Seasonal timing on a cyclical Earth: Towards a theoretical framework for the evolution of phenology.

Phenology refers to the seasonal timing patterns commonly exhibited by life on Earth, from blooming flowers to breeding birds to human agriculture. Climate change is altering abiotic seasonality (e.g., longer summers) and in turn, phenological patterns contained within. However, how phenology should evolve is still an unsolved problem. This problem lies at the crux of predicting future phenological changes that will likely have substantial ecosystem consequences, and more fundamentally, of understanding an undeniably global phenomenon. Most studies have associated proximate environmental variables with phenological responses in case-specific ways, making it difficult to contextualize observations within a general evolutionary framework. We outline the complex but universal ways in which seasonal timing maps onto evolutionary fitness. We borrow lessons from life history theory and evolutionary demography that have benefited from a first principles-based theoretical scaffold. Lastly, we identify key questions for theorists and empiricists to help advance our general understanding of phenology.

Herbivory and warming interact in opposing patterns of covariation between arctic shrub species at large and local scales.

A major challenge in predicting species' distributional responses to climate change involves resolving interactions between abiotic and biotic factors in structuring ecological communities. This challenge reflects the classical conceptualization of species' regional distributions as simultaneously constrained by climatic conditions, while by necessity emerging from local biotic interactions. A ubiquitous pattern in nature illustrates this dichotomy: potentially competing species covary positively at large scales but negatively at local scales. Recent theory poses a resolution to this conundrum by predicting roles of both abiotic and biotic factors in covariation of species at both scales, but empirical tests have lagged such developments. We conducted a 15-y warming and herbivore-exclusion experiment to investigate drivers of opposing patterns of covariation between two codominant arctic shrub species at large and local scales. Climatic conditions and biotic exploitation mediated both positive covariation between these species at the landscape scale and negative covariation between them locally. Furthermore, covariation between the two species conferred resilience in ecosystem carbon uptake. This study thus lends empirical support to developing theoretical solutions to a long-standing ecological puzzle, while highlighting its relevance to understanding community compositional responses to climate change.

Divergence of Arctic shrub growth associated with sea ice decline.

Arctic sea ice extent (SIE) is declining at an accelerating rate with a wide range of ecological consequences. However, determining sea ice effects on tundra vegetation remains a challenge. In this study, we examined the universality or lack thereof in tundra shrub growth responses to changes in SIE and summer climate across the Pan-Arctic, taking advantage of 23 tundra shrub-ring chronologies from 19 widely distributed sites (56°N to 83°N). We show a clear divergence in shrub growth responses to SIE that began in the mid-1990s, with 39% of the chronologies showing declines and 57% showing increases in radial growth (decreasers and increasers, respectively). Structural equation models revealed that declining SIE was associated with rising air temperature and precipitation for increasers and with increasingly dry conditions for decreasers. Decreasers tended to be from areas of the Arctic with lower summer precipitation and their growth decline was related to decreases in the standardized precipitation evapotranspiration index. Our findings suggest that moisture limitation, associated with declining SIE, might inhibit the positive effects of warming on shrub growth over a considerable part of the terrestrial Arctic, thereby complicating predictions of vegetation change and future tundra productivity.

Team USA injury and illness incidence at the 2022 Beijing Winter Olympic and Paralympic Games.

