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State Dependence: Does a Prior Injury Predict a Future Injury?
Abstract
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 explain how the complex interaction of 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.
... This model offers principles for understanding and modelling complex, dynamic and non-linear scenarios, such as those that occur in sports (Pol et al., 2019). The interaction between the aforementioned risk factors during different time frames makes sport injuries a non-linear problem (Stern et al., 2021). The traditional statistical approach has been based on the existence of a linear causality (Stern et al., 2021), with many of the studies emphasising external loads as the main risk factor. ...
... The interaction between the aforementioned risk factors during different time frames makes sport injuries a non-linear problem (Stern et al., 2021). The traditional statistical approach has been based on the existence of a linear causality (Stern et al., 2021), with many of the studies emphasising external loads as the main risk factor. However, these models have had little success in their practical implementation since sport injuries are a complex phenomenon (Bittencourt et al., 2016). ...
... The evidence supports the idea that a previous injury is one of the strongest factors to provoke a future injury (Stern et al., 2021;Wylde et al., 2022). An injury history can lead to somatosensory, neuromuscular and biomechanical adaptations with associated deficits over a long period of time (Needle et al., 2016;Rio et al., 2020;Tayfur et al., 2021). ...
This study investigates whether the presence of a previous lower limb injury influences “Lower limb asymmetry” (LLA) in elite basketball players. A prospective, longitudinal observational study was carried out with 13 players grouped based on lower limb injury history in the 3 months prior to the study (Injury = 7, non-injured = 6). A total of 68 measurements per player were collected over 3 months, using the “Inertial Measurement Unit (IMU)” device. The mean difference in, (i) % of step balance; (ii) the average of the number of impacts performed per minute during training and (iii) the player’s load was assessed. This intensive evaluation is in line with the assessment methodology proposed in the field of sports injury. Our results show no significant differences (p = 0.377) in the asymmetry of the step balance between players with/without a history of injury. However, there were differences when the player’s position was considered (p = 0.046). These findings confirm that the presence of a previous lower limb injury does not influence the asymmetry in lower limb step balance in male basketball players. For clinicians, the variables studied offer an indirect measurement of any capacity and/or deficit in the absorption of lower limb loads after an injury.
... One proposed explanation of these results is that sustaining an injury only increases an individual's future injury risk for a short period of time following the initial injury. 37 The increased risk of injury is possibly only seen while there are deficits in motor control, proprioception, or strength following an initial injury, which may exist for only a few weeks following injury. Athletes who had sustained an injury within the previous six weeks were excluded from our cohort; thus, it is possible we inadvertently excluded athletes who were truly at risk of prospective injury. ...
... Of interest, recent thought suggests a non-linear relationship between factors influencing injury. 37 There are many potential factors that can play a role in an athlete's risk of injury, including motor control, hormones, and the specific time within the season or game. It is possible that these factors, among others, influence the effect of previous injury on future injury. ...
... 38 Because of this, it has been proposed that through targeted rehabilitation aimed at increasing motor control, an athlete can mitigate the detrimental effects of initial injury and ultimately reduce their risk of future injury. 22,37 We acknowledge the presence of limitations in our study. Our small sample size did not allow us to stratify by acute and chronic injuries, which likely have different risk factors. ...
Context:
Temporal prediction of lower extremity (LE) injury risk will benefit clinicians by allowing them to better leverage limited resources and target athletes most at risk.
Objective:
To characterize instantaneous risk of LE injury by demographic factors sex, sport, body mass index (BMI), and previous injury history. Instantaneous injury risk was defined as injury risk at any given point in time following baseline measurement.
Design:
Descriptive epidemiology study.
Setting:
NCAA Division I athletic program.
Patients or other participants:
278 NCAA Division I varsity student-athletes (119 males, 159 females).
Main outcome measure(s):
LE injuries were tracked for 237±235 days. Sex-stratified univariate Cox regression models investigated the association between time to first LE injury and BMI, sport, and previous LE injury history. Relative risk ratios and Kaplan-Meier curves were generated. Variables identified in the univariate analysis were included in a multivariate Cox regression model.
Results:
Females displayed similar instantaneous LE injury risk compared to males (HR=1.29, 95%CI=[0.91,1.83], p=0.16). Overweight athletes (BMI>25 kg/m2) had similar instantaneous LE injury risk compared with athletes with BMI<25 kg/m2 (HR=1.23, 95%CI=[0.84,1.82], p=0.29). Athletes with previous LE injuries were not more likely to sustain subsequent LE injury than athletes with no previous injury (HR=1.09, 95%CI=[0.76,1.54], p=0.64). Basketball (HR=3.12, 95%CI=[1.51,6.44], p=0.002) and soccer (HR=2.78, 95%CI=[1.46,5.31], p=0.002) athletes had higher risk of LE injury than cross-country athletes. In the multivariate model, females were at greater LE injury risk than males (HR=1.55, 95%CI=[1.00,2.39], p=0.05), and males with BMI>25 kg/m2 were at greater risk than all other athletes (HR=0.44, 95%CI=[0.19,1.00], p=0.05).
Conclusions:
In a collegiate athletic population, previous LE injury history was not a significant contributor to risk of future LE injury, while being female or being male with BMI>25 kg/m2 resulted in increased risk of LE injury. Clinicians can use these data to extrapolate LE injury risk occurrence to specific populations.
... In recent years, researchers have attempted to determine the effect of training load on the risk of sports injuries and other sportsrelated health problems. 1 Training load is the physical exertion that the athlete has been exposed to and is a combination of the exposure itself (external load) and the physiological and psychological stressors applied to the athlete in response to the exposure (internal load). 2 Relationships between risk factors and sports injuries are often complex, 3 as the effect of risk factors may depend on the presence or absence of other risk factors, 3 the current state of the athlete, 4 and they may also act non-linearly on the risk of injury. 4 Assessing training load poses additional challenges. ...
... 1 Training load is the physical exertion that the athlete has been exposed to and is a combination of the exposure itself (external load) and the physiological and psychological stressors applied to the athlete in response to the exposure (internal load). 2 Relationships between risk factors and sports injuries are often complex, 3 as the effect of risk factors may depend on the presence or absence of other risk factors, 3 the current state of the athlete, 4 and they may also act non-linearly on the risk of injury. 4 Assessing training load poses additional challenges. 5 6 It is a multidimensional construct that can be measured in multiple ways. ...
Objectives
Determine how to assess the cumulative effect of training load on the risk of injury or health problems in team sports.
Methods
First, we performed a simulation based on a Norwegian Premier League male football dataset (n players=36). Training load was sampled from daily session rating of perceived exertion (sRPE). Different scenarios of the effect of sRPE on injury risk and the effect of relative sRPE on injury risk were simulated. These scenarios assumed that the probability of injury was the result of training load exposures over the previous 4 weeks. We compared seven different methods of modelling training load in their ability to model the simulated relationship. We then used the most accurate method, the distributed lag non-linear model (DLNM), to analyse data from Norwegian youth elite handball players (no. of players=205, no. of health problems=471) to illustrate how assessing the cumulative effect of training load can be done in practice.
