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).
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).
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.
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…
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Beardsley, C (2018). What is muscle growth and how does it happen? [blog] medium. Available at: https://medium.com/@SandCResearch/what-is-muscle-growth-and-how-does-it-happen-b7f7cd68ee34. 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: https://www.ncbi.nlm.nih.gov/pubmed/30412028 [accessed 2nd January 2020].
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7 thoughts on “Strengthen to Lengthen”
It makes a lot of sense.
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Great post. I think both eccentric and stretching exercises should be combined in the treatment protocol.
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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.
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yes , I totally agree with you
Very much enjoyed reading your blog series Pete. Since creating the blog series has the strengthen to lengthen approach something you’ve made much success with in clinical practice with your patients?
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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.
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Love it Pete! Keep up the good work