OBJECTIVE: The purpose of this study was to determine the injury and illness incidence from Team USA athletes from the 2022 Beijing Winter Olympic and Paralympic Games and assess any sex-based differences or differences between Olympic and Paralympic athletes. METHODS: Team USA Olympic (n=231, 48.5% female) and Team USA Paralympic (n=63, 22.2% female) athletes had medical encounters documented during the Games. Injuries and illnesses were defined according to the 2020 International Olympic Committee Consensus Statement and reviewed for accuracy by a physician. Incidence rates were calculated per 1000 athlete-days and further analysed by sex, sport, anatomical location, type of illness, injury event and injury mechanism, with incident rate ratios (IRRs) used for group comparisons. RESULTS: There were no differences in illness (Olympic illness, IRR=0.99 (95% CI 0.48 to 2.07), p=0.998; Paralympic illness, IRR=1.43 (95% CI 0.41 to 4.97), p=0.572) or injury rates (Olympic injury, IRR=0.63 (95% CI 0.39 to 1.03), p=0.062; Paralympic injury, IRR=1.01 (95% CI 0.43 to 2.35), p=0.988) between male and female (reference group) athletes. However, Olympic athletes had significantly lower illness (IRR=0.41 (95% CI 0.22 to 0.76), p=0.003) and injury (IRR=0.56 (95% CI 0.37 to 0.87), p=0.009) risks compared with Paralympic athletes. CONCLUSION: No significant sex-related differences in injury or illness were detected in Team USA Olympic or Paralympic participating in the 2022 Beijing Winter Games. However, Paralympic athletes exhibited higher rates of injury and illness compared with their Olympic counterparts. This study highlights delegation-specific epidemiological data which may facilitate more focused approaches for injury and illness prevention.

Parent decision-making regarding youth sport participation during the COVID-19 pandemic.

PURPOSE: To describe youth sport participation behaviors during the COVID-19 pandemic as reported by parents of youth sport athletes, to examine the association of family demographics with the likelihood of children resuming sports, and to qualitatively report the factors influencing parental decision-making regarding youth sport participation during the COVID-19 pandemic. METHODS: A national sample of parents of youth athletes from across the United States (n=236, age: 39.2±8.1 years, 57.2% female) were recruited to complete an online questionnaire by Qualtrics Online Samples (Qualtrics, Provo, UT) using a combination of actively managed, double-opt-in market research panels. The questionnaire focused on changes in child sport participation and family finances as a result of COVID-19 and included both close-ended and open-ended questions. RESULTS: Most parents (63.1%) reported the time their children spent participating in organized youth sports had decreased because of the COVID-19 pandemic. Three-quarters of parents (75.5%) reported that it was likely that their children would fully resume participating in organized youth sports within the next year. Parents whose financial situation was worsened by COVID-19 were less likely to report that their children would resume sports in the upcoming year. Three domains related to parental decision-making emerged from the open-ended responses: safety, fear, and normalcy. CONCLUSIONS: Understanding the factors influencing changes in youth sport participation during the pandemic can allow systems to implement strategies for safe participation in youth sport and physical activity among children. Encouraging participation in outdoor sports with appropriate safety precautions such as masking, social distancing, and hygiene may reduce fear of participation among parents.

Differences in Sport-Related Concussion History, Reporting Behavior, and Return to Learn and Sport Timelines in Public versus Private High School Student Athletes.

Objective: To compare: 1) history of sport-related concussion (SRC), 2) Return to learn (RTL) timelines, 3) Return to play (RTP) timelines, and 4) SRC reporting behaviors in high-school student athletes based on school type (public vs. private).Methods: A total of 2,998 athletes recruited from eleven private (n = 2121) and two public schools (n = 877) during the 2018-2019 school year completed an online questionnaire regarding sport participation and SRC history. The questionnaire examined self-reported history of SRC, reporting behavior, and RTL and RTP timelines.Results: Private school athletes were approximately twice as likely to report a history of SRC compared to public school athletes (OR [95% CI]: 2.01 [1.61-2.50], p < .001). There were no significant differences in RTL or RTP timelines between public and private-school athletes (p > .05). For those who did not report their SRC (22.4%), the most common reasons were "a desire to keep playing" (53.7%) and "not believing it was serious enough to report" (52.1%).Conclusions: Athletic trainers and healthcare professionals should be aware of the factors that may influence secondary student athletes' SRC reporting behavior, and associated RTL, and RTP timelines, so they can better target concussion education and overall management for student-athletes.Abbreviations: SRC: Sport-related concussion; RTP: Return to play; RTL: Return to learn.

