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PURPOSE: Prediction of athlete wellness is difficult-or, many sports-medicine practitioners and scientists would argue, impossible. Instead, one settles for correlational relationships of variables gathered at fixed moments in time. The issue may be an inherent mismatch between usual methods of data collection and analysis and the complex nature of the variables governing athlete wellness. Variables such as external load, stress, muscle soreness, and sleep quality may affect each other and wellness in a dynamic, nonlinear, way over time. In such an environment, traditional data-collection methods and statistics will fail to capture causal effects. If we are to move this area of sport science forward, a different approach is required. METHODS: We analyzed data from 2 different soccer teams that showed no significance between player load and wellness or among individual measures of wellness. Our analysis used methods of attractor reconstruction to examine possible causal relationships between GPS/accelerometer-measured external training load and wellness variables. RESULTS: Our analysis showed that player self-rated stress, a component of wellness, seems a fundamental driving variable. The influence of stress is so great that stress can predict other components of athlete wellness, and, in turn, self-rated stress can be predicted by observing a player's load data. CONCLUSION: We demonstrate the ability of nonlinear methods to identify interactions between and among variables to predict future athlete stress. These relationships are indicative of the causal relationships playing out in athlete wellness over the course of a soccer season.

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Stress fractures likely have a 1-2% incidence in athletes in general. In runners, a more vulnerable population, incidence rates likely range between 3.2 and 21% with female runners having greater susceptibility. The incidence of femoral shaft stress fractures is less well known. New basic and translational science research may impact the way clinicians diagnose and treat femoral stress fractures. By using a fictitious case study, this paper applies bone science to suggest new approaches to evaluating and treating femoral shaft stress fractures in the running population.

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Rehabilitation professionals prescribe exercise regularly with the goals of decreasing pain, increasing function, and returning athletes to competition. To maximize the effect of an exercise intervention, the program must be individualized and in context for the athlete considering biopsychosocial aspects of care. Current models of exercise prescription may not be ideal considering that less than 50% of injured athletes return to their pre-injury level. Advice on exercise prescription has been offered in the past, but the paradigms are either not user friendly or user friendly but linear, based on phases of recovery. As such, there is a need for a more flexible exercise prescription paradigm that should improve the individuality of exercise prescription. In this Current Opinion, we offer a user-friendly construct-oriented paradigm designed to facilitate the creation of individualized exercise programs for athletes.

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The sports medicine literature is filled with associations between injury and causal factors. However, those results have been inconsistent. We're left wondering which of our athletes might need more attention and where our efforts might be best spent. Resistance to injury is the result of interaction between many variables. These variables are interdependent with dynamic relationships which can be sometimes correlated, at times anti-correlated and from time to time show no relationship with injury risk. Relationships we may have seen yesterday do not necessarily hold true for today and we should not use those to infer what will happen. This perspective piece builds on prior works and describes how the complex interaction between injury determinants presents in other systems, why determinants are not stable and instead vary over time due to internal and external forcing and why our prediction ability remains limited even when determinants are identified. Patterns built from frequent time series data in conjunction with nonlinear dynamical methods can offer us a new approach to thinking about injury prediction.

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STUDY DESIGN: Systematic review. OBJECTIVE: To quantify variability in undesirable outcomes among studies of lumbar interbody fusion using stand-alone cage devices, and to determine whether author conflicts of interest contribute to variability. SUMMARY OF BACKGROUND DATA: Promising early studies of lumbar fusion with stand-alone cage devices led to rapid uptake of the technique, but some surgeons later expressed reservations regarding efficacy and safety. METHODS: We systematically identified studies of lumbar interbody fusion with stand-alone cage devices that reported at least one undesirable outcome among 10 or more adult subjects. We performed meta-analyses of rates of 7 prespecified outcomes (nonunion, reoperation, major vessel injury, retrograde ejaculation, neurologic injury, dural injury, and infection). Heterogeneity in outcome rates was quantified as I2 (the proportion of variance due to differences among studies rather than random variation). Random-effects meta-regression identified sources of observed heterogeneity, including potential conflicts of interest. RESULTS: We identified 30 eligible studies, including a total of 3228 subjects. A potential conflict of interest was identified in 18 (60%). We observed marked heterogeneity in rates of nonunion, reoperation, and neurologic injury (I2 > 85%; P < 0.001), and substantial heterogeneity in rates of dural injury (I2 = 63%; P < 0.01) and major vessel injury (I2 = 38%; P = 0.09). Among 24 studies reporting fusion status after 6 months of follow-up, nonunion rates ranged from 2.3% to 83.3% (median, 8.3%) and exceeded 45% in 4 studies. Potential author conflict of interest was associated with significantly lower rates of nonunion (P = 0.001). Heterogeneity in rates of other undesirable outcomes was not significantly associated with author conflicts of interest or other study characteristics. CONCLUSION: We quantified substantial unexplained variation in reported complication rates of undesirable outcomes of lumbar interbody fusion with stand-alone cage devices. Authors with potential conflicts of interest, however, reported significantly lower rates of nonunion.

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