Tendon stiffness, running biomechanics and performance

Peter Malliaras27th of March 2016home / blog / tendinopathy-updates / tendon-stiffness-running-biomechanics-and-performance

Dear all

Welcome to tendinopathy blog 13. My 1 hr lecture on ‘Modern Tendinopathy Management’ is out and has been really popular so far - thanks to those who have  watched and commented. You can download it free.

The blog theme this week should be ‘going off on tangents’. We look at a study investigating running initial contact angles and the link with tendon stiffness, it’s fairly straight forward but brings up lot’s of interesting biomechanics discussions and tangents! There is also a systematic review of studies on surgery for midportion Achilles tendinopathy.

Courses in the UK in June have now sold out, and just a few places left in Melbourne end of April.

Hope you enjoy

See you next time



Optimising tendon stiffness for performance – is it related to initial contact angles?

What they did: Keitero Kubo is one of my favourite researchers in the area of tendon adaptation – he and his team have done lot’s of great work over the years. In this study Kubo et al. investigate the relationship between knee and ankle tendon stiffness and knee and ankle angles at initial contact (IC) in running. They suggest that when considering the knee, people that land with a straighter knee may have greater vertical ground reaction forces (Potthast et al. 2010), so they develop stiffer knee tendons. They have shown in one of their prior studies that a stiffer knee vastus lateralis (VL) tendon was associated with better 5000m running performance (Kubo 2015). In this study they wanted to see whether knee angle at contact was in fact related to tendon stiffness (due to habitual increased loading). They also investigated whether ankle angle at IC was associated with Achilles tendon stiffness, even though they had previously shown that Achilles stiffness was not associated with foot strike (which is related to ankle angle at IC) among trained 5000m runners (Kubo 2015). People that heel strike tend to land with more ankle dorsiflexion, although knee angle is not clearly related to footstrike (Barton et al. 2016) – see figure below of 2 heel strikers with really different knee flexion at IC.

 Screen Shot 2016-09-08 at 1.59.01 pm.png

They took 32 highly trained long distance runners – with 5km PB’s over the last year ranging from 14:11 to 16:15 (14:54 ± 0:26) minutes. They ran on a treadmill at 14, 16 and 18 km/hr and 2D video was used to assess knee and ankle angles at contact. They also measured vastus lateralis (VL) and medial gastroc (MG) muscle-tendon junction strain during maximal voluntary contraction and used this to estimate the stiffness of of the VL and MG tendons/aponeurosis (see last weeks blog for how you calculate stiffness in this way).

What they found: There was no correlation between either the knee joint angle and VL aponeurosis/tendon stiffness, or the ankle joint angle and medial gastroc aponeusosis/tendon stiffness. Best 5000m race time was not associated with knee or ankle angle at initial contact. The low and nonsignificant correlation between knee and ankle angle at IC (see figure below) suggests lots of variation in the way elite runners land – suggesting a lack of ideal style.

 Screen Shot 2016-09-08 at 1.59.18 pm.png

Clinical interpretation: Running performance was not clearly associated with knee or ankle angles at IC – this is not surprising because many other factors influence performance such as optimising leg stiffness and minimising braking forces. Just like with foot strike – we know elite runners are more likely to land midfoot/forefoot and perform better than non-elite runners who are more likely to heel strike (Kasmer 2013, Hasegawa 2008). This doesn’t mean switching to midfoot strike is the only factor to consider – optimising leg stiffness, and training the muscle-tendon unit to maximise effectiveness of stretch-shorten cycle are also important, among other factors.

What I am more interesting in is the other part of this study - tendon stiffness did not appear to relate to knee and ankle angles. So why not? The authors argument was that if runners habitually landed with a straighter knee they would 1) load their knee more so have a stiffer tendon; and 2) have better running performance because of the link between VL tendon stiffness and running performance. Let’s deconstruct these 2 points…

First, landing with a stiffer knee does not tell us much about knee tendon load, despite the fact that vertical ground reaction force may be higher. Knee tendon load is obviously related to how ground reaction force is absorbed throughout the kinetic chain and throughout stance – so it is not surprising this variable was not associated with VL tendon/aponeurosis stiffness. Kubo et al. suggest one reason they did not find an association may be because tendon is less likely to adapt to energy storage/release loads like running (see last weeks blog for detailed discussion of this), but we know that habitual runners do show signs of tendon adaptation (e.g. Rosager et al. 2002), probably just needs to be applied for long enough ie years.

Second, what do we actually know about the link between tendon stiffness and running performance? The main thing you notice when you delve into the literature is that it is certainly not straight forward! The authors own studies and others suggest that that less stiff tendons, particularly Achilles (Kubo et al. 2015 – in 5000m runners, Stafilidis et al. 2007 – in sprinters) may be advantageous for performance. Evidence for the knee extensors is conflicting, (Kubo et al. 2015 – greater stiffness better, Kubo et al. 2010 – lower stiffness better. Both in elite long distance runners).