Impact of in-season injury on quality of life and sleep duration in female youth volleyball athletes: a prospective study of 2073 players.

OBJECTIVES: The psychological impacts of injuries in youth athletes remain poorly defined. The purpose of this study was to evaluate the influence of injury on quality of life (QOL) and sleep in female high school volleyball athletes. METHODS: 2073 female high school volleyball players (15.6±1.1 years) completed the Pediatric Quality of Life survey (total QOL, physical, social, school, emotional and psychosocial function) and reported average sleep duration at the start and end of the season. Injury data were collected by school athletic trainers. Mixed effects linear regression models were used to compare changes in QOL and sleep duration during the season between (1) injured and uninjured athletes and (2) injured athletes who did or did not suffer a season-ending injury. RESULTS: Time-loss injuries were reported in 187 athletes with complete preseason and postseason data. During the season, injured athletes demonstrated a greater decrease in total QOL (ß=-1.3±0.5, p=0.012), as well as physical function (ß=-1.6±0.6, p=0.012), school function (ß=-2.0±0.76, p=0.01) and psychosocial function domains (ß=-1.2±0.6, p=0.039) compared with uninjured athletes. Athletes who sustained a season-ending injury had a significantly greater decrease in total QOL (ß=-6.8±2.0, p=0.006) and physical function (ß=-17±2.9, p<0.001) compared with injured athletes who were able to return to play during the season. CONCLUSION: In-season injuries are associated with significant decreases in total QOL as well as physical and psychosocial function. Healthcare providers should consider the impacts of injuries on QOL and sleep in youth athletes in order to optimise management and improve overall health.

Sport Specialization Behaviors Are Associated With History of Reported Injury in Youth Basketball.

BACKGROUND: There is significant emerging evidence that early sport specialization is a potential risk factor for injury in youth sports. Despite basketball being the most popular youth team sport in the United States, sport specialization research, specifically in youth basketball players, has been limited. The purpose of this paper was to examine the association of sport specialization behaviors with injury history by surveying a nationally representative sample of parents of youth basketball athletes. We hypothesized that athletes who specialized in basketball, participated on multiple teams at the same time, and traveled regularly for basketball competitions would be more likely to report a basketball-related injury in the previous year. METHODS: A nationally representative sample of 805 parents of 805 youth basketball players (female N=241, 29.9%; age: 12.9±2.5 y old) completed an online questionnaire that had 3 sections: (1) parent/child demographics, (2) child basketball participation information for the previous year, and (3) child basketball injury history in the previous year. Multivariate logistic regression examined the associations between variables of interest and injury history, adjusting for covariates. Odds ratios (ORs) with 95% confidence intervals (95% CI) were calculated for the variables of interest from the logistic regression model. RESULTS: Highly specialized athletes were more likely than low specialization athletes to report history of basketball injury in the previous year [OR (95% CI): 2.47 (1.25-4.88), P=0.009]. The odds of reporting an injury in the previous year were twice as great among athletes who played on a basketball team at the same time as another sport team compared with those who played basketball only [OR (95% CI): 1.98 (1.30-3.01), P=0.001]. The odds of reporting an injury in the previous year were 3 times greater among athletes who received private coaching compared with those who did not receive private coaching [OR (95% CI): 2.91 (1.97-4.31), P<0.001]. CONCLUSION: Specialization in basketball, along with several other behaviors that have become typical of modern youth sport participation, were associated with reported injury history. Further prospective research is necessary to determine whether sport specialization behaviors increase the risk of injury in youth basketball. LEVEL OF EVIDENCE: Level III-cross-sectional study.

Does soccer headgear reduce the incidence of sport-related concussion? A cluster, randomised controlled trial of adolescent athletes.

