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Strengthen to Lengthen

When we talk about strength training, what comes to mind? Perhaps an image of Arnold Schwarzenegger, with his large muscles and well-defined physique. But did you associate it with flexibility? Strength training has been recognised for so long as a way to improve the size and strength of our muscles. The concept that it can actually improve the length is relatively new.

I mentioned in the last post, how improving the stretch tolerance of a muscle can improve its resting and active length. This does not however change the properties of a muscle. The process for which a muscle increases in length is called sarcomerogenesis, through an addition of sarcomere in the series (Peviani et al 2018). Blazovich et al (2018) suggest that sarcomerogenesis is not a key factor in improving muscle length following stretching. This is due to the lack of increase in fascicle length observed in most human studies, or in sarcomere number in animal stretch models.

Let’s briefly recap the anatomy of a muscle. A muscle fibre consists of myofibrils. These are formed by a series of sarcomeres arranged in a longitudinal alignment. Within a sarcomere are thick filaments of myosin and thin filaments of actin. As a muscle contracts concentrically, the actin and myosin filaments overlap to shorten the sarcomere and create a force (Zollner et al 2012).

muscle fibre

(Openstax 2015)

Single muscle fibres are triggered to grow when they detect a mechanical load, through receptors in their cell membranes. In order for all the fibres in the muscle to grow, the muscle should be loaded through its full range. This would suggest why strength training may be perceived to reduce flexibility, as it is common for weightlifters to only work through the strongest part of their muscle which is the mid-range (Beardsley 2018).

During an eccentric contraction, some sarcomeres are stretched beyond myofilament overlap and become disrupted. This disruption grows with repeated contractions, leading to membrane damage (Rassier 2017). This is followed by protein synthesis and sarcomerogenesis in the process of repair. Sarcomerogenesis after eccentric exercise was evidenced by using laser light diffraction to measure sarcomere numbers, in the hind-limb muscles of rats (Brockett et al 2001).

The addition of sarcomeres in series allows muscle fibres to operate at longer lengths, as the muscle is stronger towards the end of its range. This is believed to decrease the potential for further muscle damage as the muscle can withstand greater loads. The result of this is a prolonged shift in the muscle length-tension curve in the direction of longer muscle lengths (O’Sullivan et al 2012).

length tension curve

(Black 2011)

It has been shown that sarcomerogenesis can occur within 10 days of starting eccentric training (Brockett et al 2001). This was performed as 12 sets of 6 repetitions of the Nordic hamstring exercise, however the exercise was only performed on day 1 and day 8. This raises the question for whether more regular training will result in an earlier response.

Mahieu et al (2008) also found that an eccentric training regime provided a significant increase in dorsiflexion range of motion after only 6 weeks. Within this study, the eccentric exercise was a heel drop, performed as 3xsets of 15 reps daily. This increase was accompanied by a decrease in the passive resistive torque, which is further evidence that structural changes occur after eccentric loading.

Both of these studies support the hypothesis that eccentric training can result in the lengthening of muscles. The systematic review by O’Sullivan et al (2012), involving 6 randomised control trials, provided strong evidence that eccentric training provides a significant increase in muscle length, rated as high quality on the pedro scale. The improvement observed was measured as a change in fascicle length as well as range of motion available at the muscle. Fascicle length and range of motion are both closely related to changes in the muscle length-tension curve, supporting the hypothesis that it improves flexibility (O’Sullivan et al 2012).

More recent studies have all arrived at the same conclusion. Abdel-aziem et al (2018) identified improvements in hamstring flexibility and eccentric peak torque following eccentric training. Interestingly, they also observed that the improvement was greater in untrained subjects than in trained. The eccentric intervention was performed for 6xsets of 5 repetitions, 5xper week over a period of 6 weeks in pain-free subjects.

A study of particular interest was the one performed by Muhamad and Muhammad (2018). Although it is another study in pain-free subjects, they observed the effects in overweight and obese females. This is more generalizable than a lot of the studies in athletes due to over 1/3 of the world’s population being overweight or above on the BMI scale (Hruby and Frank 2015). Again, flexibility significantly increased following eccentric training of hamstring muscles compared to a control group of no intervention after 8 weeks.

Photo from my media library of the nordic hamstring exercise.

As you may have noticed, a high proportion of the studies were performed using the hamstring muscle. This may be due to the relative importance of hamstring flexibility to activities of daily living and sports performance (American College of Sports Medicine 2018). They were also only performed in pain-free subjects which limits the generalisability, as the patients we treat are usually in pain.

Eccentric training has also been consistently shown to provide other benefits. It has been observed to reduce the risk of injury, reduce pain and improve strength, power and performance (Douglas et al 2017).

There was recently a period where eccentric loading had gained widespread implementation within the rehabilitation setting. It was widely used in the treatment of tendinopathy, with Alfredsons (1998) protocol being more of the well-known interventions.

