Thank you to everyone who has taken the time to read my blog posts so far! The blog has received over 200 views in little over a week which is more than I could have hoped for! The third in my series of blogs follows on from a discussion point at this weeks @GoPerformUK Football Medicine evening (https://preventionphys.wordpress.com/2018/03/15/football-medicine-evening-a-reflection/) and will relate to the influence of the Nordic Hamstring Exercise on Biceps Femoris fascicle length.
Firstly before we discuss the effect of NHE on fascicle length it is important to understand why we would want to prescribe an exercise than can influence this architectural change, and even before that know what a fascicle actually is!
A muscle fascicle is a bundle of muscle fibres (Figure One) which is commonly measured in the research through use of ultrasound imaging. A change in fascicle length, suggests an “addition of sarcomeres in series within the muscle, which enables operating over a greater range of motion without overstretch” (Guex et al., 2016).
Figure One: Taken From https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025387/
To understand why we are looking to induce fascicle change we must refer to the great work of Timmins et al. (2016) who completed a strong prospective study in screening of potential risk factors to hamstring injury. After screening a number potential risk factors the authors found that the players who suffered from subsequent hamstring injury displayed significantly shorter fascicles compared to their uninjured limb and also the uninjured players two limb average. Figure Two demonstrates the significant effect that increased fascicle length at baseline screening appears to have on decreasing the risk of hamstring injury. Timmins et al. (2016) reported that for every 0.5cm increase in Long Head of Biceps Femoris fascicle length we can reduce the risk of hamstring injury by a staggering 73.9%.
Figure Two: Taken From Timmins et al. (2016).
With substantial decrease in injury risk with fascicle length change then we need to explore the literature surrounding NHE induced architectural changes. The first of these papers is a study published only this year by Alonso-Fernandez et al. (2018) who utilised a high volume NHE protocol over a nine week period. The study demonstrated a significantly greater fascicle length in participants following participation in the study (Figure Three). Also interestingly they reassessed architecture after 4 weeks of detraining and found a reversal of these effects, a topic which will feature in the final blog of this series surrounding how and when to prescribe the NHE.
Figure Three: Taken From Alonso-Fernandez et al. (2018).
These results appear to support the previous research of Bourne et al. (2017) who displayed a significant fascicle length increase in the NHE group versus the control group. The mean calculated increase in fascicle length was 2.2cm over the ten week intervention. If we remind ourselves of the Timmins et al. (2016) data proposing a 74% decrease in hamstring injury risk with 0.5cm increases, then this is obviously a very important and significant finding. For the balance of fairness it is also worth noting that the hip extension exercise completed by the third group in the study also displayed significant fascicle length increase, and also greater Biceps Femoris hypertrophy (Figure Four).
Figure Four; Taken From Bourne et al. (2017).
A study also completed last year by Seymore et al. (2017) found that fascicle length remained unaltered within a NHE group. They did however find that muscle volume increased following program completion. There was a few differences within the methodology of this study and that of the two previously discussed studies. This study was only six weeks in length, and therefore it would have been interesting to see if the study ran to nine or ten weeks as in the previous studies if they would have noticed fascicle length change. Also of note is that the cohort involved in the study. The groups were comprised of fourteen female particpants and six male participants. This is in contrast to the previous studies that utilised a male only cohort. This may therefore suggest that future research is needed to identify any difference in training adaptations between males and females.
This is the final blog in my series relating to arguments in favour of performing the NHE. For my next blog I will look to discuss the first argument against the NHE which is that it is a “non-functional” exercise.
As always please feel free to get in touch and voice your opinions on what has been discussed.
Alonso-Fernandez et al. (2018). Changes in muscle architecture of biceps femoris induced by eccentric strength training with Nordic hamstring exercise.
Bourne et al. (2017). Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: Implications for injury prevention.
Seymore et al. (2017). The effect of Nordic hamstring strength training on muscle architecture, stiffness, and strength.
Timmins et al. (2016). Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study.