Results
DLNM was the only method that accurately modelled the simulated relationships between training load and injury risk. In the handball example, DLNM could show the cumulative effect of training load and how much training load affected health problem risk depending on the distance in time since the training load exposure.
Conclusion
DLNM can be used to assess the cumulative effect of training load on injury risk.
... Given that it is unlikely for one single factor to explain the majority of variance in individual biomechanical differences, our data align with the concept of 'state dependence' recently illuminated in sports medicine research. State dependence postulates that the state of a complex system, whether stable or unstable, dictates the extent to which any given deficit may upset the inherent stability (Stern et al., 2021). For example, the likelihood of a musculoskeletal injury occurring in a female could be dependent upon the state of the motor control system (Hegedus et al., 2016), such that a well-conditioned motor control system may negate the effects of a previous injury or structural anomalies often associated with injuries in females. ...
To examine the isolated and combined effects of sex and perceptual-motor function on single-leg squatting mechanics in males and females. We employed a cross-sectional design in a research laboratory. Fifty-eight females (22.2 ± 3.5 yrs, 1.60 ± .07 m, 64.1 ± 13.0 kg) and 35 males (23.5 ± 5.0 yrs, 1.80 ± .06m, 84.7 ± 15.3 kg) free from time-loss injury in the six months prior, vertigo, and vestibular conditions participated in this study. Independent variables were sex, perceptual-motor metrics (reaction time, efficiency index, conflict discrepancy), and interaction effects. Dependent variables were peak frontal plane angles of knee projection, ipsilateral trunk flexion, and contralateral pelvic drop during single-leg squatting. After accounting for the sex-specific variance and perceptual-motor function effects on frontal plane squatting kinematics, female sex amplified the associations of: higher reaction time, lower efficiency index, and higher conflict discrepancy with greater right ipsilateral peak trunk lean (R2 = .13; p = .05); higher reaction time, lower efficiency index, and higher conflict discrepancy with decreased right contralateral pelvic drop (R2 = .22; p < .001); higher reaction time and lower conflict discrepancy with greater right frontal plane knee projection angle (R2 = .12; p = .03); and higher reaction time with greater left frontal plane knee projection angle (R2 = .22; p < .001). Female sex amplified the relationship between perceptual-motor function and two-dimensional frontal plane squatting kinematics. Future work should determine the extent to which perceptual-motor improvements translate to safer movement strategies.
... In monotonic relationships, the response variable Y (injury probability) moves only in one direction as X (training load) increases, while in non-monotonic relationships, Y sometimes increases and sometimes decreases when X increases. 9 In 2013, Gamble 5 theorised a U-shaped relationship between training load and risk of injury. Data presented by Blanch and Gabbett 6 suggested a J-shaped relationship between ACWR and injury, although the methodology and interpretation of this finding have recently been questioned. ...
Objectives
To determine whether the relationship between training load and injury risk is non-linear and investigate ways of handling non-linearity.
Methods
We analysed daily training load and injury data from three cohorts: Norwegian elite U-19 football (n=81, 55% male, mean age 17 years (SD 1)), Norwegian Premier League football (n=36, 100% male, mean age 26 years (SD 4)) and elite youth handball (n=205, 36% male, mean age 17 years (SD 1)). The relationship between session rating of perceived exertion (sRPE) and probability of injury was estimated with restricted cubic splines in mixed-effects logistic regression models. Simulations were carried out to compare the ability of seven methods to model non-linear relationships, using visualisations, root-mean-squared error and coverage of prediction intervals as performance metrics.
Results
No relationships were identified in the football cohorts; however, a J-shaped relationship was found between sRPE and the probability of injury on the same day for elite youth handball players (p<0.001). In the simulations, the only methods capable of non-linear modelling relationships were the quadratic model, fractional polynomials and restricted cubic splines.
Conclusion
The relationship between training load and injury risk should be assumed to be non-linear. Future research should apply appropriate methods to account for non-linearity, such as fractional polynomials or restricted cubic splines. We propose a guide for which method(s) to use in a range of different situations.
The ability to manipulate pseudospin can find applications in Dirac-material based spintronics. Unlike the transport of real spin that can be modulated by a magnetic field, some form of magnetization, or a spin-transfer torque, pseudospin does not respond to a magnetic field, making modulating pseudospin transport a challenging task. We articulate an asymmetrically coupled cavity-waveguide configuration in graphene and uncover a phenomenon: making the classical dynamics of the cavity deformed can effectively modulate and enhance pseudospin polarization in the waveguide. The underlying mechanism of this remarkable phenomenon can be attributed to chaos-assisted tunneling, which has been well documented in nonrelativistic quantum systems but not yet in Dirac material systems. The finding establishes the feasibility to develop pseudospin modulators for graphene systems through externally applied electrical potential only, with fidelity over 10% at the effective distance of several cavity sizes along the waveguide.
Stability landscapes are useful for understanding the properties of dynamical systems. These landscapes can be calculated from the system’s dynamical equations using the physical concept of scalar potential. Unfortunately, it is well known that for most systems with two or more state variables such potentials do not exist. Here we use an analogy with art to provide an accessible explanation of why this happens and briefly review some of the possible alternatives. Additionally, we introduce a novel and simple computational tool that implements one of those solutions: the decomposition of the differential equations into a gradient term, that has an associated potential, and a non-gradient term, that lacks it. In regions of the state space where the magnitude of the non-gradient term is small compared to the gradient part, we use the gradient term to approximate the potential as quasi-potential. The non-gradient to gradient ratio can be used to estimate the local error introduced by our approximation. Both the algorithm and a ready-to-use implementation in the form of an R package are provided.
Despite the consensus that warming will affect biodiversity, alter physicochemical environments, and disrupt biological interactions, the relative importance of these key processes and how they interact to determine overall ecosystem function is poorly understood. Here, we analyze long-term (16~39 years) time series data from ten aquatic ecosystems and use convergent cross mapping (CCM) to quantify the hidden causal network linking species diversity, ecosystem function, and physicochemical factors. We observe that aquatic ecosystems subject to stronger warming exhibit decreased stability (larger fluctuations in phytoplankton biomass). We further show that this effect can be attributed to a weakening of stabilizing causal pathways between biodiversity, nutrient cycling, and phytoplankton biomass. Thus, rather than thinking in terms of separate factors, a more holistic view, that causally links biodiversity and the other ecosystem components, is required to understand and predict climate impacts on the temporal stability of aquatic ecosystems.
“As ACL injury may alter intracortical facilitation [34] and depressed intracortical inhibition is correlated with decreased quadriceps voluntary activation capability [35], external focus training may provide a means to restore quadriceps muscle activity via increasing intracortical inhibition.
Abstract To control mosquito populations for managing vector-borne diseases, a critical need is to identify and predict their response to causal environmental variables. However, most existing attempts rely on linear approaches based on correlation, which cannot apply in complex, nonlinear natural systems, because correlation is neither a necessary nor sufficient condition for causation. Applying empirical dynamic modelling that acknowledges nonlinear dynamics on nine subpopulations of tiger mosquitos from three neighbouring reef islets of the Raiatea atoll, we identified temperature, precipitation, dew point, air pressure, and mean tide level as causal environmental variables. Interestingly, responses of subpopulations in close proximity (100–500 m) differed with respect to their causal environmental variables and the time delay of effect, highlighting complexity in mosquito-environment causality network. Moreover, we demonstrated how to explore the effects of changing environmental variables on number and strength of mosquito outbreaks, providing a new framework for pest control and disease vector ecology.
