Essential guide to tendons

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What do tendons do?

Tendons connect muscle to bone, transmitting the force generated by muscles to move your joints – and hence your body. But tendons are far more than just cables. They are active, responsive and vital partners with your muscles, so much so that the two tissues are regularly referred to as a muscle-tendon unit. Muscles don’t end where tendons begin. There is no line drawn. Instead, there is a transition area, the muscle-tendon zone, where muscle gradually gives way to tendon. In this zone, muscle fibres and tendons merge, operating as a unit. It is only at the outskirts of this zone that tendons finally emerge as the glistening, white, fibrous cords that eventually connect to bone.

Where do things go wrong?

The point at which individual muscle fibres meet a tendon is your muscle’s weak link. It’s here that most muscle strains occur. Powerful eccentric contractions cause damage either at this junction or directly above it. If you’re lucky, damage will be limited to a few fibres and shortlived soreness. If you’re unlucky, a complete muscle tear might require surgery. The good news is that the muscle-tendon zone gets a rich blood supply, resulting in a healing rate that almost parallels that of muscle.

Achilles tendon injuries, the plague of runners (especially those aged 40+), range from mild tendinitis to complete rupture. Achilles tendinitis is an overuse injury marked by by painful inflammation. Achilles tendinosis, on the other hand, involves degenerative damage at the cellular level that produces chronic pain without inflammation. Until the late 1990s, almost all Achilles pain was thought to result from tendinitis. Now, it’s understood that most Achilles pain is generated by tendinosis.

The best treatment for Achilles tendinosis is eccentric heel dips, a remedy discovered by Swedish orthopaedic consultant and runner Hakan Alfredson. When Alfredson developed severe Achilles pain, his boss refused to operate on the grounds that the clinic couldn’t afford to have him on sick leave. So, desperate for the operation, Alfredson attempted to rupture his Achilles with a high-volume bout of heel dips. Instead, he got better.

For a study investigating the long-term effects of heel dips, researchers questioned patients who’d previously treated their Achilles tendinosis with 180 heel dips per day for 12 weeks. The study, published in the British Journal of Sports Medicine, found almost 40 per cent of the patients remained pain-free five years later. The researchers also noted that two similar studies on the long-term effect of heel dips showed even better results, with 88 per cent and 65 per cent reporting little or no pain. It’s not calf strengthening that does the trick. It’s stress on the tendon itself, and subsequent adaptations, that lead to healing.

In the absence of proactive treatment (such as heel dips), damage done to tendons in the white fibrous zone – a bloodless stretch preceding the interface with bone – has a gloomy outlook. Recent Danish research tried to determine the tissue turnover rate (the time it takes to regenerate completely new tissue) for this zone. Previous estimates had ranged from two months to 200 years. So when can you expect damaged this type of tendon tissue to regenerate? According to the Danish study, almost never.

How can I protect my tendons?

Running and resistance-training exercises contribute to tendon stiffness. These wobble board and resistance band exercises strengthen the entire kinetic chain (muscles, connective tissue and nerves from hip to toe); this helps to prevent tendon inflammation and damage. Active isolated stretching is useful for working the muscle-tendon zone because it sidesteps the stretch reflex that can lead to strains in this area.