Hamstring muscles activation: implications for strategies to prevent hamstring injury & treatment
Impact of exercise selection on hamstring muscle activation.
Bourne MN1,2,3, Williams MD4, Opar DA5, Al Najjar A6, Kerr GK1,2, Shield AJ1,2.
Review:
The authors did Hamstring muscles activity using nEMG, during ten common exercises. Additionally, they compared two of these exercise hamstring using fMRI. First, the authors recruited a sample size that was sufficient to show statistical significance. He also demonstrate a 10% difference in ratio between the biceps femoris (BF) to the medial hamstrings (MH). The authors selected a variety of commonly used open- and closed-chain hamstring exercises. Third, the figures utilized to present data allowed the reader to easily identify nEMG levels of specific exercises and make comparisons of the BF to the MH activation ratio.
Before application to practice limitation to this study should be address. First, the reference maximal voluntary isometric contraction (MVIC) may not represent a “true max” (although may still serve as a reasonable reference marker), as can be seen in the nEMG levels of several exercises reaching levels of activation beyond 100%.The MVIC the subjects were positioned in prone position with resistance at their ankles, creating a significant moment arm on a muscle already shortened at its proximal attachment
Second, the reference electrode used during the nEMG readings. It was placed on the fibular head where the biceps femoris has insertion . Although the BF is likely tendon, with little or no contractile tissue, the electrode could have been placed in an area less likely to pick-up interference – for example, the bony tibial crest. Last, the exercises selected for fMRI were based on results from the nEMG data; however, consideration of the most commonly used exercises may have resulted in a 3rd and potentially 4th exercise. However, all the exercises used in this study are common as to be found in almost every routine across a wide variety of settings.
Why is this study important?
Understanding hamstring activation patterns of various exercises may be used to optimize exercise selection. This includes reducing or eliminating exercises that may reinforce compensation patterns, eliminating exercises that place excessive load on a muscle at risk for further injury, or adding exercises that may preferentially recruit commonly under-active muscles. Relative to this study, the commonly becomes synergistically dominant relative to an inhibited gluteus maximus . Reducing the amount of exercise that preferentially recruits the biceps femoris is likely beneficial for optimizing motion and reducing the risk of future injury.
How does it affect practice?
From the the study it demonstrate that the lunge and 45° hip extension exercise have a greater concentric BF/MH ratio which is compared to the leg curl and bent knee bridge exercise. This may imply that the lunge and 45° hip extension exercise (commonly used for “back strengthening”) should not be part of the initial phases of a rehabilitation program post hamstring injury. Further, the 45° hip extension exercise had a greater eccentric BF/MH ratio as compared to the Nordic curl, bent knee bridge, leg curl and glute ham raise. It implies that that the 45° hip extension exercise may be a poor choice of exercise.
In general, compound movement had better BF/MH ratios (lunges, deadlifts, swings, single leg deadlifts, bridges)
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