Significance
Complex systems in many fields, because of their intrinsic nonlinear dynamics, can exhibit a tipping point (point of no return) at which a total collapse of the system occurs. In ecosystems, environmental deterioration can lead to evolution toward a tipping point. To predict tipping point is an outstanding and extremely challenging problem. Using complex bipartite mutualistic networks, we articulate a dimension reduction strategy and establish its general applicability to predicting tipping points using a large number of empirical networks. Not only can our reduced model serve as a paradigm for understanding the tipping point dynamics in real world ecosystems for safeguarding pollinators, the principle can also be extended to other disciplines to address critical issues, such as resilience and sustainability.
Objective:
To measure the sensitivity and specificity of differences cut-off values for isokinetic Hcon/Qcon ratio in order to improve the capacity to evaluate (retrospectively) the injury of hamstring muscles in professional soccer screened with knee isokinetic tests.
Design:
Retrospective study.
Methods:
Medical and biomechanical data of professional football players playing for the same team for at least one season between 2010 and 2016 were analysed. Hamstring strain injury cases and the reports generated via isokinetic testing were investigated. Isokinetic concentric(con) hamstring(H) and quadriceps(Q) absolute strength in addition with Hcon/Qcon ratio were examined for the injured versus uninjured limbs among injured players, and for the injured and non-injured players. 2 x 2 contingency table was used for comparing variables: predicted injured or predicted uninjured with actual injured or actual uninjured. Sensitivity, specificity, accuracy, positive and negative predictive values, and positive and negative likelihood ratio were calculated for three different cut-off values (0.47 vs. 0.6 vs. 0.658) to compare the discriminative power of an isokinetic test, whilst examining the key value of Hcon/Qcon ratio which may indicate the highest level of ability to predispose a player to injury. McNemar's chi2 test with Yates's correction was used to determine agreement between the tests. PQStat software was used for all statistical analysis, and an alpha level of p <0.05 was used for all statistical comparisons.
Results:
340 isokinetic test reports on both limbs of 66 professional soccer players were analysed. Eleven players suffered hamstring injuries during the analysed period. None of these players sustained recurrence of hamstring injury. One player sustained hamstring strain injury on both legs, thus the total number of injuries was 12. Application of different cut-off values for Hcon/Qcon significantly affected the sensitivity and specificity of isokinetic test used as a tool for muscle injury detection. The use of 0.47 of Hcon/Qcon as a discriminate value resulted in significantly lower sensitivity when compared to 0.658 threshold (sensitivity of 16.7% vs. 91.7%, respectively; t = 6.125,p = 0.0133). Calculated values of specificity (when three different cut-off were applied) were also significantly different. Threshold of 0.6 of Hcon/Qcon resulted with significantly lower specificity compared to 0.47 value (specificity of 46.9% vs. 94.5%, respectively; t = 153.0,p<0.0001), and significantly higher specificity when compared to 0.658 (specificity of 46.9% vs. 24.1%, respectively; t = 229.0, p<0.0001).
Conclusion:
The use of different cut-off values for Hcon/Qcon significantly affected the sensitivity and specificity of isokinetic testing. The interpretation of usefulness of isokinetic test as a screening tool in a group of male professional football players to predict hamstring injury occurrence within the next 12 months might be therefore significantly biased due to the different threshold values of Hcon/Qcon. Using one "normative" value as a cut-off (e.g. 0.47 or 0.60, or 0.658) to quantify soccer players (or not) to the group with a higher risk of knee injury might result in biased outcomes due to the natural strength asymmetry that is observed within the group of soccer players.
A major conceptual step forward in understanding the logical architecture of living systems was advanced by von Neumann with his universal constructor, a physical device capable of self-reproduction. A necessary condition for a universal constructor to exist is that the laws of physics permit physical universality, such that any transformation (consistent with the laws of physics and availability of resources) can be caused to occur. While physical universality has been demonstrated in simple cellular automata models, so far these have not displayed a requisite feature of life—namely open-ended evolution—the explanation of which was also a prime motivator in von Neumann’s formulation of a universal constructor. Current examples of physical universality rely on reversible dynamical laws, whereas it is well-known that living processes are dissipative. Here we show that physical universality and open-ended dynamics should both be possible in irreversible dynamical systems if one entertains the possibility of state-dependent laws. We demonstrate with simple toy models how the accessibility of state space can yield open-ended trajectories, defined as trajectories that do not repeat within the expected Poincaré recurrence time and are not reproducible by an isolated system. We discuss implications for physical universality, or an approximation to it, as a foundational framework for developing a physics for life.
Although it seems obvious that with more data, the predictive capacity of ecological
models should improve, a way to demonstrate this fundamental result has not been so obvious. In
particular, when the standard models themselves are inadequate (von Bertalanffy, extended
Ricker etc.) no additional data will improve performance. By using time series from the Sir Alister
Hardy Foundation for Ocean Science Continuous Plankton Recorder, we demonstrate that longterm
observations reveal both the prevalence of nonlinear processes in species abundances and
an improvement in out-of-sample predictability as the number of observations increase. The
empirical results presented here quantitatively demonstrate the importance of long-term temporal
data collection programs for improving ecosystem models and forecasts, and to better support
environmental management actions.
IntroductionNumerous studies have documented the incidence and nature of injuries in professional rugby union, but few have identified specific risk factors for injury in this population using appropriate statistical methods. In particular, little is known about the role of previous short-term or longer-term match exposures in current injury risk in this setting. Objectives
Our objective was to investigate the influence that match exposure has upon injury risk in rugby union. Method
We conducted a seven-season (2006/7–2012/13) prospective cohort study of time-loss injuries in 1253 English premiership professional players. Players’ 12-month match exposure (number of matches a player was involved in for ≥20 min in the preceding 12 months) and 1-month match exposure (number of full-game equivalent [FGE] matches in preceding 30 days) were assessed as risk factors for injury using a nested frailty model and magnitude-based inferences. ResultsThe 12-month match exposure was associated with injury risk in a non-linear fashion; players who had been involved in fewer than ≈15 or more than ≈35 matches over the preceding 12-month period were more susceptible to injury. Monthly match exposure was linearly associated with injury risk (hazard ratio [HR]: 1.14 per 2 standard deviation [3.2 FGE] increase, 90% confidence interval [CI] 1.08–1.20; likely harmful), although this effect was substantially attenuated for players in the upper quartile for 12-month match exposures (>28 matches). ConclusionA player’s accumulated (12-month) and recent (1-month) match exposure substantially influences their current injury risk. Careful attention should be paid to planning the workloads and monitoring the responses of players involved in: (1) a high (>≈35) number of matches in the previous year, (2) a low (<≈15) number of matches in the previous year, and (3) a low-moderate number of matches in previous year but who have played intensively in the recent past. These findings make a major contribution to evidence-based policy decisions regarding match workload limits in professional rugby union.