BACKGROUND: There have been no large randomised controlled trials to determine whether soccer headgear reduces the incidence or severity of sport-related concussion (SRC) in US high school athletes. OBJECTIVE: We aimed to determine whether headgear reduces the incidence or severity (days out from soccer) of SRCs in soccer players. METHODS: 2766 participants (67% female, age 15.6±1.2) (who undertook 3050 participant years) participated in this cluster randomised trial. Athletes in the headgear (HG) group wore headgear during the season, while those in the no headgear (NoHG) group did not. Staff recorded SRC and non-SRC injuries and soccer exposures. Multivariate Cox proportional hazards models were used to examine time-to-SRC between groups, while severity was compared with a Wilcoxon rank-sum test. RESULTS: 130 participants (5.3% female, 2.2% male) sustained an SRC. The incidence of SRC was not different between the HG and NoHG groups for males (HR: 2.00 (0.63-6.43) p=0.242) and females (HR: 0.86 (0.54-1.36) p=0.520). Days lost from SRC were not different (p=0.583) between the HG group (13.5 (11.0-018.8) days) and the NoHG group (13.0 (9.0-18.8) days). CONCLUSIONS: Soccer headgear did not reduce the incidence or severity of SRC in high school soccer players. TRIAL REGISTRATION NUMBER: NCT02850926.

Parents' Awareness and Perceptions of Sport Specialization and Injury Prevention Recommendations.

OBJECTIVE: To conduct a survey of parents to determine their knowledge of sport volume recommendations and examine their perceptions toward sport specialization. DESIGN: Cross-sectional survey. SETTING: Youth sport athletic tournaments, competitions, and practices. PATIENTS OR OTHER PARTICIPANTS: Parents (n = 1000, 614 women, age: 44.5 ± 6.7 years) of youth athletes completed the survey. Parents had to have a child between 10 and 18 years of age who participated in organized sport in the previous 12 months. INTERVENTIONS: The survey was anonymous and consisted of yes/no and Likert-scale questions and consisted of background of parent and child and perceptions and knowledge of safe sport recommendations. An expert panel validated the survey. MAIN OUTCOME MEASURES: Data were summarized by frequencies, proportions (%), and mean values and SDs, when appropriate. Chi-square analyses were used to determine if parent sex influenced distributions. RESULTS: Over 80% of parents had no knowledge of sport volume recommendations regarding h/wk (84.5%), mo/yr (82.2%), or simultaneous participation in multiple leagues (89.9%). Twenty-four percent of parents considered it appropriate to participate in multiple leagues in the same sport, whereas 60.5% considered it appropriate to participate in multiple leagues of a different sport. Thirty-four percent of parents indicated that they were concerned about the risk of injury in youth sports. Although 55% of parents considered sport specialization a problem in youth sports, only 43.3% thought that year-round sport participation increased the chances of sustaining an overuse injury. Female parents were more likely to be concerned about injury and believe that year-round sport participation results in overuse injury compared with men. CONCLUSIONS: Recommendations associated with youth sport participation are not well known. However, parents are concerned about the risk of injury and consider sport specialization a problem.

Sport specialization is associated with upper-extremity overuse injury in high school baseball players.

