Hamstring Architectural and Functional Adaptations Following Long vs. Short Muscle Length Eccentric Training.

Kenny Guex,Cynthia Morisod,Francis Degache,Matthieu Sailly,Gregoire P Millet

doi:10.3389/fphys.2016.00340

Abstract

Most common preventive eccentric-based exercises, such as Nordic hamstring do not include any hip flexion. So, the elongation stress reached is lower than during the late swing phase of sprinting. The aim of this study was to assess the evolution of hamstring architectural (fascicle length and pennation angle) and functional (concentric and eccentric optimum angles and concentric and eccentric peak torques) parameters following a 3-week eccentric resistance program performed at long (LML) vs. short muscle length (SML). Both groups performed eight sessions of 3–5 × 8 slow maximal eccentric knee extensions on an isokinetic dynamometer: the SML group at 0° and the LML group at 80° of hip flexion. Architectural parameters were measured using ultrasound imaging and functional parameters using the isokinetic dynamometer. The fascicle length increased by 4.9% (p < 0.01, medium effect size) in the SML and by 9.3% (p < 0.001, large effect size) in the LML group. The pennation angle did not change (p = 0.83) in the SML and tended to decrease by 0.7° (p = 0.09, small effect size) in the LML group. The concentric optimum angle tended to decrease by 8.8° (p = 0.09, medium effect size) in the SML and by 17.3° (p < 0.01, large effect size) in the LML group. The eccentric optimum angle did not change (p = 0.19, small effect size) in the SML and tended to decrease by 10.7° (p = 0.06, medium effect size) in the LML group. The concentric peak torque did not change in the SML (p = 0.37) and the LML (p = 0.23) groups, whereas eccentric peak torque increased by 12.9% (p < 0.01, small effect size) and 17.9% (p < 0.001, small effect size) in the SML and the LML group, respectively. No group-by-time interaction was found for any parameters. A correlation was found between the training-induced change in fascicle length and the change in concentric optimum angle (r = −0.57, p < 0.01). These results suggest that performing eccentric exercises lead to several architectural and functional adaptations. However, further investigations are required to confirm the hypothesis that performing eccentric exercises at LML may lead to greater adaptations than a similar training performed at SML.

Highlights

Hamstring strain injuries, and especially biceps femoris long head strain injuries, are among the most frequent injuries in sports requiring high-speed running, such as football, rugby, Australian football, Gaelic football, American football, or track and field (Brooks et al, 2005; Ekstrand et al, 2011; Elliott et al, 2011; Alonso et al, 2012; Murphy et al, 2012; Orchard et al, 2013)
The aim of this study was to assess the changes in hamstring architectural and functional parameters following a 3-week eccentric resistance training performed at LML vs. short muscle length (SML)
In line with our hypothesis, the fascicle length (FL) and the eccentric peak torque at 30◦/s (EccPT) significantly increased in both groups, the ConOA significantly decreased in the LML group and tended to decrease in the SML group, while the EccOA tended to decreased in the LML group

Summary

Introduction

Especially biceps femoris long head strain injuries, are among the most frequent injuries in sports requiring high-speed running, such as football, rugby, Australian football, Gaelic football, American football, or track and field (Brooks et al, 2005; Ekstrand et al, 2011; Elliott et al, 2011; Alonso et al, 2012; Murphy et al, 2012; Orchard et al, 2013). Eccentric-based intervention has been shown to be a promising method to reduce the risk of hamstring strain injuries (Askling et al, 2003; Brooks et al, 2006; Gabbe et al, 2006; Arnason et al, 2008; Petersen et al, 2011; Nichols, 2013) This may be explained by the increase in eccentric strength and by the observed shift of the optimum angle (i.e., the angle at which peak torque occurs) in the direction of longer muscle length following an eccentric strength program (Brockett et al, 2001; Askling et al, 2003; Mjolsnes et al, 2004; Clark et al, 2005; Kilgallon et al, 2007; Potier et al, 2009; Reeves et al, 2009; Brughelli et al, 2010; Martínez-Ruiz et al, 2014; Guex et al, 2016; Timmins et al, 2016a). Recent detailed evidence suggest a possible role of region-specific muscle hypertrophy in addition to a neural mechanism (Noorkoiv et al, 2014)

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