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Overall, more men sustained ACL injury in football. There was no difference in the relative risk of ACL injury between female and male football players in a window that spanned one season to 4 years. The IR of ACL injury among women was 2.2 times higher than the IR of ACL injury among men. The reported sex disparity in ACL injury was independent of participation level.

Researchers have demonstrated that a person's rhythmic movements can become unintentionally entrained to another person's rhythmic movements or an environmental event. There are indications, however, that in both cases the likelihood of entrainment depends on the difference between the uncoupled periods of the two rhythms. The authors examined the range of period differences over which unintentional visual coordination might occur in 16 participants (Experiment 1) and 15 participants (Experiment 2). Cross-spectral coherence analysis and the distribution of continuous relative phase revealed that visual entrainment decreased as the difference between participants' preferred period and the experimenter-determined period of the environmental stimulus increased. The present findings extend the dynamical systems perspective on person-environment coupling and highlight the significance of period difference to the emergence of unintentional coordination.

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This commentary focuses on a complementary theoretical-experimental approach to the target article by Hill, Den Hartigh, Meijer, De Jonge, and Van Yperen (2018). In the target article, the authors develop an initial roadmap for identifying persistent behavioral patterns (i.e., athletic resilience) through measurements to identify specific attractor states and/or the attractor landscape. The goal of this approach is to promote a more complete understanding of the underlying attractor dynamics that give rise to resilient behavior. We extend the thesis of the target article via the concept of metastability. Metastable dynamics are the result of the system remaining poised on the edge of criticality. We argue that metastability is key for positively adapted behavior and, ultimately, successful athletic performance. When considered in this light, positive adaptations to adversity (i.e., resilience) are the minimum outcome, with performance enhancement in the face of adversity as the true performance goal. Such growth from adversity is termed antifragility. We next couch this concept in the context of evolutionary biology to leverage biological hormesis as a stress-response model for athletic performance. This allows for biology-inspired fitness profiles that provide a quantifiable measure of stress response relative to environmental change. From there, phenotypic plasticity can be calculated to further elucidate the relation between adversity and performance responses as a quantifiable index of antifragility. Finally, this approach is discussed in the context of personalized training interventions that facilitate the emergence of metastable dynamics that underlie phenotypic plasticity, with critical training windows introduced as opportunities to increase athletic antifragility.

Context: A limiting factor for reducing anterior cruciate ligament injury risk is ensuring that the movement adaptions made during the prevention program transfer to sport-specific activity. Virtual reality provides a mechanism to assess transferability, and neuroimaging provides a means to assay the neural processes allowing for such skill transfer. Objective: To determine the neural mechanisms for injury risk–reducing biomechanics transfer to sport after anterior cruciate ligament injury prevention training. Design: Cohort study. Setting: Research laboratory. Participants: Four healthy high school soccer athletes. Interventions: Participants completed augmented neuromuscular training utilizing real-time visual feedback. An unloaded knee extension task and a loaded leg press task were completed with neuroimaging before and after training. A virtual reality soccer-specific landing task was also competed following training to assess transfer of movement mechanics. Main Outcome Measures: Landing mechanics during the virtual reality soccer task and blood oxygen level–dependent signal change during neuroimaging. Results: Increased motor planning, sensory and visual region activity during unloaded knee extension and decreased motor cortex activity during loaded leg press were highly correlated with improvements in landing mechanics (decreased hip adduction and knee rotation). Conclusion: Changes in brain activity may underlie adaptation and transfer of injury risk–reducing movement mechanics to sport activity. Clinicians may be able to target these specific brain processes with adjunctive therapy to facilitate intervention improvements transferring to sport.

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