BACKGROUND AND HYPOTHESIS: Sport specialization is increasingly common in youth sports and is a risk factor for lower-extremity overuse injuries. However, limited data exist on whether specialization is associated with upper-extremity (UE) overuse injuries, specifically in youth baseball players. We hypothesized that specialization in baseball and being a pitcher would be associated with poorer arm health and UE overuse injury history in the previous year. METHODS: During the 2019 spring baseball season, 551 high school baseball athletes (aged 15.9 ± 1.3 years) from 3 states (Alabama, n = 200; California, n = 188; and Michigan, n = 163) completed an anonymous questionnaire. Athletes were recruited from 5 high schools in each state, with schools matched based on factors that influence specialization rates. The questionnaire consisted of (1) demographic characteristics, (2) baseball participation information (including sport specialization status), and (3) throwing-arm health and UE injury history in the previous 12 months. Throwing-arm health was assessed using the Youth Throwing Score (YTS), a validated and reliable outcome measure for youth baseball players. Multivariate regression analyses were used to examine the association between variables of interest and the YTS or UE overuse injury history, adjusting for covariates. RESULTS: After adjustment for covariates, highly specialized athletes were more likely to report a UE overuse injury in the previous year compared with low-specialization athletes (odds ratio [OR], 3.77; 95% confidence interval [CI], 1.39-10.2, P = .009). Both athletes who reported playing baseball for more than 8 months per year (OR, 2.03; 95% CI, 1.12-3.65; P = .019) and athletes who reported being a pitcher (OR, 2.11; 95% CI, 1.20-3.72; P = .010) were more likely to report a history of UE overuse injury. Highly specialized players reported lower (worse) YTS values compared with low-specialization players (least-squares mean estimate ± standard error, 56.5 ± 1.1 vs. 53.3 ± 0.7; P = .034). Players who reported pitching as one of their positions scored worse on the YTS than non-pitchers (least-squares mean estimate ± standard error, 51.6 ± 0.8 vs. 57.2 ± 0.6; P < .001). CONCLUSION: Although baseball recommendations that discourage sport specialization are widely available for parents, athletes, and coaches, high rates of sport specialization were reported in our sample. We found that being highly specialized in baseball was associated with UE overuse injury history and worse throwing-arm health in high school baseball athletes. Continued education for baseball parents, athletes, and coaches is necessary to raise awareness of the risks associated with high specialization.

Knowledge, Attitudes, and Beliefs of Youth Sports Coaches Regarding Sport Volume Recommendations and Sport Specialization.

Post, EG, Trigsted, SM, Schaefer, DA, Cadmus-Bertram, LA, Watson, AM, McGuine, TA, Brooks, MA, and Bell, DR. Knowledge, attitudes, and beliefs of youth sports coaches regarding sport volume recommendations and sport specialization. J Strength Cond Res 34(10): 2911-2919, 2020-Overuse injuries in youth athletes are becoming increasingly common, which may be a result of the prevalence of year-round specialized sport participation. Previous research has identified sport volume recommendations related to months per year, hours per week, and simultaneous participation in multiple sports leagues. Coaches are a primary influence on a youth athlete's decision to specialize in a single sport. Therefore, identifying coaches' baseline beliefs and perceptions is important for developing strategies to educate coaches about safe sport participation. A total of 253 youth sport coaches (207 males) completed an anonymous online questionnaire regarding knowledge of sport volume recommendations and attitudes and beliefs regarding sport specialization. Eligible participants were required to serve as a head or assistant coach of a youth sport team in the past 12 months whose members were between the ages of 12 and 18 years. Most coaches were unaware of recommendations regarding the maximum number of months per year (79.4%), hours per week in 1 sport (79.3%), or number of simultaneous leagues for an athlete to participate in to reduce injury (77.6%). Fewer than half (43.2%) of all coaches were "very" or "extremely" concerned about the risk of injury in youth sports. A majority (60.1%) believed that sport specialization was either "quite a bit" or "a great deal" of a problem. Two-thirds (67.2%) responded that year-round participation in a single sport was either "very" or "extremely" likely to increase an athlete's risk of injury. Although the responses to this survey were predominantly from coaches from 1 state, our results suggest that coaches are unaware of sport volume recommendations but are concerned about specialization. Future efforts are needed to communicate these recommendations to coaches to reduce the risk of overuse injury in youth sports.

Different Perceptions of Parents and Children on Factors Influencing Sport Specialization.

