Welcome to the 7th edition of the Learn.Physio Research Review!

Isometric, Eccentric, Concentric, what's the best exercise for a tendon?

A research review by Learn.Physio

Welcome to Issue 7! In this issue we’ll take a side-step outside of my clinical comfort zone and I’ll travel south, away from the knee and the ACL, to the Achilles tendon and the plantar fascia!

Both mid-portion Achilles tendon pain and plantar fascia pain, are common clinical presentations to most clinicians; but I find that they are also some of the more trickier conditions to treat and manage.

They are both conditions that you literally can throw everything in your toolkit at (including the kitchen sink), and yet still the pain and dysfunction can linger in the patient.

There is so much in the literature about these 2 conditions to try and optimise their rehab, but today I want to hone in specifically at if there are active strengthening exercises that you could employ in your management strategy for both mid-portion Achilles tendon pain and plantar fascia pain.
I hope you enjoy this fortnight’s summaries and learn something new.


One in 10 people will be affected by plantar fascia pain (or plantar fasciopathy, plantar heel pain or “plantar fasciitis”) at some point in their lives. It is characterised by sharp heel pain, often most intense in the morning or after periods of inactivity. The pain often improves with movement, but it can worsen with extended periods of time on feet.
Resistance training is commonly prescribed for people with musculoskeletal pain; with early evidence suggesting that plantar fascia pain too can be treated effectively with high-load, isotonic strength training (Rathleff et al 2015).
Isometric exercises have also been found to be effective in reducing pain in athletes with patellar tendon or Achilles tendon pain (Rio et al 2015, Malliaras et al 2013 & Rowe et al 2012).
With such promise between the 2 forms of muscle contraction types on both short term outcomes (reduced pain), and long terms outcomes (improved function and quality of life), the aim of this trial was to determine if one was more effective than the other in reducing immediate pain in people with plantar fascia pain.
The authors compared isometric exercise, isotonic resistance exercise and walking and they hypothesised that isometric exercise would induce more analgesia immediately after exercise than isotonic exercise or walking.

This was a very well conducted, randomised cross-over clinical trial where participants were blinded to the hypothesis and did not know which exercise was hypothesised to reduce pain the most.
Inclusion criteria:

  • History of inferior heel pain for at least 3 months prior to enrolment in the trial
  • Pain on palpation of the medial calcaneal tubercle or the proximal plantar fascia
  • Thickness of the plantar fascia of 4.0mm or greater on ultrasound
  • Pain during at least one of the 3 pain aggravating activities (static stance, half squat and heel rise). These exercises were chosen as previous research indicated that 88% of participants would experience pain aggravation from at least 1 of these 3 exercises.
  • Mean heel pain of 20mm/100mm VAS (0mm = no pain, 100mm = worst pain imaginable) during the past week
Exclusion criteria:
  • Less than 18yrs of age
  • History of inflammatory systemic diseases
  • Pain or stiffness in the 1st MTPJ to an extent that exercises cannot be performed
  • Prior heel surgery
  • Pregnancy
  • Pain medication
  • Corticoid steroid injection into the plantar fascia within the last 6 months

Outcome measures:
The primary outcome measure for this trial was pain experienced during the pain-aggravating activity – with a 19mm reduction in pain on the VAS being considered to be the minimal important difference in this population.
To gather pain information, each of the participants performed the 3 single-leg pain aggravating exercises. After performing each exercise, they were asked to mark on a 100mm line their pain experience, with the line anchored left with “no pain”, and the end of the line anchored right with “worst pain imaginable”. The procedure for each aggravating exercise was as follows:

  1. Static single leg stance
    1. 30sec hold
    2. Participants allowed to stabilise themselves by placing a hand on the wall
  2. Half squat
    1. Participant flexed the knee to 45deg knee flexion
    2. Performed for 10 reps with a 1sec eccentric and 1sec concentric phase
  3. Single leg heel rise
    1. Participant performed a maximal plantar flexion with knee in full extension
    2. Performed 10 reps of 1sec eccentric and 1sec concentric phase
Secondary outcome measures included; thickness of the plantar fascia on ultrasound, pressure pain threshold on the most painful spot under the heel and pain during the exercise sessions.
After the completion of each exercise session, participants rated their average pain experienced during the session; with outcomes being evaluated in the same order before and after each session.
In regards to the interventions, participants attended 3 sessions (isometric, isotonic and walking) over the course of 2 weeks (with a minimum 48hr rest interval between sessions) with the order of the exercises randomised. The interventions are detailed below:
  • Isotonic:
    • Single leg heel rise performed with the forefoot on the edge of a step
    • The toes were maximally dorsi flexed by placing a towel underneath them. The participant was instructed to perform a heel raise to maximal plantar flexion in the ankle joint and afterwards to lower the heel to maximal dorsi flexion. Supporting oneself for balance by placing the hands on a wall or a rail was allowed. The contraction time was guided by a metronome
    • 8RM load (additional load to body weight added to backpack or holding heavy objects so no more than 8 reps per set could be performed).
    • 4 sets of 8 reps with 2mins rest in between each set
    • Tempo: 3 sec up, 2 sec hold, 3 sec down
  • Isometric:
    • Single leg heel rise performed with the forefoot on the edge of a step
    • The participant was instructed to stand still with the ankle joint in neutral and hold this position. Supporting oneself for balance by placing the hands on a wall or a rail was allowed.
    • Load determined by asking participant to find a heavy object that they would not be able to hold for longer than 1min.
    • 5 sets of 45sec holds with 2mins rest between sets
  • Walking:
    • Performed barefoot
    • Instructed to walk at a pace they would use when walking at home
    • Duration was 4mins which was the same of time spent performing isometric and isotonic exercises

20 people were included in this trial (18 females, mean age 48.9yrs, mean BMI 31.3). On average they had experienced plantar fascia pain for a mean 8.5 months and at baseline had mean 64mm/100mm pain on VAS (6.5/10 pain) in the past week.
In regards to the primary outcome measure of immediate pain relief during a pain-aggravating activity, there were no significant differences between the 3 interventions. You can see in the pre-post graph below that the bold lines connecting the stars are the mean changes in VAS score after the intervention. The only intervention that had an overall immediate decrease in pain was the isotonic intervention; but this change was small and less than the 19mm minimal clinical important difference.

There was also no significant interaction between the 3 interventions and the secondary outcome measures.
This was the first trial comparing the acute analgesic effect on active interventions in patients with plantar fascia pain – and contrary to the authors hypothesis, isometric exercise was not better than isotonic exercise or walking in reducing pain – and to be fair, nor were the other two interventions. The results did show however, a trend in reduced pain in the isotonic intervention group, but this change in pain was not clinically significant.
As you can see from the graph above, participants had a varied response to isometric exercise with the authors reporting that only 3 out of 20 had a clinically relevant reduction in pain for both isotonics and isometrics.
As mentioned above, isometrics have been previously shown to be effective in the immediate effect on pain in Achilles and patellar tendon athletes; with one trial showing that in a group of male volleyball players isometric exercises (5x45sec holds, 2mins rest in between sets), their pain reduced by 68mm/100mm VAS and lasted at least 45mins post intervention (Rio et al 2015).
A big difference between Rio et al’s subjects and this trial was that this trial had more participants, were mostly female participants, were much older and higher BMI scores. It has been shown that younger people have greater exercise-induced hypoalgesia (Naugle et al 2012), and males respond better to isometric exercise than females (Lemley et al 2015). These are possible reasons why the subjects in this trial did not respond to the interventions given.
This was a really interesting study, and it struck a chord with my biases towards active interventions over passive interventions – however the results of this study showed that these active interventions actually didn’t do much for the vast majority of the participants.
But I do wonder what the treatment effect of isometric vs isotonic vs walking would be if they were performed daily (or every other day) over at least 4 weeks. Would we see a difference between the 3 interventions?
So as a clinician, what do we do now to help our patient presenting to us in pain? People often seek our expert advice to help them reduce their pain, so a study in the future comparing active intervention (isotonic or isometric exercises) vs passive intervention (eg. ESWT or taping or orthoses) vs control group would be nice to see.
In the meantime though, what do you offer to help your patient manage their pain? Taping? Orthoses? Manual therapy? Patient education and reassurance that this will get better over time with high load strengthening exercises as described by Rathlef et al? This is where I find this condition to be quite challenging and I often struggle as a clinician.
Contrary to what has been found in the Achilles and patellar tendons, the results of this study on the immediate pain-relieving effect of isometric exercise on plantar fascia pain failed to show that it was superior to isotonic exercise or walking.
In fact, the results of this trial showed a slight mean increase in pain across all 20 participants following isometric exercise and walking, whereas a slight reduction in pain was observed in the isotonic group (not clinically meaningful though).
What this means is that we need to be careful about generalising the types on one intervention (eg. isometric exercise for pain relief) and applying it to another body part (eg. patellar tendon vs Achilles vs plantar fascia vs gluteal tendon vs rotator cuff vs wrist flexors/extensors).
As previous research has shown that not one particular type of contraction type is superior to another for lower limb tendinopathies (van Ark et al 2016 and Beyer et al 2015), I think that we don’t discount the role of isometrics at all and start abandoning them all together, but rather we add them to the physio toolkit to be applied with sound clinical reasoning to the person sitting right in front of us.
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Achilles tendinopathy (AT) is a common complaint characterised by local pain (usually to the mid-portion of the Achilles tendon), morning stiffness and reduced function, and accounts for 6-10% of running-related injuries in athletes.
A cornerstone to the management of AT is exercise-based rehabilitation, and it was shown in a recent meta-analysis of 24 studies that exercise-rehabilitation for at least 12 weeks can result in a significant (and clinically meaningful) 21-point improvement in VISA-A scores (Murphy et al, 2018). However, in the literature, there are as many as 6 different types of exercise interventions/protocols aimed at improving pain and function in patients with AT. These being:

  • Heavy eccentric calf training (Alfredson eccentric protocol) – Alfredson et al 1998
  • Modified Alfredson eccentric protocol (lower volume) – Stevens et al 2014
  • Concentric training – Mafi et al 2001
  • Eccentric overload training (Silbernagel protocol) – Silbernagel et al 2001
  • Heavy, slow resistance training – Beyer et al 2015
  • Stanish protocol – Stanish et al 1986

For many years, the Alfredson protocol was seen by many clinicians as the way to manage AT – however it hasn’t been systematically compared to natural history (wait and see approach), sham intervention or traditional physiotherapy groups.
The Alfredson protocol is also quite time consuming, in that the traditional protocol asks the patient to perform 180 repetitions each day (3x15 straight knee heel raises and 3x15 bent knee heel raises, 2x per day) for 12 weeks straight – which can be difficult to integrate into rehab plans when athletes are still trying to train, jump and run with no scheduled rest days. Considering that alternative protocols such as heavy, slow resistance training only requires between 18-60 repetitions, 3x per week, for 12 weeks, it would be beneficial for clinicians and patients to explore less time-consuming, yet equally effective treatment options for the management of AT.
The objective of this systematic review was to assess the effectiveness of heavy, eccentric calf training (HECT - Alfredson protocol) in comparison to natural history, traditional physiotherapy (deep friction massage, other forms of manual therapy, ultrasound and/or taping), sham interventions (interventions that were highly unlikely to result in a pathophysiological response which would influence pain and function) or other exercise interventions for improvements in pain and function in mid-portion AT.


Only randomised control trials and quasi-randomised trials were included in this meta-analysis if one study arm used HECT to treat mid-portion AT, and the other arm used a natural history, sham rehab, traditional physio or other exercise intervention.
Both physically active and sedentary participants were included that were aged at least 18 years of age and were identified to have mid-portion AT for at least 3 months. Studies that included insertion AT or other types of causes of heel pain were excluded.
Exercise interventions were included if they used either isometric, eccentric, concentric or isotonic interventions and the comparisons of interest were:

  • HECT vs natural history
  • HECT vs sham exercise
  • HECT vs traditional physiotherapy
  • HECT vs different exercise interventions

Studies were also only added if they used a valid and reliable outcome measure of pain and function in mid-portion AT – this being the VISA-A; which has been shown to be the only valid and reliable patient outcome measure published to date. Trials that only used pain scales such as VAS or NRS were not included.
The systematic review process kept in line with PRISMA guidelines for conducting a thorough systematic review and meta-analysis.

A total of 7 studies met the criteria and were included in these meta-analyses. This included 241 participants with a mean age ranging from 36-49 years of age, with females accounting for 54% of the participants. Regarding length of time, they had symptoms and the severity of symptoms; the mean time frame of symptoms ranged from 6 – 28 months, and all were deemed to have a moderate level of disability due to their mid-portion AT pain (mean VISA-A scores ranged from 36-62 points, with a score of 90% being considered recovered from AT – Iversen et al 2012).
The effect of the interventions is as follows:

  • One study compared HECT to natural history.
    • The one and only study conducted showed a statistically significant change in VISA-A scores in in favour of HECT over natural history.
    • The quality of this RCT was low however, and research compared to placebo would be needed in the future to state the true effect of HECT compared to natural history.
  • No studies compared HECT to sham exercise intervention.
  • Two studies compared HECT to traditional physiotherapy.
    • The results of these 2 studies were pooled and the was a significant effect in favour of HECT over traditional physiotherapy.
    • Once again, the quality of the RCTs were deemed to be low, and authors unable to state the true effect of HECT over traditional physiotherapy.
  • Four different studies compared HECT to other exercise interventions.
    • Four studies were pooled and there was a non-significant effect between any of the exercise interventions.
    • Note: one of the 4 papers was identified as a high risk of bias and once excluded from the data-analysis, the results changed from no between group differences to a significant result in favour of other forms of exercise interventions over HECT. The significant difference however was still lower than the minimal clinical important difference of at least 10 points of VISA-A.

These findings of this systematic review highlight 3 key areas of management of the patient presenting with mid-portion AT.
Firstly, active exercise rehabilitation is superior to a wait-and-see / natural history (ie. AT will get better on its own). I think intuitively as clinicians, we all knew that, but it is an important thing to discuss that some patients may experience an improvement in their symptoms with rest and avoiding aggravating activity, but it is very common (in my clinical experience anyway), that their mid-portion AT pain resumes shortly after they return to their previous aggravating activities (eg, running, hopping).
So, I would sure to add in a thorough and progressive overload rehab plan during periods of avoiding aggravating exercises to minimise the chances of seeing a recurrence later. The updated review of the continuum model of tendon pathology by Cook et al (2016) is a must-read for all clinicians. Full text link to this paper
Secondly, it appears that “traditional” treatment options such as manual therapy, massage, ultrasound, and taping are not as effective at managing mid-portion AT pain when compared to HECT alone. The quality of evidence here though was low, so it is hard for clinicians to know the true positive effect of HECT over traditional physiotherapy treatment options.
The big take away for me however was the conflicting results for what active exercise options were effective in managing patients with mid-portion AT. Even if there is conjecture here, what it does mean that even if HECT is equally effective as other forms of exercise options for mid-portion AT patients, it means that we have more choice on what we prescribe to our patients, knowing that we are going to have a positive impact on their pain and function.
For example, it was highlighted above that the “traditional” Alfredson’s protocol is to be performed 2x per day (180 reps per day) for 12 weeks straight, to have a positive effect on outcomes. To many patients, this program is hard to adhere to; especially when they have busy lives and have congested training schedules and need to account for rest and recovery. Whereas the heavy, slow resistance training program from Beyer et al was programmed at 18-60 reps per exercise (3 exercises), per session (3x per week) for 12 weeks; and would be much realistic to complete for most patients and athletes and allows for rest/recovery days so that other training can be incorporated safely into the training week.
Conversely, the advantage of doing the “traditional” Alfredson’s protocol is that it is easily completed at home (+/- a backpack with extra weight if required), whereas the heavy, slow resistance training of Beyer et al requires heavy loads and gym machines such as a smith machine (Gastrocnemius strengthening), seated calf raises (soleus strengthening) and leg press (proximal strengthening of quads and glutes) to complete the program.
Interestingly, the subjects conducting the heavy, slow resistance program of Beyer et al showed equal outcomes to the Alfredson’s protocol by completing all the exercises with 2 legs at a time (eg. Double leg standing heel raises, double leg seated heel raises, double leg leg press) compared to the Alfredson’s protocol that focuses on training just the affected leg only. I wonder if there would be any superior differences seen in these results from Beyer if they completed the heavy, slow resistance training with just the effected leg only?
In summary, despite some limitations to the current quality of RCTs in the literature, clinicians can be confident in giving at least 12 weeks of rehabilitation exercises aimed at addressing calf strength (and proximal musculature) in patients with mid-portion AT. Which type of program you give however really depends on the patient sitting in front of you and what they are most likely able to complete and adhere to. In regard to using “traditional” physiotherapy interventions in conjunction with exercise rehabilitation for the management of mid-portion AT, the choice is yours, and once again depends on the patient sitting in front in terms of their beliefs on what can help them manage their pain/improve their function and meeting their expectations.

In reality whilst it is nice to have a receipe treatment format of isometric into eccentric then concentric, nothing replaces the person in front of you.

The concepts of why or when you should use these exercises become far more important in clinical settings. 