More recently, the evidence has suggested that any form of loading appears as beneficial as another, whether it be concentric, eccentric or isometric (Bohm et al 2015). This still suggests that eccentrics have their part to play though, and with the added benefit of improving flexibility they could still provide a useful adjunct in rehab.

If eccentric training can significantly increase muscle length, as well as its other benefits, then do we still need to be performing stretches? Studies comparing the effectiveness of stretching with eccentric training for flexibility would therefore be of particular interest to determine this. One guess what the next post will be about…


Abdel-aziem, A et al (2018). Isokinetic peak torque and flexibility changes of the hamstring muscles after eccentric training: Trained versus untrained subjects. Acta orthopaedica et traumatological turcica, [online] 52 (4), pages 308-314. Available at [accessed 24th December 2019].

American College of Sports Medicine. ACSM’s guidelines for exercise testing and prescription. 10th ed. Philadelphia: Wolters Kluwer; 2018.

Alfredson, H et al (1998). Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Journal of Sports Medicine, [online] 26 (3), pages 360-366. Available at: [accessed 12th January 2020].

Beardsley, C (2018). What is muscle growth and how does it happen? [blog] medium. Available at: Last accessed 26th December 2019.

Blazevich, A (2018). Adaptations in the passive mechanical properties of skeletal muscle to altered patterns of use. Journal of applied Physiology, [online] 126 (5), pages 1483-1491. Available at: [accessed 2nd January 2020].

Bohm, S et al (2015). Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis of exercise intervention studies on healthy adults. Sports medicine – open, 1 (7).

Brockett, C et al (2001). Human hamstring muscles adapt to eccentric exercise by changing optimum length. Medicine and science in sports and exercise, 33 (5), pages 783-790.

Douglas, J et al (2017). Chronic adaptations to eccentric training: a systematic review. Sports medicine, [online] 47, pages 917-941. Available at: [accessed 1st January 2020].

Ferreira, D et al (2007). Analysis of the influence of static stretching and eccentric training on flexibility of hamstring muscles. International Symposium on Biomechanics in Sports, 25.

Hruby, A and Frank B (2015). The epidemiology of obesity: A big picture. Pharmacoeconomics, [online] 33 (7), pages 673-689. Available at [accessed 1st January 2020].

Lynn, R et al (1998). Differences in rat skeletal muscles after incline and decline running. Journal of applied Physiology, 85 (1), pages 98–104.

Mahieu, A et al (2008). Effect of eccentric training on the plantar flexor muscle-tendon tissue properties. Medicine and science in sports and exercise, 40 (1), pages 117-123.

Muhamad and Muhammad (2018). Effects of 8 weeks of eccentric training on hamstring flexibility and muscular performance among healthy overweight and obese women. International journal of public health and clinical sciences, [online] 5 (3), pages 192-203. Available at: [accessed 3rd January 2020].

O’Sullivan, K et al (2012). The effects of eccentric training on lower limb flexibility: a systematic review. British journal of sports medicine, [online] 46 (12), pages 838-845. Available at: [accessed 10th December 2019].

Peviani, S et al (2018). Regulation of extracellular matrix elements and sarcomerogenesis in response to different periods of passive stretching in the soleus muscle of rats. Scientific reports, 8 (9010).

Rassier, D (2017). Sarcomere mechanics in striated muscle: from molecules to sarcomeres to cells. American journal of physiology, 313 (2), pages 134-145.

Zollner, A et al (2012). Stretching skeletal muscle: chronic muscle lengthening through sarcomerogenesis. Plos one, [online] 7 (10). Available at: [accessed 1st January 2020].


Black, C (2011). The active length-tension curve. [online]. Accessed 2nd January 2020. Available at:

Madison Square Garden Centre (1974). Arnold Schwarzenegger before defending the title for his fifth Mr. Olympia contest in 1974. [online]. Accessed 2nd January 2020. Available at:

Openstax (2015). Muscle fibres. [online]. Accessed 2nd January 2020. Available at: Https://

Published by physiopete

Musculoskeletal outpatients Physiotherapist in primary care. Part-time academy physio at Sheffield Wednesday Football Club. Currently studying my MSc at Nottingham University part time.

7 thoughts on “Strengthen to Lengthen

    1. Based on the research, if we can achieve the same effects with eccentric exercises as we can with stretching, then because of the other added benefits to eccentric exercises we might not need to give stretches at all. This would save time and mean the patients have less exercises that they need to focus on. However, as mentioned in my flexibility post, there is not any evidence comparing using both together, with either one in isolation, which may provide faster results.

      Liked by 1 person

    1. Thankyou Laurence. Yes, since I have started to look into the evidence, my practice has most definitely changed. I would say that I used to prescribe stretches to more than half of my patients, whereas now this is minimal. This is due to my decreased perception of the importance of flexibility, as mentioned in my flexibility post, as well as the greater focus on eccentric loading. I have found that my patients have improved faster both with pain levels as well as functionally.

      Liked by 1 person

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