So how do we explain these findings? I must declare I am not an expert in this area, but here goes and would love to hear from you if you have a different interpretation. During stretch-shortening cycle, the tendon can be a power amplifier by storing and releasing energy quickly. The optimal tendon stiffness to maximise performance depends on task. Trained people like sprinters and runners tend to have stiffer tendons that can stretch/recoil quickly and more effectively under higher load (because they habitually endure higher loads), when compared to untrained people (e.g. Kubo 2000-stiffer VL in long distance runners vs untrained, e.g. Arampatzis 2007-stiffer Achilles in sprinters vs endurance trained and controls). However, when comparing to themselves, ie taking group of trained athletes, it seems there may be some advantage of having a tendon that is less stiff (but still stiffer than an untrained persons). Make sense? The tendon needs to be stiff enough to cope with the high loads in for example sprinting, but compliant enough to absorb and release energy. Also remember that a tendon is only as good as its accompanying muscle. Sprinters for example require huge rate of force development and muscle capacity to resist inertia on impact and contract strongly so the tendon is able to stretch and store energy.

Also, the muscle-tendon unit ‘design’ will influence tendon stiffness. Steve Pearson put’s it very nicely in this 2012 paper: ‘The muscle can work minimally to provide maximum efficiency or in a manner to generate optimal velocity for maximum power at ideal muscle lengths for maximal force generation’. Shorter/stiffer tendons with longer fascicles facilitates the latter (ie maximal force generation), like for example around the hip, as apposed to the longer/less stiff Achilles tendon that strains to allow the short calf fascicles to operate efficiently in an optimal range (see figure below – parts of the hamstrings have long fascicle lengths (FL) relative to muscle length (ML), whereas planterflexors have short FL relative to ML.

 Screen Shot 2016-09-08 at 1.59.30 pm.png

Take home message: 1=IC contact angles alone seem to have limited bearing on 5000m running performance; 2=the complexity of muscle-tendon unit function is fascinating, and tendon tissue (passive) stiffness is probably tuned to task for elite athletes, but so is muscle stiffness (neuromuscular) and probably architecture. (not to mention other factors such as leg stiffness, contact time, etc that I have not gone into in detail in this blog). This complex function demands that during tendinopathy rehab we consider not only tendon and muscle loading but also developing stretch-shorten cycle efficiency specific to task.


What is the best surgery for midportion Achilles tendinopathy?

What they did: My answer to the title question would be none! Try and avoid surgery as most people I'm sure do. But in some cases it may be indicated. Baltes et al. have systematically reviewed the literature on midportion Achilles tendinopathy surgery. They included all studies investigating surgical treatment for midportion Achilles tendinopathy, but they excluded studies that had less than 10 participants.

What they found: surgeries performed in the 23 studies could be grouped into five categories. 11 studies investigated open techniques, 7 studies minimally invasive, 3 studies endoscopic, 1 study gastrocnemius lengthening, 1 study performed open resection followed by interposition of FHL tendon. Open surgeries generally consisted of release of the tendon (removing adhesions and paratenon), debridement of degenerative tissue, and/or longitudinal tenotomy. Studies included where either case series or compared surgical techniques. None of the included studies compared surgical treatment with nonsurgical treatment or placebo intervention or wait and see.

There was a large variation in ‘success rates’ (range 69-100%) for all techniques (ie was hard to tell them apart – see table below). Mini-invasive and endoscopic techniques result in lower complication rates. Of a possible 33, the median Down and Blacks quality score of the included studies was 12 (IQR 10.0–13.25), so relatively poor study quality. Mini-invasive surgery mostly involved release of the Achilles tendon and excision of the plantaris. In the Tallon 2001 review from 15 years ago they found a negative correlation between between success rate and methodological quality of the studies. In this review they did not, but they did find a positive correlation between year of publication and quality score, which is a good thing, study quality is improving!

Screen Shot 2016-09-08 at 1.59.42 pm.png 

Clinical interpretation: Success rates were between 69-100% (only in surgical studies do you get 100% success!). There was no clear difference between surgical techniques. What is interesting to me is that you can do vastly different procedures and get similar outcomes, much like rehabilitation evidence (see my recent lecture on Modern Tendinopathy Management where I talk about this phenomenon). Doing something, anything, seems to have some effect. The mechanisms are probably complex...placebo? taking a long break from load? etc

What does come out of this study is that the key factor with surgery may be to avoid doing harm, ie complications, and for this the mini-invasive surgeries seem better. In the clinical setting, surgery for midportion Achilles tendinopathy is very rare, most people will respond to loading and conservative management if given enough time. I tend to see surgical failures and what is striking is that they often have a different presentation, features of central sensitisation. In fairness to the surgeons, I am sure they see my failures too – it goes both ways!

Untul next time, keep joining the dots


Peter Malliaras
Tendinopathy Rehabilitation