Injury prediction is one of the most challenging issues in sports and a key component for injury prevention. Sports injuries aetiology investigations have assumed a reductionist view in which a phenomenon has been simplified into units and analysed as the sum of its basic parts and causality has been seen in a linear and unidirectional way. This reductionist approach relies on correlation and regression analyses and, despite the vast effort to predict sports injuries, it has been limited in its ability to successfully identify predictive factors. The majority of human health conditions are complex. In this sense, the multifactorial complex nature of sports injuries arises not from the linear interaction between isolated and predictive factors, but from the complex interaction among a web of determinants. Thus, the aim of this conceptual paper was to propose a complex system model for sports injuries and to demonstrate how the implementation of complex system thinking may allow us to better address the complex nature of the sports injuries aetiology. According to this model, we should identify features that are hallmarks of complex systems, such as the pattern of relationships (interactions) among determinants, the regularities (profiles) that simultaneously characterise and constrain the phenomenon and the emerging pattern that arises from the complex web of determinants. In sports practice, this emerging pattern may be related to injury occurrence or adaptation. This novel view of preventive intervention relies on the identification of regularities or risk profile, moving from risk factors to risk pattern recognition.
Simultaneous recordings from large neural populations are becoming increasingly common. An important feature of population activity is the trial-to-trial correlated fluctuation of spike train outputs from recorded neuron pairs. Similar to the firing rate of single neurons, correlated activity can be modulated by a number of factors, from changes in arousal and attentional state to learning and task engagement. However, the physiological mechanisms that underlie these changes are not fully understood. We review recent theoretical results that identify three separate mechanisms that modulate spike train correlations: changes in input correlations, internal fluctuations and the transfer function of single neurons. We first examine these mechanisms in feedforward pathways and then show how the same approach can explain the modulation of correlations in recurrent networks. Such mechanistic constraints on the modulation of population activity will be important in statistical analyses of high-dimensional neural data.
Background:
There is dogma that higher training load causes higher injury rates. However, there is also evidence that training has a protective effect against injury. For example, team sport athletes who performed more than 18 weeks of training before sustaining their initial injuries were at reduced risk of sustaining a subsequent injury, while high chronic workloads have been shown to decrease the risk of injury. Second, across a wide range of sports, well-developed physical qualities are associated with a reduced risk of injury. Clearly, for athletes to develop the physical capacities required to provide a protective effect against injury, they must be prepared to train hard. Finally, there is also evidence that under-training may increase injury risk. Collectively, these results emphasise that reductions in workloads may not always be the best approach to protect against injury.
Main thesis:
This paper describes the 'Training-Injury Prevention Paradox' model; a phenomenon whereby athletes accustomed to high training loads have fewer injuries than athletes training at lower workloads. The Model is based on evidence that non-contact injuries are not caused by training per se, but more likely by an inappropriate training programme. Excessive and rapid increases in training loads are likely responsible for a large proportion of non-contact, soft-tissue injuries. If training load is an important determinant of injury, it must be accurately measured up to twice daily and over periods of weeks and months (a season). This paper outlines ways of monitoring training load ('internal' and 'external' loads) and suggests capturing both recent ('acute') training loads and more medium-term ('chronic') training loads to best capture the player's training burden. I describe the critical variable-acute:chronic workload ratio)-as a best practice predictor of training-related injuries. This provides the foundation for interventions to reduce players risk, and thus, time-loss injuries.
Summary:
The appropriately graded prescription of high training loads should improve players' fitness, which in turn may protect against injury, ultimately leading to (1) greater physical outputs and resilience in competition, and (2) a greater proportion of the squad available for selection each week.
BACKGROUND: Prospective studies have reported that abnormal movement patterns at the trunk, hip, and knee are associated with noncontact anterior cruciate ligament (ACL) injuries. Impaired hip strength may underlie these abnormal movement patterns, suggesting that diminished hip strength may increase the risk of noncontact ACL injury.
PURPOSE: To determine whether baseline hip strength predicts future noncontact ACL injury in athletes.
STUDY DESIGN: Case-control study; Level of evidence, 3.
METHODS: Before the start of the competitive season, isometric hip strength (external rotation and abduction) was measured bilaterally by use of a handheld dynamometer in 501 competitive athletes (138 female and 363 male athletes) participating in various sports. During the sport season, ACL injury status was recorded, and injured athletes were further classified based on the mechanism of injury (noncontact vs contact). After the season, logistic regression was used to determine whether baseline hip strength predicted future noncontact ACL injury. Receiver operating characteristic (ROC) curves were constructed independently for each strength measure to determine the clinical cutoff value between a high-risk and low-risk outcome.
RESULTS: A total of 15 noncontact ACL injuries were confirmed (6 females, 9 males), for an overall annual incidence of 3.0% (2.5% for males, 4.3% for females). Baseline hip strength measures (external rotation and abduction) were significantly lower in injured athletes compared with noninjured athletes (P = .003 and P < .001, respectively). Separate logistic regression models indicated that impaired hip strength increased future injury risk (external rotation: odds ratio [OR] = 1.23 [95% CI, 1.08-1.39], P = .001; abduction: OR = 1.12 [95% CI, 1.05-1.20], P = .001). Clinical cutoffs to define high risk were established as external rotation strength ≤20.3% BW (percentage of body weight) or abduction strength ≤35.4% BW.
CONCLUSION: Measures of preseason isometric hip abduction and external rotation strength independently predicted future noncontact ACL injury status in competitive athletes. The study data suggest that screening procedures to assess ACL injury risk should include an assessment of isometric hip abduction and/or external rotation strength.
Background:
Laboratory-based measures provide an accurate method to identify risk factors for anterior cruciate ligament (ACL) injury; however, these methods are generally prohibitive to the wider community. Screening methods that can be completed in a field or clinical setting may be more applicable for wider community use. Examination of field-based screening methods for ACL injury risk can aid in identifying the most applicable method(s) for use in these settings.
Objective:
The objective of this systematic review was to evaluate and compare field-based screening methods for ACL injury risk to determine their efficacy of use in wider community settings.
Data sources:
An electronic database search was conducted on the SPORTDiscus™, MEDLINE, AMED and CINAHL databases (January 1990-July 2015) using a combination of relevant keywords. A secondary search of the same databases, using relevant keywords from identified screening methods, was also undertaken.
Study selection:
Studies identified as potentially relevant were independently examined by two reviewers for inclusion. Where consensus could not be reached, a third reviewer was consulted. Original research articles that examined screening methods for ACL injury risk that could be undertaken outside of a laboratory setting were included for review.
Study appraisal and synthesis methods:
Two reviewers independently assessed the quality of included studies. Included studies were categorized according to the screening method they examined. A description of each screening method, and data pertaining to the ability to prospectively identify ACL injuries, validity and reliability, recommendations for identifying 'at-risk' athletes, equipment and training required to complete screening, time taken to screen athletes, and applicability of the screening method across sports and athletes were extracted from relevant studies.