CONTEXT: Sport specialization among youth athletes has been associated with increased risk of overuse injuries. Previous research demonstrates that children perceive specialization to be beneficial in making their high school team and receiving athletic college scholarships. Previous research demonstrates that parents play a significant role in their child's sport experience. However, it is unknown if parents and children answer questions related to specialization factors in a similar manner. OBJECTIVE: To evaluate the beliefs of youth athletes and parents on factors related to sport specialization and evaluate the level of agreement between dyads on sports specialization. DESIGN: Cross-sectional. SETTING: Online and paper surveys. PATIENTS OR OTHER PARTICIPANTS: Aim 1: 1998 participants (993 children and 1005 parents). Aim 2: 77 paired parent-child dyads. INTERVENTIONS: Self-administered survey. MAIN OUTCOME MEASURES: The responses were summarized via frequency and proportions (%). Chi-squares were calculated between parent and child responses. Kappa coefficients were calculated for dyads to determine level of agreement. Sport specialization was classified using a common 3-point scale. RESULTS: The parents were more concerned about risk of injury in sports compared with children (P < .001, χ2 = 231.4; parent: extremely: 7.1%; child: extremely: 3.7%). However, children were more likely to believe that specialization was associated with their chances of obtaining an athletic college scholarship compared with parents (P < .001, χ2 = 201.6; parent: very/extremely likely: 13.7%; child: very/extremely likely: 15.8%). Dyad subanalysis indicated a moderate level of agreement for "quitting other sports to focus on one sport" (κ = .50) and a low level of agreement for "identifying a primary sport" (κ = .30) and "training >8 months per year in primary sport" (κ = .32). CONCLUSIONS: Parents and youth athletes had differing beliefs on the factors related to sport specialization. Dyad analysis shows that parents and children answer sport specialization classification questions differently. Health care providers should be aware of these differences, and messaging should be individualized to the audience.

Corrigendum: Internet Blogs, Polar Bears, and Climate-Change Denial by Proxy.

[This corrects the article DOI: 10.1093/biosci/bix133.].

Internet Blogs, Polar Bears, and Climate-Change Denial by Proxy.

Increasing surface temperatures, Arctic sea-ice loss, and other evidence of anthropogenic global warming (AGW) are acknowledged by every major scientific organization in the world. However, there is a wide gap between this broad scientific consensus and public opinion. Internet blogs have strongly contributed to this consensus gap by fomenting misunderstandings of AGW causes and consequences. Polar bears (Ursus maritimus) have become a "poster species" for AGW, making them a target of those denying AGW evidence. Here, focusing on Arctic sea ice and polar bears, we show that blogs that deny or downplay AGW disregard the overwhelming scientific evidence of Arctic sea-ice loss and polar bear vulnerability. By denying the impacts of AGW on polar bears, bloggers aim to cast doubt on other established ecological consequences of AGW, aggravating the consensus gap. To counter misinformation and reduce this gap, scientists should directly engage the public in the media and blogosphere.

Effects of sea ice on Arctic biota: an emerging crisis discipline.

The rapid decline in Arctic sea ice (ASI) extent, area and volume during recent decades is occurring before we can understand many of the mechanisms through which ASI interacts with biological processes both at sea and on land. As a consequence, our ability to predict and manage the effects of this enormous environmental change is limited, making this a crisis discipline Here, we propose a framework to study these effects, defining direct effects as those acting on life-history events of Arctic biota, and indirect effects, where ASI acts upon biological systems through chains of events, normally involving other components of the physical system and/or biotic interactions. Given the breadth and complexity of ASI's effects on Arctic biota, Arctic research requires a truly multidisciplinary approach to address this issue. In the absence of effective global efforts to tackle anthropogenic global warming, ASI will likely continue to decrease, compromising the conservation of many ASI-related taxonomic groups and ecosystems. Mitigation actions will rely heavily on the knowledge acquired on the mechanisms and components involved with the biological effects of ASI.

Greater temperature sensitivity of plant phenology at colder sites: implications for convergence across northern latitudes.

Warmer temperatures are accelerating the phenology of organisms around the world. Temperature sensitivity of phenology might be greater in colder, higher latitude sites than in warmer regions, in part because small changes in temperature constitute greater relative changes in thermal balance at colder sites. To test this hypothesis, we examined up to 20 years of phenology data for 47 tundra plant species at 18 high-latitude sites along a climatic gradient. Across all species, the timing of leaf emergence and flowering was more sensitive to a given increase in summer temperature at colder than warmer high-latitude locations. A similar pattern was seen over time for the flowering phenology of a widespread species, Cassiope tetragona. These are among the first results highlighting differential phenological responses of plants across a climatic gradient and suggest the possibility of convergence in flowering times and therefore an increase in gene flow across latitudes as the climate warms.

