Research Review By Dr. Shawn Thistle©

Date Posted:

June 2010

Study Title:

Eccentric exercises; why do they work, what are the problems and how can we improve them?

Authors:

Rees JD, Wolman RL, Wilson A

Author's Affiliations:

Defence Medical Rehabilitation Center, Surrey, UK; Department of Sport and Exercise Medicine, The Royal National Orthopaedic Hospital, London, UK.

Publication Information:

British Journal of Sports Medicine 2009; 43: 242-246.

Background Information:

In sports medicine, there are few injuries encountered more frequently than tendinopathies. Common sites for this often disabling condition are the Achilles, patellar, rotator cuff, wrist extensor group, adductor group and hamstring tendons. The exact pathology of tendinopathy is still under study, but it is now generally accepted that a degenerative process predominates, characterized by soft tissue remodeling resulting from a failed healing response (that is, the strain or demands imposed on the tendon exceed its healing capacity).

Absent from our current understanding of this condition is a significant inflammatory contribution, which explains the general lack of efficacy of common anti-inflammatory measures for treating these patients (as well as the shift in nomenclature from “tendinitis” to “tendinopathy or tendinosis”).

In the last 20+ years, eccentric (ECC) exercise has emerged as a popular treatment approach for a variety of tendinopathies. ECC exercises involve lengthening a muscle/tendon unit under load (versus concentric exercise which involves a shortening contraction or isometric which involves static holds). The literature to date, although criticized by some, points to the efficacy of ECC exercise for treating tendinopathies, particularly of the Achilles and patellar tendons.

Making generalized recommendations for other anatomical sites is difficult at this time due to the quality of published studies. Most utilize small sample sizes and have other drawbacks, but taken together a promising picture emerges while pointing to the need for further research.

Issues Surrounding ECC Exercise:

Tendon insertion (enthesis) vs. tendon body:

What has become evident based on existing literature is that different areas of tendons may respond differently to ECC exercise. Using the Achilles as a specific example, published trials demonstrate the effectiveness of ECC exercise for the tendon “body” (1), but not for insertional conditions (where the area of tenderness is at the enthesis) (2). Studies performed on patellar tendinopathy patients have not been consistent in their inclusion criteria to allow a similar comparison of efficacy.

Why do they work?

There are many proposed reasons why ECC exercises are effective. Originally it was suggested that ECC exercise produces greater force through the tendon that concentric exercise, and hence a greater remodeling stimulus (3). This may work by providing an adequate mechanical stimulus to “awaken” quiescent tendon cells. The same authors further suggested that since ECC exercises lengthen the muscle-tendon unit, that less force as actually being applied to the tendon itself during the motion.

Others have added that ECC exercise may increase tendon stiffness (4), increase collagen synthesis within the tendon (5) or provide a stimulus to re-vascularize the tendon secondary to the brief blood flow interruption that occurs during the performance of ECC exercises (6).

Early ECC protocols employed heavy loads, but recent work (7) has created controversy regarding the importance of overall load. This study actually showed that tendon loads are similar in ECC and concentric exercises. They also identified a fluctuating (sinusoidal) loading pattern during ECC exercise performance, which itself may provide a beneficial stimulus for healing (this of course cannot be stated with confidence until studied further).

Is ECC exercise a stretching or strengthening stimulus?

Another recent study (8) examined this question using the literature on Achilles tendons. The authors argue that despite receiving the label of a “strengthening” program, most ECC exercise protocols do not utilize common parameters of strengthening programs (such as ECC-concentric coupling with stretch-shortening etc.) and hence may be better described as specific “stretching” program.

They state that ECC motions often bring a tendon near its end range (while most concentric exercises do not), which may impart a unique stimulus to the tendons that assists healing. This stimulus may involve:
  • unique effects on the neurological reflex feedback loops
  • specific stimuli targeted to the passive components of the muscle-tendon unit (for example, fascia)
  • increased shear force between the tendon and paratendon (which may affect vascularity as proposed above)
  • de-sensitization to pain

Clinical Application & Conclusions:

ECC exercise certainly represents a viable treatment option for tendinopathy cases, particularly when involving the Achilles (especially chronic mid-tendon cases) and patellar tendons. However, the existing literature cannot specify a specific protocol for us to use for all tendinopathies. Published trials showing positive results of ECC exercise typically employ high repetitions (sets of 12-15) using heavier loads (starting with body weight and subsequently adding weight as need), repeated 1-2 times per day.

In other words, these programs impart a large stimulus to the tendon and attempt to overload it in a safe yet aggressive manner. Those who originally proposed this treatment stated that patients should perform these exercises even through pain, although this concept remains controversial today.

Prudent clinicians who employ ECC exercise with their patients should progress their patients accordingly and monitor compliance, results, and potential adverse reactions carefully. These programs can be challenging and may require extra attention from the supervising doctor or other clinic staff.

Additional References:

  1. Mafi N, Lorentzon R, Alfredson H. Superior short-term results with eccentric calf training compared to concentric training in a randomized prospective multicenter study on patients with chronic Achilles tendinosis. Knee Surg Sports Traumatol Arthroscop 2001; 9: 42-47.
  2. Fahlstrom M, Jonsson P, Lorentzon R et al. Chronic Achilles tendon pain treated with eccentric calf muscle training. Knee Surg Sports Traumatol Arthroscop 2003; 11: 327-333.
  3. Stanish WD, Rubinovich RM, Curwin S. Eccentric exercise in chronic tendinitis. Clin Orthop Rel Res 1986; 208: 65-68.
  4. Pousson M, van Hoecke J, Goubel F. Changes in elastic characteristics of muscle induced by eccentric exercise. J Biomech 1990; 23: 343-348.
  5. Landberg H, Rosendal L, Kjaer M. Training-induced changes in peritendinous Type I collagen turnover determined by microdialysis in humans. J Physiol 2001; 534: 297-302.
  6. Alfredson H, Pietila T, Jonsson P et al. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med 1998; 26: 360-366.
  7. Rees JD, Lichtwark GA, Wolman RL et al. The mechanism for efficacy for eccentric loading in Achilles tendon injury; an in vivo study in humans. Rheumatology 2008; 42: 746-749. Allison GT, Purdham C. Eccentric loading for Achilles tendinopathy – strengthening or stretching? Br J Sports Med 2009; 43: 276-279.