Treadmill running increases Achilles tendon force

Hi All,

Welcome to tendinopathy blog 22.

Very pleased to announce a new course series – Mastering Lower Limb Tendinopathy – 1.5 days of practical on assessment/management of tendinopathy with an additional 3 hours of video content. The Aust Physio Association is running them but you can come along as a physio or non physio (myo, exs phys, chiro, osteo, pod, Pilates people). For details go to this page and search ‘lower limb tendinopathy’ for dates in every Australian state.

Some great stuff in the blog this week (Subscribe here). First a paper by Rich Willy et al. comparing patellofemoral and Achilles loads in overground and treadmill running – brings up some interesting questions for running rehab among Achilles patients. Then we have a huge review of exercise and ageing effects on tendon. Although their focus on normal tendon some messages there for loading tendinopathic tendon.

Hope you enjoy

See you next time

Peter

Treadmill running increases Achilles tendon force

What they did: This is a simple but very clinically useful study by Rich Willy et al. Rich (twitter: @rwilly2003) is prolific running researcher and physical therapist, currently at East Carolina University. This study compares patellofemoral joint and Achilles tendon forces in overground and treadmill running. When people run on a treadmill generally reduce step length and knee flexion. This may reduce knee loads but if people take more steps (higher cadence) cumulative knee load may increase. Ankle loads have been shown to increase so maybe Achilles loads would to.

18 volunteers (9 men, 9 women) participated in the study. Participants were between 18-35 – they restricted age to limit any age effect on biomechanics. All participants ran at least 10km/week and felt comfortable running on a treadmill. After warm up they measured running biomechanics at self-selected speed, first on the treadmill and then overground in the lab. They chose to run people on the treadmill first because self-selected speed is often higher overground, and this may not be safe/comfortable on the treadmill. They measured forces and 3D motion and used a biomechanical model to derive peak load, rate of loading and estimated cumulative load per 1 kilometer of continuous running for the patellofemoral joint and Achilles tendon. Planterflexor moments and Achilles tendon moment arm were used to derive Achilles force. PFJ stress was estimated based on PFJ reaction force (based on quads force and knee joint angle) and known sex-specific contact areas.

What they found: Self-selected speeds were well matched on the treadmill and overground. On the treadmill they tended to have shorter step length, similar stance time, and peak knee flexion and peak ankle dorsiflexion were not significantly different. Peak knee extensor loads, and PFJ peak force, rate of loading and estimated cumulative force per 1 kilometer of continuous running were not different between overground and treadmill. In contrast. treadmill running resulted in 14.3% greater peak planterflexion moment, 21.5% greater peak Achilles tendon force, 15.6% greater loading rate of the Achilles tendon, and 14.2% greater estimated cumulative load 10 per 1 kilometer of continuous running (moderate to large absolute effect sizes). See graphs from paper below showing kinetic but no kinematic differences at the ankle.

Clinical interpretation: The study findings suggest that peak knee/ankle kinematics are similar, as are PFJ loads, but Achilles loads are higher on treadmill vs overground running. So the subtle change in terms of reduced step length (and probably increased cadence) did not change kinematics at the ankle but did change forces. A good reminder that kinetics do not always correlate with kinematics! Important findings for clinicians advising Achilles patients on return to running – Achilles patients often ask whether treadmill running was ok, and of course it is for many but for the more irritable ones you may consider overground running – as always comes down to load tolerance. But also consider the individual kinematics, step length and cadence of your patient on treadmill vs overground as there is lots of inter-subject variability.

Aging and exercise effects on tendons

What they did: Svensson and co-authors are part of Michael Kjaer’s tendinipathy research group in Copenhagen, and they have reviewed the effects of aging and exercise on the tendon. They too are a prolific bunch – many of the studies they review are from their group, so they have a descent understanding of the literature! Here are the key points related to aging and exercise, with some discussion to follow.

What they found: effects of aging

• Decrease cell number and activity but mainly during maturation rather than aging
• Decrease number of stem cells with aging
• Limited collagen turnover after maturation (age 17)
• There does not appear to be atrophy with age as you get in muscle
• The only consistent compositional change with age is the accumulation of non-enzymatic cross-links (advanced glycation endproducts)
• Paradoxically tensile stiffness seems to decrease, although findings are conflicting

What they found: effects of exercise

• Loading leads more growth factors and matrix proteins (mechanotransduction)
• The effect is modest in humans compared to maturing animals
• Hypertrophy may occur in the outer tendon
• The authors speculate that tendon growth occurs through addition of ‘external layers’
• Short term (12 weeks) heavy load seems to lead to increased tensile stiffness
• Long term (years) sport loading seems to lead to increased cross sectional area
• Enzymatic cross links increase and non enzymatic decrease

The key effects of exercise are summarised in the graphs below.

Clinical interpretations: As the authors discuss, one of the limitations of stiffness adaptation is not knowing whether it is positive and helpful. Read this previous blog for discussion of the relationship between tendon stiffness and performance/function. Another issue the authors discuss is whether cross sectional area adaptation is related to increased collagen content or is it simply increased water content – this is not clear in all studies.

On a positive note, this review summarises an absolutely mammoth amount of data. The key messages for me are 1) tendon hypertrophy seems to occur on the outside of the tendon – the authors propose that external layers are added which is a nice way to think about it; 2) exercise may reduce some of the potentially detrimental effects of aging, such as reduced tensile stiffness and increased non-enzymatic crosslinks. In a previous blog I have discussed the Bohm review which reviews tendon stiffness adaptation with different types of loading e.g. isometric, isotonic, and plyometric. So over all tendon structure as well as mechanical properties change with load. Of course much less is known about pathological tendon, but it is conceivable to think there is still potential for adding ‘external layers’ around the pathological area.