Results:
Of 1077 citations from the initial search, a total of 25 articles were identified as potentially relevant, with 12 meeting all inclusion/exclusion criteria. From the secondary search, eight further studies met all criteria, resulting in 20 studies being included for review. Five ACL-screening methods-the Landing Error Scoring System (LESS), Clinic-Based Algorithm, Observational Screening of Dynamic Knee Valgus (OSDKV), 2D-Cam Method, and Tuck Jump Assessment-were identified. There was limited evidence supporting the use of field-based screening methods in predicting ACL injuries across a range of populations. Differences relating to the equipment and time required to complete screening methods were identified.
Limitations:
Only screening methods for ACL injury risk were included for review. Field-based screening methods developed for lower-limb injury risk in general may also incorporate, and be useful in, screening for ACL injury risk.
Conclusions:
Limited studies were available relating to the OSDKV and 2D-Cam Method. The LESS showed predictive validity in identifying ACL injuries, however only in a youth athlete population. The LESS also appears practical for community-wide use due to the minimal equipment and set-up/analysis time required. The Clinic-Based Algorithm may have predictive value for ACL injury risk as it identifies athletes who exhibit high frontal plane knee loads during a landing task, but requires extensive additional equipment and time, which may limit its application to wider community settings.
To explore the association between in-season training load measures and injury risk in professional Rugby Union players. Methods This was a one-season prospective cohort study of 173 Professional Rugby Union players from four English Premiership teams. Training load (duration x session-RPE) and time-loss injuries were recorded for all players for all pitch and gym based sessions. Generalised estimating equations were used to model the association between in-season training load measures and injury risk in the subsequent week.
Injury risk increased linearly with one-week loads and week-to-week changes in loads, with a 2 standard deviation (SD) increase in these variables (1245 AU and 1069 AU, respectively) associated with odds ratios of 1.68 (95% CI 1.05-2.68) and 1.58 (95% CI: 0.98-2.54). When compared with the reference group (<3684 AU), a significant non-linear effect was evident for four-week cumulative loads, with a likely beneficial reduction in injury risk associated with intermediate loads of 5932 to 8651 AU (OR: 0.55, 95% CI: 0.22-1.38) (this range equates to around four weeks of average in-season training load), and a likely harmful effect evident for higher loads of >8651 AU (OR: 1.39, 95% CI: 0.98-1.98).
Players had an increased risk of injury if they had high one-week cumulative loads (1245 AU), or large week-to-week changes in load (1069 AU). In addition, a 'U-shaped' relationship was observed for four-week cumulative loads, with an apparent increase in risk associated with higher loads (>8651 AU). These measures should therefore be monitored to inform injury risk reduction strategies.
Soccer has one of the highest incidences of anterior cruciate ligament (ACL) injuries for both males and females. Several injury prevention programs have been developed to address this concern. However, an analysis of the pooled effect has yet to be elicited.
To conduct a systematic review and meta-analysis of ACL and knee injury prevention programs for soccer players, assess the heterogeneity among the studies, and evaluate the reported effectiveness of the prevention programs.
Systematic review and meta-analysis.
A systematic search of the literature was conducted on PubMed (Medline), Embase, CINAHL, and Central-Cochrane Database. Studies were limited to randomized controlled trials (RCTs) of injury prevention programs specific to the knee and/or ACL in soccer players. The Cochrane Q test and I (2) index were independently used to assess heterogeneity among the studies. The pooled risk difference, assessing knee and/or ACL injury rates between intervention and control groups, was calculated by random-effects models with use of the DerSimonian-Laird method. Publication bias was assessed with a funnel plot and Egger weighted regression technique.
Nine studies met the inclusion criteria as RCTs. A total of 11,562 athletes were included, of whom 7889 were analyzed for ACL-specific injuries. Moderate heterogeneity was found among studies of knee injury prevention (P = .041); however, there was insignificant variation found among studies of ACL injury prevention programs (P = .222). For studies of knee injury prevention programs, the risk ratio was 0.74 (95% CI, 0.55-0.89), and a significant reduction in risk of knee injury was found in the prevention group (P = .039). For studies of ACL injury prevention programs, the risk ratio was 0.66 (95% CI, 0.33-1.32), and a nonsignificant reduction in risk of ACL injury was found in the prevention group (P = .238). No evidence of publication bias was found among studies of either knee or ACL injury prevention programs.
This systematic review and meta-analysis of ACL and knee injury prevention program studies found a statistically significant reduction in injury risk for knee injuries but did not find a statistically significant reduction of ACL injuries.
© 2014 The Author(s).
First-order difference equations arise in many contexts in the biological, economic and social sciences. Such equations, even though simple and deterministic, can exhibit a surprising array of dynamical behaviour, from stable points, to a bifurcating hiearchy of stable cycles, to apparently random fluctuations. There are consequently many fascinating problems, some concerned with delicate mathematical aspects of the fine structure of the trajectories, and some concerned with the practical implications and applications. This is an interpretive review of them.
Transient chaos is a common phenomenon in nonlinear dynamics of many physical, biological, and engineering systems. In applications it is often desirable to maintain sustained chaos even in parameter regimes of transient chaos. We address how to sustain transient chaos in deterministic flows. We utilize a simple and practical method, based on extracting the fundamental dynamics from time series, to maintain chaos. The method can result in control of trajectories from almost all initial conditions in the original basin of the chaotic attractor from which transient chaos is created. We apply our method to three problems: (1) voltage collapse in electrical power systems, (2) species preservation in ecology, and (3) elimination of undesirable bursting behavior in a chemical reaction system.
All ecosystems are exposed to gradual changes in climate, nutrient loading, habitat fragmentation or biotic exploitation. Nature is usually assumed to respond to gradual change in a smooth way. However, studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state. Although diverse events can trigger such shifts, recent studies show that a loss of resilience usually paves the way for a switch to an alternative state. This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.
Female athletes participating in high-risk sports suffer anterior cruciate ligament injury at a 4- to 6-fold greater rate than do male athletes.
Prescreened female athletes with subsequent anterior cruciate ligament injury will demonstrate decreased neuromuscular control and increased valgus joint loading, predicting anterior cruciate ligament injury risk.
Cohort study; Level of evidence, 2.
There were 205 female athletes in the high-risk sports of soccer, basketball, and volleyball prospectively measured for neuromuscular control using 3-dimensional kinematics (joint angles) and joint loads using kinetics (joint moments) during a jump-landing task. Analysis of variance as well as linear and logistic regression were used to isolate predictors of risk in athletes who subsequently ruptured the anterior cruciate ligament.
Nine athletes had a confirmed anterior cruciate ligament rupture; these 9 had significantly different knee posture and loading compared to the 196 who did not have anterior cruciate ligament rupture. Knee abduction angle (P<.05) at landing was 8 degrees greater in anterior cruciate ligament-injured than in uninjured athletes. Anterior cruciate ligament-injured athletes had a 2.5 times greater knee abduction moment (P<.001) and 20% higher ground reaction force (P<.05), whereas stance time was 16% shorter; hence, increased motion, force, and moments occurred more quickly. Knee abduction moment predicted anterior cruciate ligament injury status with 73% specificity and 78% sensitivity; dynamic valgus measures showed a predictive r2 of 0.88.
