Understanding Hamstrings: Muscle Activity, Exercise And Prevention

As some of you may be aware we are hosting a Hamstring Seminar at the start of next month, and in preparation we are catching up on some of the latest research surrounding this topic. It can be an extremely confusing area as much has been done in the past 10 years, however people are still unsure of how to properly manage this injury. We are trying to get some of the best clinicians and researchers to give us an insight into their methods of assessment and management of some of the most complex topics. They will try to give us the most up to date research that they are using on their patients, hopefully helping us to stay up to date with best methods and practices.

 

So I would encourage everyone to have a read of the following few articles that have come out recently and consider how they may influence practice

 

 

  1. Hansen et al. Peak medial (but not lateral) hamstring activity is significantly lower during stance phase of running. An EMG investigation using a reduced gravity treadmill. Gait & Posture. (2017). 57 (7-10).

 

  • They discovered that increased hamstring muscle activation occurs with increased speed
  • The pre heel strike (swing phase) muscle activity peaks are higher than the post heel strike (stance phase) peaks for both the medial and lateral hamstrings.
  • The peak activation for both phases was slightly (but not statistically significantly) higher for the lateral hamstrings throughout the gait cycle whereas the medial hamstring peak was approximately 20% lower during stance (large effect size).
  • The reduction in peak activity of the medial hamstrings during swing phase suggests that there could be a relatively higher load being borne during running by the lateral hamstrings as the medial hamstrings are effectively afforded a slight “rest” during the swing phase.

 

We know that Nordics preferentially target the semitendinosus muscle (still has a large effect on muscle activation of the  BFlh). Maybe the role in Nordics is by increasing the load capacity of the semitendinosus?

 

 

  1.   Bourne et al. Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention. BJSM. (2016). 0 (1-9).

 

  • This study compared a 10 week programme between Hip Extension at 45 degrees, Nordic Hamstring Exercise and a control on measures of Bicep Femoris Fascicle length, muscle volume, architectural cross-sectional area (ACSA) and strength.
  • Some of the main findings:
    • BFLH volume increased significantly more in the HE than the NHE, however no significant changes were noted between the NHE and HE on semitendinosus muscle volume
    • The percentage change in BFLH ACSA was greater in the HE training group than in the NHE.
    • Participants increased their fascicle lengths from ∼10.6 cm prior to training, to 12.8 and 12.0 cm in the NHE and HE groups, respectively, which would likely result in large reductions in hamstring injury risk.
    • This study shows, for the first time, that the limited excursion of the hamstrings during the NHE does not prevent the exercise from increasing BFLH fascicle length. Indeed, the exercise resulted in greater fascicle lengthening than the HE, although the current study lacked the statistical power to distinguish between the two.  
    • Both exercises resulted in significant strength increases, which were similarly evident in the NHE and HE strength tests.

 

This study expands our understanding of other exercises often used in the rehabilitation and performance setting. The next step would be to do an RCT looking at the ability of the HE exercises to reduce Hamstring injuries across a season.

 

 

  1. Lovell et al. Hamstring Injury Prevention in Soccer: Before or After Training?. Scand J Med Sci Sports. (2017). Ahead of Print Online.

 

  • This article is an essential read if you are working in team sports whether as a Physiotherapist or Strength & Conditioning professional. It’s always a worry to carry them out before training, however post training fatigue may reduce the quality and compliance rates.
  • Three groups underwent a 12 week program, before training NHE group, after training NHE group and a core stability group.
  • The main findings from the study:
    • Changes in eccentric hamstring peak torque were greater in both NHEBEF (+11.9%; 3.6% to 20.9%) and NHEAFT (+11.6%; 2.6% to 21.5%) versus control (likely moderate effect), with no difference denoted between NHEBEF and NHEAFT .
    • The estimated change in biceps femoris fascicle length (expressed in both absolute, and relative to muscle thickness terms) was higher in NHEBEF versus both NHEAFT and CON.
    • Strength adaptation in the NHEBEF group was characterized only by an increased BF fascicle lengthening, whereas the NHEAFT cohort demonstrated the typical hypertrophic response, identified by an increased muscle thickness and pennation angle.
    • explained by the increased fascicle length that was exclusive to NHEBEF, the magnitude of which (12.9%) exceeded the minimum detectable change thresholds previously reported.
    • This study has demonstrated that scheduling Nordic hamstring exercises before or after football training has similar eccentric strengthening outcomes, but divergent architectural adaptations.

 

We know from some of the work done by David Opar and Dr. Anthony Shield group in Australia that the main protective mechanisms from Hamstring injuries is high eccentric strength and long fascicle length. The architectural adaptations for the NHE before group may be more advantageous however these may need to be explored in more detail over a longer period of time.

 

Let us know your thoughts!

 

Thomas Divilly

MSc MISCP CSCS