain proper limb placement while others, including the Achilles tendon in humans and the superficial digital flexor tendon (SDFT) in horses, have to bear a lot of weight and strain. It would be expected that high-strain tendons would repair more frequently, but Dr Birch and colleagues examined protein turnover in the tendons of horses of various ages and found that the high-strain SDFT (located at the rear of the limb) repairs much less frequently than the low-strain common digital extensor tendon (CDET, located at the front of the limb). Birch and colleagues used an approach called amino acid racemization to measure protein age in the horse tendons.