Achilles and patellar tendon injury (tendinopathy) is common and difficult to treat. Up to 18% of runners may develop Achilles tendinopathy, i.e. approximately 1 in 5. Elite runners have it much worse, up to 50% may have Achilles tendinopathy. Elite and sub-elite jumpers (volleyball, basketball) also have an alarmingly high prevalence of patellar tendinopathy, about 40-50%. First line treatment usually involves eccentric training – success rates for this intervention range between 55-89% in the Achilles and 50-70% in the patellar. There are many potential reasons for the range in success rates, including different populations, study designs, and the actual rehabilitation protocol.
I have just returned from the UK where I worked in a multidisciplinary specialist tendon clinic in London where we would treat 300 Achilles and 200 patellar tendons every year. Based on lessons learnt from this clinic, some key basic science and clinical research, I would like to present an argument for high load as one of the key components of a successful tendon injury treatment program.
Achilles the warrior was akin to a high performance athlete. It is ironic that his heel was his ‘weakest link’ as undoubtedly it would have been key in allowing him to achieve his legendry warrior status, in the same way that the Achilles tendon was indispensable to Jonathan Edwards in setting his triple jump world record (18.29m) in 1995. The Achilles and patellar tendons act as very efficient springs during fast human movement. They absorbenergy when they are stretched and this energy is released and enhances muscle power in the muscle shortening phase and increasing the efficiency of human movement. This so-called stretch-shortening cycle only occurs with faster movements, such as running, jumping, but also walking. The stretch-shortening cycle is a fantastic mechanism in regards to human movement and performance but it does have consequences. Stretch shortening cycle activities lead to very high tendon loads and greater stimulus to tenocytes (tendon cells) than slow muscle contractions, increasing the potential for tendon overuse injury.
The magnitude of load that the Achilles and patellar tendons endure during fast (i.e. stretch-shortening cycle activities) is astonishing.The Achilles tendon sustains up to 8 times body weight during running whereas up to 10-15 times body weight is sustained by the patellar tendon during maximal jumping/landing and weightlifting. It is no surprise, then, that we tend to see Achilles and patellar tendinopathy in groups who endure prolonged and/or intense periods of stretch-shortening cycle activity (basketball, volleyball, running, sprinting, etc). Achilles tendinopathy also commonly affects sedentary people who’s only activity is walking. This is because walking is a stretch-shortening cycle activity involving Achilles loads of 2-3 times bodyweight.
We have established that tendons sustain high loads in stretch shortening cycle activity and this may increase injury risk, but how does this influence rehabilitation? One of the key goals of rehabilitation should be to increase tendon stiffness, as this will increase the tendons ability to withstand repeated stretch shortening cycle loading and overuse injury. It is also important because painful and pathological tendons have reduced tendon stiffness and this will reduce their ability to act like a spring. The question is, what is the stimulus for increasing tendon stiffness? There is some evidence that tendon responds more to heavy rather than lighter rehabilitation loads. In a study published in 2005, Keitaro Kubo and his team compared patellar tendon response when performing 6×15 second isometric contractions for 12 weeks in both 50 degrees and 100 degrees. The tendon moment arm and therefore force was greater at 100 degrees and only at this angle did the tendon display an increase in stiffness – i.e. it became stronger! There are many other studies that suggest an increase in tendon stiffness after heavy slow resistance training. In 2008 Nele Mahieu published a study investigating eccentric training with bodyweight in the Achilles tendon and did not find an increase in tendon stiffness after 6 weeks. This research is mainly among people with normals tendons so we’re not able to draw any conclusions about tendinopathy patients. However, there does seem to be a clear suggestion that high load is probably more likely than bodyweight exercise to increase tendon stiffness.
After all, high load is exactly what Hakan Alfredson has advocated from the start. The title of his landmark 1998 publication on Achilles eccentric training was: ‘Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. I have lectured to hundreds of physiotherapists in the UK about tendinopathy and my impression is that over time the benefit of Alfredson’s eccentric training program has been attributed to the mode of contraction (i.e. eccentric) rather than the load. A study published in 2009 by Mads Kongsgaard and co-workers in Denmark compared eccentric training and concentric-eccentric heavy slow resistance training (greater maximal load) and found no clinical difference between the groups at 12 months. The concentric-eccentric heavy slow resistance group was more satisfied – probably because they only had to perform the exercise 3x/week rather than 2x/day!! This study suggests that eccentric mode of contraction may not be essential for a good clinical outcome among some groups.
There is no doubt that some patients with Achilles tendinopathy respond to eccentric training with bodyweight. One thing we know about eccentric training without load is that it may lead to a more compliant and more flexible joint – this was shown in the study by Nele Mahieu discussed above. So perhaps, when performing eccentric training with bodyweight it is more of a muscle stretch than tendon specific intervention, and this may be sufficient for some patients (perhaps those that are very tight). I suspect in the future, when we have more evidence, we may sub-group our patients into groups who respond more to stretching vs heavy loading.
What about patients who are less active, older, overweight or have very severe pathology, do we still need to load these patients heavily? Maybe their tendons have less capacity to adapt and become stiffer. Obviously clinical discretion is important. Weakness and/or pain may limit heavy loading in some groups.
So, in essence, there is some evidence that slow, heavy loading is good for tendons – especially the big, strong power tendons of the lower limb. High load is not a panacea for tendinopathy, just in the same way that eccentric training is not, but it is something to consider with Achilles and patellar tendon injury treatment among some patients.
Alfredson, H., Pietilä, T., Jonsson, P., Lorentzon, R. (1998) Heavy-Load Eccentric Calf Muscle Training For the Treatment of Chronic Achilles Tendinosis. 26, 360-366.
Kongsgaard, M., Kovanen, V., Aagaard, P., Doessing, S., Hansen, P., Laursen1, A., Kaldau, N., Kjaer, M., Magnusson, S. (2009). Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy, Scandinavian Journal of Medicine & Science in Sports, 19(6):790-802.
Kubo, K., Ohgo, K., Takeishi, R., Yoshinaga, K., Tsunoda, N., Kanehisa, H., & Fukunaga, T. (2006). Effects of isometric training at different knee angles on the muscle-tendon complex in vivo. Scandinavian Journal of Medicine & Science in Sports, 16, 159-167.
Mahieu, N., McNair, P., Cools, A., D’Ahaen, C., Vandermeulen, K. & Witvrouw, E. (2008). Effect of eccentric training on the plantar flexor muscle-tendon tissue properties. Medicine & Science in Sport & Exercise, 40, 117-123.