by Bret Contreras March 28, 2017
The S&C Research review service comes out on the first day of every month. Here is a preview of the April 2017 edition, which comes out on Saturday. Each edition covers a wide range of exciting new research but this edition has a special theme of Hamstring Strains! Not included in this preview edition is Mendiguchia’s paper on hamstring rehab because it was covered in THIS interview which was posted a few days ago.
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The study: Schuermans, J., Danneels, L., Van Tiggelen, D., Palmans, T., & Witvrouw, E. (2017). Proximal Neuromuscular Control Protects Against Hamstring Injuries in Male Soccer Players: A Prospective Study With Electromyography Time-Series Analysis During Maximal Sprinting. The American Journal of Sports Medicine.
The researchers measured the muscle activation of the hip and trunk muscles in the acceleration phase of sprint running, in order to assess whether it is related to the risk of incurring a hamstring strain injury, in amateur soccer players. Therefore, they measured the muscle activation of the external and internal obliques, thoracic erector spinae, lumbar erector spinae, gluteus maximus, medial hamstrings, and biceps femoris (bilaterally) in the front swing, stance, and backswing phases of gait during a 40m linear sprint on a running track, and then measured injuries over the subsequent 1.5 seasons.
The researchers found that non-injured athletes displayed higher gluteus maximus EMG amplitudes in the front swing phase, and higher trunk muscle EMG amplitudes in the backswing phase of the sprinting test. Receiver operating characteristic (ROC) curve analysis was performed to identify the cut-off points that were the best predictors of HSI. ROC curve analysis showed that gluteus maximus EMG amplitude in the initial part of the front swing phase was able to predict HSI with a sensitivity of 82% and a specificity of 74%, with a cut-off value at 145% of normalized EMG amplitude. In comparison with many other previous injury prediction tests, this is a very high score. In addition, ROC curve analysis showed that trunk muscle EMG amplitude in the terminal part of the backswing phase was able to predict HSI with a sensitivity of 60% and a specificity of 68%, with a cut-off value at 90% of normalized EMG amplitude.
The researchers concluded that higher levels of gluteus maximus and trunk muscle activation in the flight phases of sprinting were prospectively associated with a lower risk of hamstring injuries during subsequent follow-up.
The study: Sugiura, Y., Sakuma, K., Sakuraba, K., & Sato, Y. (2017). Prevention of hamstring injuries in collegiate sprinters. Orthopaedic Journal of Sports Medicine, 5(1).
The researchers performed a retrospective analysis to compare the incidence of hamstring strain injury in 613 collegiate male sprinters over 24 years over 3 consecutive periods of time, in which different injury prevention methods were used. An incident of hamstring strain injury was defined as one that occurred during supra-maximal running training, and which led to >1 week without training or competition. The injury prevention program changed over the 24 seasons. Between 1988 – 1991 (period 1), the program involved only strength training; between 1992 – 1999 (period 2), the program involved both strength training and agility training; between 2000 – 2011 (period 3), the program involved strength training, agility training, and also added eccentric strength training (using the Nordic curl) and dynamic stretching. However, the sprint running training program did not change very substantially over the same period of time.
The incidence of hamstring strain injury during supramaximal running training per athlete-periods was 137.9 for period 1, 60.6 for period 2, and 6.7 for period 3, indicating a very substantial reduction in injury incidence over the 24 seasons.
The researchers concluded that the incidence of hamstring strain injury in track sprinters decreased over the successive 3 periods of time, during which (1) agility, and then (2) eccentric hamstring strength training and dynamic stretching were added to the injury prevention program.
The study: Seymore, K. D., Domire, Z. J., DeVita, P., Rider, P. M., & Kulas, A. S. (2017). The effect of Nordic hamstring strength training on muscle architecture, stiffness, and strength. European Journal of Applied Physiology, 1-11.
The researchers assessed the effects of long-term eccentric strength training using the Nordic hamstring curl on changes in muscle architecture, stiffness, knee flexion strength, and knee flexion angle of peak torque (APT), in recreationally active subjects. Subjects in the training group trained for 6 weeks using only the Nordic hamstring curl exercise in each workout. In addition, at each workout, both of the training and control groups performed 3 sets of static hamstring stretches (standing, seated, and supine), 6 times on each leg, for 30s per stretch.
Nordic hamstring curl strength training produced only non-significant increases in fascicle length and pennation angle (1.23% and 9.56%, respectively) but the increases in muscle volume and physiological cross-sectional area were significant (10.45% and 12.25%, respectively). Shear modulus (passive stiffness), passive knee flexion torque, and both eccentric knee flexion torque and APT measured by the dynamometer did not change.
The researchers concluded that the primary adaptation occurring within the biceps femoris (long head) after strength training using the Nordic hamstring curl was an increase in muscle volume.
The study: Alonso-Fernandez, D., Docampo-Blanco, P., & Martinez-Fernandez, J. (2017). Changes in muscle architecture of Biceps Femoris induced by eccentric strength training with Nordic Hamstring Exercise.
The researchers assessed the effects of long-term eccentric strength training with the Nordic hamstring curl, and of a subsequent detraining period, on the changes in muscle architecture, in recreationally active males. All subjects performed 8 weeks of eccentric strength training with the Nordic hamstring curl, followed by 4 weeks of detraining.
After training, muscle fascicle length increased by 23.9%, muscle thickness increased by 7.7%, and pennation angle decreased by 14.8%. After the detraining period, muscle fascicle length then decreased by 12.1%, muscle thickness decreased by 6.6%, and pennation angle increased by 9.2%. All changes were significant.
The researchers concluded that an 8-week period of eccentric strength training with the Nordic hamstring curl increases muscle fascicle length, increases muscle thickness, and decreases pennation angle. However, a detraining period of only 4 weeks reverses a large proportion of these adaptations.
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