Knee motion and knee loading during a landing task are predictors of anterior cruciate ligament injury risk in female athletes.
Female athletes with increased dynamic valgus and high abduction loads are at increased risk of anterior cruciate ligament injury. The methods developed may be used to monitor neuromuscular control of the knee joint and may help develop simpler measures of neuromuscular control that can be used to direct female athletes to more effective, targeted interventions.
Complex nonlinear dynamics are ubiquitous in marine ecology. Empirical dynamic modelling can be used to infer ecosystem dynamics and species interactions while making minimal assumptions. Although there is growing enthusiasm for applying these methods, the background required to understand them is not typically part of contemporary marine ecology curricula, leading to numerous questions and potential misunderstanding. In this study, we provide a brief overview of empirical dynamic modelling, followed by answers to the ten most frequently asked questions about nonlinear dynamics and nonlinear forecasting.
Acute:chronic workload ratios (ACWRs) are associated with injury risk across team sports. In this study, one season of workload and wellness data from 42 collegiate football players were retrospectively analyzed. Daily 7:21 day exponentially weighted moving average (EWMA) ACWRs were calculated, and z-score fluctuations (“normal,” “better,” and “worse”) in sleep, soreness, energy, and overall wellness were assessed relative to the previous day ACWRs and considered as an interactive effect on the risk of noncontact injury within 0–3 days. Fifty-five noncontact injuries were observed, and injury risks were very likely higher when ACWRs were 2 SDs above (relative risk [RR]: 3.05, 90% confidence interval [CI]: 1.14–8.16) and below (RR: 2.49, 90% CI: 1.11–5.58) the mean. A high ACWR was trivially associated (p < 0.05) with “worse” wellness (r = −0.06, CI: −0.10 to −0.02), muscle soreness (r = −0.07, CI: −0.11 to −0.03), and energy (r = −0.05, CI: −0.09 to −0.01). Feelings of “better” overall wellness and muscle soreness with collectively high EWMA ACWRs displayed likely higher injury risks compared with “normal” (RR: 1.52, 90% CI: 0.91 to 2.54; RR: 1.64, 90% CI: 1.10–2.47) and likely or very likely (RR: 2.36, 90% CI: 0.83 to 674; RR: 2.78, 90% CI: 1.21–6.38) compared with “worse” wellness and soreness, respectively. High EWMA ACWRs increased injury risk and negatively impacted wellness. However, athletes reporting “better” wellness, driven by “better” muscle soreness presented with the highest injury risk when high EWMA ACWRs were observed. This suggests that practitioners are responsive to, and/or athletes are able to self-modulate workload activities.
Purpose:
To examine the extent to which an ACL injury prevention programme modifies lower extremity biomechanics during single- and double-leg landing tasks in both the sagittal and frontal plane. It was hypothesized that the training programme would elicit improvements in lower extremity biomechanics, but that these improvements would be greater during a double-leg sagittal plane landing task than tasks performed on a single leg or in the frontal plane.
Methods:
Ninety-seven competitive multi-directional sport athletes that competed at the middle- or high-school level were cluster randomized into intervention (n = 48, age = 15.4 ± 1.0 years, height = 1.7 ± 0.07 m, mass = 59.9 ± 11.0 kg) and control (n = 49, age = 15.7 ± 1.6 years, height = 1.7 ± 0.06 m, mass = 60.4 ± 7.7 kg) groups. The intervention group participated in an established 6-week warm-up-based ACL injury prevention programme. Three-dimensional biomechanical analyses of a double- (SAG-DL) and single-leg (SAG-SL) sagittal, and double- (FRONT-DL) and single-leg (FRONT-SL) frontal plane jump landing tasks were tested before and after the intervention. Peak angles, excursions, and external joint moments were analysed for group differences using 2 (group) × 4 (task) repeated measures MANOVA models of delta scores (post-pre-test value) (α < 0.05).
Results:
Relative to the control group, no significant biomechanical changes were identified in the intervention group for any of the tasks (n.s.). However, a group by task interaction was identified for knee abduction (λ = 0.80, p = 0.02), such that participants in the intervention group showed relative decreases in knee abduction moments during the SAG-DL compared to the SAG-SL (p = 0.005; d = 0.45, CI = 0.04-0.85) task.
Conclusion:
A 6-week warm-up-based ACL injury prevention programme resulted in no significant biomechanical changes during a variety of multi-directional jump landings. Clinically, future prevention programmes should provide a greater training stimulus (intensity, volume), more specificity to tasks associated with the mechanism of ACL injury (single-leg, non-sagittal plane jump landings), and longer programme duration (> 6 weeks) to elicit meaningful biomechanical changes.
Level of evidence:
I.
Background
Hamstring injuries remain prevalent across a number of professional sports. In football, the incidence has even increased by 4% per year at the Champions League level over the last decade. The role of muscle strength or strength ratios and their association with risk of hamstring injury remain restricted by small sample sizes and inconclusive results.
Purpose
The purpose of this study is to identify risk factors for hamstring injury in professional football players in an adequately powered, prospective cohort study. Using both established (isokinetic) and novel (eccentric hamstring test device) measures of muscle strength, we aimed to investigate the relationship between these strength characteristics over the entire range of motion with risk of hamstring injury.
Methods
All teams (n=18) eligible to compete in the premier football league in Qatar underwent a comprehensive strength assessment during their annual periodic health evaluation at Aspetar Orthopaedic and Sports Medicine Hospital in Doha, Qatar. Variables included isokinetic strength, Nordic hamstring exercise strength and dynamic hamstring: quadriceps ratios.
Results
Of the 413 players included (68.2% of all league players), 66 suffered a hamstring injury over the two seasons. Only isokinetic quadriceps concentric at 300°/s (adjusted for bodyweight) was associated with risk of hamstring injury when considered categorically. Age, body mass and playing position were also associated with risk of hamstring injury. None of the other 23 strength variables examined were found to be associated with hamstring injury.
Conclusion
The clinical value of isolated strength testing is limited, and its use in musculoskeletal screening to predict future hamstring injury is unfounded.
Upper airway muscles subserve many essential for survival orofacial behaviors, including their important role as accessory respiratory muscles. In the face of certain predisposition of craniofacial anatomy, both tonic and phasic inspiratory activation of upper airway muscles is necessary to protect the upper airway against collapse. This protective action is adequate during wakefulness, but fails during sleep which results in recurrent episodes of hypopneas and apneas, a condition known as the obstructive sleep apnea syndrome (OSA). Although OSA is almost exclusively a human disorder, animal models help unveil the basic principles governing the impact of sleep on breathing and upper airway muscle activity. This article discusses the neuroanatomy, neurochemistry, and neurophysiology of the different neuronal systems whose activity changes with sleep-wake states, such as the noradrenergic, serotonergic, cholinergic, orexinergic, histaminergic, GABAergic and glycinergic, and their impact on central respiratory neurons and upper airway motoneurons. Observations of the interactions between sleep-wake states and upper airway muscles in healthy humans and OSA patients are related to findings from animal models with normal upper airway, and various animal models of OSA, including the chronic-intermittent hypoxia model. Using a framework of upper airway motoneurons being under concurrent influence of central respiratory, reflex and state-dependent inputs, different neurotransmitters, and neuropeptides are considered as either causing a sleep-dependent withdrawal of excitation from motoneurons or mediating an active, sleep-related inhibition of motoneurons. Information about the neurochemistry of state-dependent control of upper airway muscles accumulated to date reveals fundamental principles and may help understand and treat OSA. © 2016 American Physiological Society. Compr Physiol 6:1801-1850, 2016.
