The medicinal properties of eccentric muscle contractions

Eccentric exercises (EEx) are well known in resistance training (RT) 1, injury prevention and rehabilitation and (chronic) disease management. Eccentric training in rehabilitation has long been a subject of controversy as EEx are prone to elicit strong muscle damage, subsequent soreness (DOMS) and impaired muscle functioning. Exercise-induced muscle damage (EIMD) and the hypothesis that EIMD is necessary for muscle growth would render EEx unfeasible for rehabilitation purposes: damage caused by EEx in the presence of musculoskeletal injuries would be downright harmful. Muscle damage as a necessary precursor for muscle growth has been challenged by research demonstrating muscle restructuring, e.g. hypertrophy, happening without discernable damage 2,3. Furthermore, eccentric training can occur without muscle damage if appropriately dosed.

3d rendered illustration of the achilles tendon

Eccentric exercises for the management of common tendinopathies

Appropriate loading of diseased tendons with exercise therapy (ET) to improve pain and function is common therapy practice. ET for treating tendinopathies of the lower limbs may consist of different mode of contractions, various exercises, dose and intensity. A systematic review on the effectiveness of different types of ET for lower limb tendinopathies is on its way4. With regards to ET and other modalities – such as low-level laser, extracorporeal shockwave, platelet-rich plasma injections and corticosteroids – for the treatment of most common tendinopathies of both lower and upper limbs, research consistently demonstrates the superior treatment effects of EEx for self-reported function and tendinopathy-related pain 6.

No pain, no gain?

Tendon pain during EEx is normal and may even be critical for improving pain and function in tendinopathies of the patellar and Achilles tendon 5,7,8. To improve pain and function in patellar tendinopathy, EEx should promote tendon pain greater than 0 and less than 5 on a 0-10 pain scale for a single leg decline squat 9. Two recent narrative reviews again highlight the importance of pain sensation for rehabilitation with reference to the earlier research by Alfredson and colleagues 9,10 albeit this early research is not critically discussed.

EEx in Achilles tendinopathy

In 1986, Stanish and colleagues were the first to implement EEx for Achilles tendon pathology 11. Stanish believed that tendon tissue pathology should be treated with high loads. He realized that EEx could increase the load on muscle and tendon tissue compared to concentric exercises. In 1998, Alfredson and colleagues demonstrated short-term beneficial effects of heavy-load eccentric calf muscle training (heel drop exercises) for Achilles tendinosis on pain and function in recreational runners 7. A 2015 RCT evaluated the effectiveness of EEx with heavy slow resistance training (HSR) for patients with midportion AT. Results showed no difference in beneficial effects on pain, function and sporting activity as measured by the visual analog scale (VAS) and the Victorian institute of Sports Assessment – Achilles (VISA-A). Also, patients tended to prefer the HSR over EEx after 12 weeks but not after 52 weeks 12. A systematic review and meta-analysis (SRMA) of 19 studies reported on the benefits of EEx for mid-portion Achilles tendinopathy (AT) 13 and a more recent SRMA sought to provide clinicians with information regarding pain perception and improvement of pain and function in patients suffering from mid-portion AT after performing different eccentric loading protocols. Pain and function acutely improved which would negate proposed mechanisms such as increased contractility and hypertrophy of muscle fibers which – obviously – take time, i.e. changes in these mechanisms are not observable or measurable immediately following EEx. The SRMA allows clinicians to educate their patients with mid-portion AT on average healing time and long-term course of treatment 14. Another recent narrative review contemplated as to whether EEx are a magic bullet for AT. The authors conclude that EEx and other mode of contractions with concomitant loading protocols – as well as different modalities, such as ankle orthoses, whole body vibration and shockwave therapy combined with EEx or alone – are effective in reducing pain and improving function. The authors appreciate that ‘appropriate load modification and exercise prescription’ requires ‘systematic clinical reasoning and incorporation of patient values to optimize outcome’ 15.

EEx in patellar tendinopathy

A common overuse condition, mainly seen among runners and athletes who participate in jumping sports, patellar tendinopathy (PT9 is best addressed with EEx, relative rest and movement retraining. In fact, treatment recommendations for the management of PT are similar to AT. Appropriate loading of a diseased tendon with EEx, heavy slow resistance training and isometric exercises can improve pain and function in common tendinopathies of the Achilles and patellar tendons 5,7,9,12,16–23. In a recent review, Reinking summarizes the effectiveness of various modalities for the treatment of PT 9. In line with earlier research, Reinking stipulates performing EEx with ‘some pain or discomfort’ 7, e.g. tendon pain greater than 0 and less than 5 on a 0-10 pain scale for a single leg decline squat. A painful response is critical for improving pain and function in tendinopathies of the patellar tendon 8. He also discusses ‘eccentric decline squats’ vs standard squat training for treating PT. The rationale is that decline squats (on a 25 degree decline board) can increase patellar tendon load and quadriceps activation significantly more compared with standard squat. To date, there is not enough evidence base for choosing decline squats over standard squats for treating PT on outcomes such as pain, performance or return to sports.

Key takeaways

  • EEx are part of the first line treatment for improving pain and function in most common tendinopathies
  • A diseased tendon can be loaded with EEx, but also heavy slow resistance training and isometric exercises can improve pain and function
  • Loading of diseased tendons with EEx should (re-)produce tendon pain, but pain should not be progressive or disabling. As always: systematic clinical reasoning and incorporation of patient values to optimize outcomes are key
  • Treatment recommendations for Achilles and patellar tendinopathies are basically the same.

Author and Affiliations: 

By Michiel R.M. Twiss, @physiotwiss

Michiel R.M. Twiss is a Dutch physiotherapist in Buchs SG, Switzerland. He has a keen interest in systematic reviews and meta-analyses in gerontology research and specifically strength and conditioning training in old age. He holds a private practice in Buchs, Sankt Gallen, Switzerland.

References

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