Learn these concepts today in Ebonie Rio & Sue Mayes's Masterclass, The Athletic Ankle

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Rathleff MS, Mølgaard CM, Fredberg U, Kaalund S, Andersen KB, Jensen TT, Aaskov S, Olesen JL. High-load strength training improves outcome in patients with plantar fasciitis: A randomized controlled trial with 12-month follow-up. Scand J Med Sci Sports. 2015 Jun;25(3):e292-300. doi: 10.1111/sms.12313. Epub 2014 Aug 21. PMID: 25145882.
Rio E, Kidgell D, Purdam C, Gaida J, Moseley GL, Pearce AJ, Cook J. Isometric exercise induces analgesia and reduces inhibition in patellar tendinopathy. Br J Sports Med. 2015 Oct;49(19):1277-83. doi: 10.1136/bjsports-2014-094386. Epub 2015 May 15. PMID: 25979840.
Malliaras P, Barton CJ, Reeves ND, Langberg H. Achilles and patellar tendinopathy loading programmes : a systematic review comparing clinical outcomes and identifying potential mechanisms for effectiveness. Sports Med. 2013 Apr;43(4):267-86. doi: 10.1007/s40279-013-0019-z. PMID: 23494258.
Rowe V, Hemmings S, Barton C, Malliaras P, Maffulli N, Morrissey D. Conservative management of midportion Achilles tendinopathy: a mixed methods study, integrating systematic review and clinical reasoning. Sports Med. 2012 Nov 1;42(11):941-67. doi: 10.1007/BF03262305. PMID: 23006143.
van Ark M, Cook JL, Docking SI, Zwerver J, Gaida JE, van den Akker-Scheek I, et al. Do isometric and isotonic exercise programs reduce pain in athletes with patellar tendinopathy inseason? A randomised clinical trial. J Sci Med Sport. 2016 Sep;19(9):702–6
Beyer R, Kongsgaard M, Hougs Kjær B, Øhlenschlæger T, Kjær M, Magnusson SP. Heavy slow resistance versus eccentric training as treatment for achilles tendinopathy: A randomized controlled trial. Am J Sports Med. 2015 Jul;43(7):1704–11.
Murphy M, Travers M, Gibson W, Chivers P, Debenham J, Docking S, Rio E. Rate of Improvement of Pain and Function in Mid-Portion Achilles Tendinopathy with Loading Protocols: A Systematic Review and Longitudinal Meta-Analysis. Sports Med. 2018 Aug;48(8):1875-1891. doi: 10.1007/s40279-018-0932-2. PMID: 29766442.
Alfredson H, Pietilä T, Jonsson P, Lorentzon R. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med. 1998 May-Jun;26(3):360-6. doi: 10.1177/03635465980260030301. PMID: 9617396.
Stevens M, Tan CW. Effectiveness of the Alfredson protocol compared with a lower repetition-volume protocol for midportion Achilles tendinopathy: a randomized controlled trial. J Orthop Sports Phys Ther. 2014 Feb;44(2):59-67. doi: 10.2519/jospt.2014.4720. Epub 2013 Nov 21. PMID: 24261927.
Mafi N, Lorentzon R, Alfredson H. Superior short-term results with eccentric calf muscle training compared to concentric training in a randomized prospective multicenter study on patients with chronic Achilles tendinosis. Knee Surg Sports Traumatol Arthrosc. 2001;9(1):42-7. doi: 10.1007/s001670000148. PMID: 11269583.
Silbernagel KG, Thomeé R, Thomeé P, Karlsson J. Eccentric overload training for patients with chronic Achilles tendon pain--a randomised controlled study with reliability testing of the evaluation methods. Scand J Med Sci Sports. 2001 Aug;11(4):197-206. doi: 10.1034/j.1600-0838.2001.110402.x. PMID: 11476424.
Stanish WD, Rubinovich RM, Curwin S. Eccentric exercise in chronic tendinitis. Clin Orthop Relat Res. 1986 Jul;(208):65-8. PMID: 3720143.
Iversen, J. V., Bartels, E. M., & Langberg, H. (2012). The victorian institute of sports assessment - achilles questionnaire (visa-a) - a reliable tool for measuring achilles tendinopathy. International journal of sports physical therapy7(1), 76–84.
Cook JL, Rio E, Purdam CR, Docking SI. Revisiting the continuum model of tendon pathology: what is its merit in clinical practice and research? Br J Sports Med. 2016 Oct;50(19):1187-91. doi: 10.1136/bjsports-2015-095422. Epub 2016 Apr 28. PMID: 27127294; PMCID: PMC5118437.

Thanks for reading and staying up to date. I look forward to sharing more in the future.

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