AUTHOR=Jordan Matthew J. , Morris Nathaniel , Nimphius Sophia , Aagaard Per , Herzog Walter 

TITLE=Attenuated Lower Limb Stretch-Shorten-Cycle Capacity in ACL Injured vs. Non-Injured Female Alpine Ski Racers: Not Just a Matter of Between-Limb Asymmetry

JOURNAL=Frontiers in Sports and Active Living

VOLUME=Volume 4 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2022.853701

DOI=10.3389/fspor.2022.853701

ISSN=2624-9367

ABSTRACT=A retrospective analysis of routine countermovement jump (CMJ) testing, a coupled eccentric-concentric (slow-stretch-shortening-cycle: SSC) movement, was performed in female elite alpine skiers with (ACLR) and without anterior cruciate ligament (ACL) reconstruction. A total of 567 tests obtained from the daily training environment were analyzed in 41 elite female athletes (non-injured control: n= 30; ACLR: n=17; participants with pre-injury data= n=6) between 16 to 32 years of age from alpine ski racing (n=32), and skier cross (n=9). Bilateral CMJ testing was conducted on a dual force plate system, and limb-specific vertical ground reaction force (Fz) was analyzed to obtain the net eccentric deceleration impulse (Ecc), lower limb stiffness (Stiff), maximal vertical jump height (JH), system peak external mechanical power (PP), modified-reactive-strength-index (RSImod), and the loss in body centre of mass (BCM) velocity during the final phase of the takeoff ([Vmax-Vtakeoff]). Eccentric and concentric phase-specific between-limb asymmetry indexes (AI) were also calculated. Generalized additive mixed models (GAMM) were applied to compare the age-dependent and post-injury time course change between groups. The mean values for non-injured controls > 25 years of age were used as a comparative benchmark for recovery given the absence of pre-injury data. Net eccentric deceleration impulse increased and [Vmax-Vtakeoff] decreased with increasing age for the non-injured controls (P<0.001) while between-limb AI (mean  SD) fell between 15% for the concentric phase and 37% for the eccentric deceleration phase. Between-limb asymmetry became smaller in ACLR with time-from-surgery to reach non-injured control values by two years, but SSC function including JH and PP remained depressed up to 5 years post-surgery (P<0.01), suggesting impairments in slow-SSC function. This highlights the importance of considering slow-SSC performance capacity alongside vertical jump force-time asymmetries in female ACLR alpine skiers.