Harnessing complexity in ecology
Ecology concerns the behavior of complex, dynamic, interconnected systems of populations, communities, and ecosystems over time. Yet ecological time series can be relatively short, owing to practical limits on study duration. Ye and Sugihara introduce an analytical approach called multiview embedding, which harnesses the complexity of short, noisy time series that are common in ecology and other disciplines such as economics. Using examples from published data sets, they show how this approach enhances the tractability of complex data from multiple interacting components and offers a way forward in ecological forecasting.
Science , this issue p. 922
This paper addresses if and how a periodic health examination to screen for risk factors for injury can be used to mitigate injury risk. The key question asked is whether it is possible to use screening tests to identify who is at risk for a sports injury-in order to address the deficit through a targeted intervention programme. The paper demonstrates that to validate a screening test to predict and prevent sports injuries, at least 3 steps are needed. First, a strong relationship needs to be demonstrated in prospective studies between a marker from a screening test and injury risk (step 1). Second, the test properties need to be examined in relevant populations, using appropriate statistical tools (step 2). Unfortunately, there is currently no example of a screening test for sports injuries with adequate test properties. Given the nature of potential screening tests (where test performance is usually measured on a continuous scale from low to high), substantial overlap is to be expected between players with high and low risk of injury. Therefore, although there are a number of tests demonstrating a statistically significant association with injury risk, and therefore help the understanding of causative factors, such tests are unlikely to be able to predict injury with sufficient accuracy. The final step needed is to document that an intervention programme targeting athletes identified as being at high risk through a screening programme is more beneficial than the same intervention programme given to all athletes (step 3). To date, there is no intervention study providing support for screening for injury risk.
Background:
A hamstring strain injury (HSI) has become the most common noncontact injury in soccer. Isokinetic muscle strength deficits are considered a risk factor for HSIs. However, underpowered studies with small sample sizes unable to determine small associations have led to inconclusive results regarding the role of isokinetic strength and strength testing in HSIs.
Purpose:
To examine whether differences in isokinetic strength measures of knee flexion and extension represent risk factors for hamstring injuries in a large cohort of professional soccer players in an adequately powered study design.
Study design:
Cohort study; Level of evidence, 2.
Methods:
A total of 614 professional soccer players from 14 teams underwent isokinetic strength testing during preseason screening. Testing consisted of concentric knee flexion and extension at 60 deg/s and 300 deg/s and eccentric knee extension at 60 deg/s. A clustered multiple logistic regression analysis was used to identify variables associated with the risk of HSIs. Receiver operating characteristic (ROC) curves were calculated to determine sensitivity and specificity.
Results:
Of the 614 players, 190 suffered an HSI during the 4 seasons. Quadriceps concentric strength at 60 deg/s (odds ratio [OR], 1.41; 95% CI, 1.03-1.92; P = .03) and hamstring eccentric strength at 60 deg/s (OR, 1.37; 95% CI, 1.01-1.85; P = .04) adjusted for bodyweight were independently associated with the risk of injuries. The absolute differences between the injured and uninjured players were 6.9 N·m and 9.1 N·m, with small effect sizes (d < 0.2). The ROC analyses showed an area under the curve of 0.54 and 0.56 for quadriceps concentric strength and hamstring eccentric strength, respectively, indicating a failed combined sensitivity and specificity of the 2 strength variables identified in the logistic regression models.
Conclusion:
This study identified small absolute strength differences and a wide overlap of the absolute strength measurements at the group level. The small associations between lower hamstring eccentric strength and lower quadriceps concentric strength with HSIs can only be considered as weak risk factors. The identification of these risk factors still does not allow the identification of individual players at risk. The use of isokinetic testing to determine the association between strength differences and HSIs is not supported.
Objective:
We propose a novel paradigm to predict acute attacks and exacerbations in chronic episodic disorders such as asthma, cardiac arrhythmias, migraine, epilepsy, and depression. A better generic understanding of acute transitions in chronic dynamic diseases is increasingly important in critical care medicine because of the higher prevalence and incidence of these chronic diseases in our aging societies.
Data sources:
PubMed, Medline, and Web of Science.
Study selection:
We selected studies from biology and medicine providing evidence of slowing down after a perturbation as a warning signal for critical transitions.
Data extraction:
Recent work in ecology, climate, and systems biology has shown that slowing down of recovery upon perturbations can indicate loss of resilience across complex, nonlinear biologic systems that are approaching a tipping point. This observation is supported by the empiric studies in pathophysiology and controlled laboratory experiments with other living systems, which can flip from one state of clinical balance to a contrasting one. We discuss examples of such evidence in bodily functions such as blood pressure, heart rate, mood, and respiratory regulation when a tipping point for a transition is near.
Conclusions:
We hypothesize that in a range of chronic episodic diseases, indicators of critical slowing down, such as rising variance and temporal correlation, may be used to assess the risk of attacks, exacerbations, and even mortality. Identification of such early warning signals over a range of diseases will enhance the understanding of why, how, and when attacks and exacerbations will strike and may thus improve disease management in critical care medicine.
Background The ability to predict injury is difficult. Prior injury is the only risk factor that has been reported consistently in multiple research studies. Convenient and easy to perform, physical performance tests (PPTs) have great allure as prognostic factors.
Methods 11 PPTs were issued to 359 participants over the course of three seasons of National Collegiate Athletic Association Division I athletic competition. Injuries were monitored and reported in a centralised university tracking system. Exploratory factor analysis was performed in order to group the PPTs into constructs. The relationship between injury and these PPT-based constructs and other known predictors of injury was explored using univariate and multivariate regression.
Results PPTs clustered into five constructs: (1) active motion, (2) power, (3) hip stability, (4) flexibility and (5) motor control. When these five were placed into a multiple regression equation along with known risk factors (age, body mass index (BMI), gender, excessive flexibility and past injury), hip stability and active motion were predicted injury. In addition, motor control predicted non-traumatic injury. Past injury did not predict injury in the multivariate model.
Summary In college athletes, hip stability, active motion and motor control as assessed through PPTs can be useful as part of preseason screening. These PPT-related constructs seem to have a mediating effect on the relationship between past injury and future injury. This study provides the rationale to test targeted interventions to address these limitations.
Clinical trial registration number NCT01804894.