The Arctic in the Twenty-First Century: Changing Biogeochemical Linkages across a Paraglacial Landscape of Greenland.

The Kangerlussuaq area of southwest Greenland encompasses diverse ecological, geomorphic, and climate gradients that function over a range of spatial and temporal scales. Ecosystems range from the microbial communities on the ice sheet and moisture-stressed terrestrial vegetation (and their associated herbivores) to freshwater and oligosaline lakes. These ecosystems are linked by a dynamic glacio-fluvial-aeolian geomorphic system that transports water, geological material, organic carbon and nutrients from the glacier surface to adjacent terrestrial and aquatic systems. This paraglacial system is now subject to substantial change because of rapid regional warming since 2000. Here, we describe changes in the eco- and geomorphic systems at a range of timescales and explore rapid future change in the links that integrate these systems. We highlight the importance of cross-system subsidies at the landscape scale and, importantly, how these might change in the near future as the Arctic is expected to continue to warm.

Landing mechanics during single hop for distance in females following anterior cruciate ligament reconstruction compared to healthy controls.

PURPOSE: To determine possible differences in single-hop kinematics and kinetics in females with anterior cruciate ligament reconstruction compared to healthy controls. A second purpose was to make comparisons between the healthy and reconstructed limbs. METHODS: Subjects were grouped based on surgical status (33 ACLR patients and 31 healthy controls). 3D motion capture synchronized with force plates was used to capture the landing phase of three successful trials of single hop for distance during a single data collection session. Peak values during the loading phase were analysed. Subjects additionally completed three successful trials of the triple hop for distance Tegner activity scale and International Knee Document Committee 2000 (IKDC). RESULTS: Controls demonstrated greater peak knee flexion and greater internal knee extension moment and hip extension moment than ACLR subjects. Within the ACLR group, the healthy limb exhibited greater peak knee flexion, hip flexion, hip extension moment, single hop and triple hops for distance and normalized quadriceps strength. CONCLUSION: Patients who undergo anterior cruciate ligament reconstruction land in a more extended posture when compared to healthy controls and compared to their healthy limb. LEVEL OF EVIDENCE: III.

The Reliability and Discriminative Ability of the Overhead Squat Test for Observational Screening of Medial Knee Displacement.

CONTEXT: The overhead squat test (OHS) is a functional screening exam that is used to identify high-risk movement profiles such as medial knee displacement (MKD). The reliability and discriminative ability of observational screening during the OHS to identify MKD have yet to be established. OBJECTIVE: To investigate the reliability and discriminative ability of observational screening for medial knee displacement MKD during the OHS. STUDY DESIGN: Clinical measurement, cross sectional. PARTICIPANTS: 100 college students were video-recorded performing the OHS. Three certified athletic trainers classified the knee posture of each subject during the OHS on 2 different occasions using screening guidelines. MAIN OUTCOME MEASURES: Ratings were evaluated by calculating kappa coefficients for intra- and interrater levels of agreements. MKD was measured using motion analysis. RESULTS: Intrarater reliability ranged from .60-.76 with an average value of .70. Interrater reliability was substantial (kappa > .60) for both observation sessions (Fleiss kappa session 1 = .69, session 2 = .70). Sensitivity ranged was .58-.83, while specificity ranged was .70-.88. The MKD group displayed significantly more displacement than the no-MKD group (p < .001). There was a moderate positive correlation (r = .48, p < .001) between knee-posture group and MKD assessed using motion analysis. CONCLUSION: The OHS has substantial reliability and is able to assess the presence of MKD. The OHS should be used as part of a comprehensive examination that evaluates multiple movement patterns and risk levels.