We determined the validity of current medical advice to avoid grapefruit juice consumption while taking three widely used statins.(1-3) A daily glass of grapefruit juice increases blood levels of simvastatin and lovastatin by about 260% if taken at the same time, (about 90% if taken 12 hours apart), and atorvastatin by about 80% (whenever taken). Simvastatin 40mg, lovastatin 40mg, and atorvastatin 10mg daily reduce LDL cholesterol levels in a 60 year old man with an LDL cholesterol of 4.8 mmol/l by 37%, reducing ischaemic heart disease risk by 61%. When simvastatin or lovastatin are taken at the same time as grapefruit juice, the estimated reduction in LDL cholesterol is 48% and in heart disease is 70%. If the juice is taken 12 hours before these statins, the reductions are, respectively, 43% and 66%, and for atorvastatin 42% and 66%. The increased rhabdomyolysis risk from grapefruit juice consumption due to the increased effective statin dose is minimal compared with the greater effect in preventing heart disease. Grapefruit juice should not be contraindicated in people taking statins.
Copyright © 2015 Elsevier Inc. All rights reserved.
A state-dependent dynamic system is one in which (1) the marginal effect of x on y at time t () depends on the prior value of the dependent variable , and (2) the persistence of the dependent variable () depends on xt. We present a methodological strategy for dealing with state-dependent dynamic systems and demonstrate the consequences of
ignoring state-dependence. As an applied example, we find evidence of state-dependence in the relationship between presidential
approval and economic performance: high unemployment rates are most damaging to presidential approval among presidents with
the highest initial approval ratings.
For many marine species and habitats, climate change and overfishing present a double threat. To manage marine resources effectively, it is necessary to adapt management to changes in the physical environment. Simple relationships between environmental conditions and fish abundance have long been used in both fisheries and fishery management. In many cases, however, physical, biological, and human variables feed back on each other. For these systems, associations between variables can change as the system evolves in time. This can obscure relationships between population dynamics and environmental variability, undermining our ability to forecast changes in populations tied to physical processes. Here we present a methodology for identifying physical forcing variables based on nonlinear forecasting and show how the method provides a predictive understanding of the influence of physical forcing on Pacific sardine.
Our research group discovered the interaction between grapefruit and certain medications more than 20 years ago.1–3 Currently, more than 85 drugs, most of which are available in Canada, are known or predicted to interact with grapefruit. This interaction enhances systemic drug concentration through impaired drug metabolism.
This article outlines principles relating to the assessment of risk factors and causation in sport injury. The limitations of a univariate exploration of risk factors are outlined, and a new model that permits the assessment of multiple risk factors is proposed. Applying this multivariate model may lead to greater success in predicting athletic injuries and help guide effective prevention strategies.
(C) Lippincott-Raven Publishers.
Cause or Correlation?
Three centuries ago, Bishop Berkeley's 1710 classic “A treatise on the nature of human knowledge,” first spelled out the “correlation vs. causation” dilemma. Sugihara et al. (p. 496 , published online 20 September) present an approach to this conundrum, and extend current discussions about causation to dynamic systems with weak to moderate coupling (such as ecosystems). The resulting method, convergent cross mapping can detect causal linkages between time series.
Nonlinear analyses of infant heart rhythms reveal a marked rise in the complexity of the electrocardiogram with maturation. We find that normal mature infants (gestation greater than or equal to 35 weeks) have complex and distinctly nonlinear heart rhythms (consistent with recent reports for healthy adults) but that such nonlinearity is lacking in preterm infants (gestation > or = to 27 weeks) where parasympathetic-sympathetic interaction and function are presumed to be less well developed. Our study further shows that infants with clinical brain death and those treated with atropine exhibit a similar lack of nonlinear feedback control. These three lines of evidence support the hypothesis championed by Goldberger et al. [Goldberger, A.L., Rigney, D.R. & West, B.J. (1990) Sci. Am. 262, 43-49] that autonomic nervous system control underlies the nonlinearity and possible chaos of normal heart rhythms. This report demonstrates the acquisition of nonlinear heart rate dynamics and possible chaos in developing human infants and its loss in brain death and with the administration of atropine. It parallels earlier work documenting changes in the variability of heart rhythms in each of these cases and suggests that nonlinearity may provide additional power in characterizing physiological states.
We investigate the dynamics of a model of electrically coupled pacemaking cardiac sino-artial node cells. Cell models are biophysically detailed, and include voltage-dependent membrane currents, pump-exchanger currents, and time-varying internal ion concentration changes similar to those seen in real sino-atrial node cells. It is found that at low, yet physiologically realistic coupling conductance values, complex dynamics including chaos can arise. Occurrence of these complex dynamics in coupled pacemaker cells may provide an explanation for the origin of certain cardiac arrhythmias.
Previous studies among young pitchers have focused on the frequency and description of elbow injuries. The purpose of this study was to evaluate the frequency of elbow and shoulder complaints in young pitchers and to identify the associations between pitch types, pitch volume, and other risk factors for these conditions.
A prospective cohort study of 298 youth pitchers was conducted over two seasons. Each participant was contacted via telephone after each game pitched to identify arm complaints. Generalized estimating equations were used to assess associations between arm complaints and independent variables.
The frequency of elbow pain was 26%; that of shoulder pain, 32%. Risk factors for elbow pain were increased age, increased weight, decreased height, lifting weights during the season, playing baseball outside the league, decreased self-satisfaction, arm fatigue during the game pitched, and throwing fewer than 300 or more than 600 pitches during the season. Risk factors for shoulder pain included decreased satisfaction, arm fatigue during the game pitched, throwing more than 75 pitches in a game, and throwing fewer than 300 pitches during the season.
Arm complaints are common, with nearly half of the subjects reporting pain. The factors associated with elbow and shoulder pain were different, suggesting differing etiologies. Developmental factors may be important in both. To lower the risk of pain at both locations, young pitchers probably should not throw more than 75 pitches in a game. Other recommendations are to remove pitchers from a game if they demonstrate arm fatigue and limit pitching in nonleague games.
This study examined the relationship between the bowling workload of first-class cricket fast bowlers and injury with the aim of identifying a workload threshold at which point the risk of injury increases. Ninety male fast bowlers (mean age 27 years, range 18-38 years) from six Australian state squads were observed for the 2000-2001 and/or 2001-2002 cricket seasons. Workload was quantified by examining fixture scorecards and conducting surveillance at training sessions. Injury data was obtained from the Cricket Australia's Injury Surveillance System. Compared to bowlers with an average of 3-3.99 days between bowling sessions, bowlers with an average of less than 2 days (risk ratio (RR) = 2.4, 95% confidence interval (CI) 1.6 to 3.5) or 5 or more days between sessions (RR = 1.8, 95% CI 1.1 to 2.9) were at a significantly increased risk of injury. Compared to those bowlers with an average of 123-188 deliveries per week, bowlers with an average of fewer than 123 deliveries per week (RR = 1.4, 95% CI 1.0 to 2.0) or more than 188 deliveries per week (RR= 1.4, 95% CI 0.9 to 1.6) may also be at an increased risk of injury. There appears to be a dual fast bowling workload threshold beyond which the risk of injury increases and maintaining a workload that is too low or infrequent is an equally significant risk factor for injury as maintaining a high bowling workload. Further study is required to determine the reason why players who bowl infrequently suffer more injuries.
A comprehensive strength testing protocol offers no clinical value in predicting risk of hamstring injury: A prospective cohort study of 413 professional football players
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Long-term warming weakens stabilizing effects of biodiversity in aquatic ecosystems
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