From microscopic to macroscopic sports injuries. Applying the complex dynamic systems approach to sports medicine: a narrative review

Critical Fluctuations as an Early Warning Signal of Sports Injuries? A Proof of Concept Using Football Monitoring Data

BACKGROUND

There has been an increasing interest in the development and prevention of sports injuries from a complex dynamic systems perspective. From this perspective, injuries may occur following critical fluctuations in the psychophysiological state of an athlete. Our objective was to quantify these so-called Early Warning Signals (EWS) as a proof of concept to determine their explanatory performance for injuries. The sample consisted of 23 professional youth football (soccer) players. Self-reports of psychological and physiological factors as well as data from heart rate and GPS sensors were gathered on every training and match day over two competitive seasons, which resulted in an average of 339 observations per player (range = 155-430). We calculated the Dynamic Complexity (DC) index of these data, representing a metric of critical fluctuations. Next, we used this EWS to predict injuries (traumatic and overuse).

RESULTS

Results showed a significant peak of DC in 30% of the incurred injuries, in the six data points (roughly one and a half weeks) before the injury. The warning signal exhibited a specificity of 95%, that is, correctly classifying non-injury instances. We followed up on this promising result with additional calculations to account for the naturally imbalanced data (fewer injuries than non-injuries). The relatively low F1 we obtained (0.08) suggests that the model's overall ability to discriminate between injuries and non-injuries is rather poor, due to the high false positive rate.

CONCLUSION

By detecting critical fluctuations preceding one-third of the injuries, this study provided support for the complex systems theory of injuries. Furthermore, it suggests that increasing critical fluctuations may be seen as an EWS on which practitioners can intervene. Yet, the relatively high false positive rate on the entire data set, including periods without injuries, suggests critical fluctuations may also precede transitions to other (e.g., stronger) states. Future research should therefore dig deeper into the meaning of critical fluctuations in the psychophysiological states of athletes.

KEY POINTS

Complex Systems Theory suggests that sports injuries may be preceded by a warning signal characterized by a short window of increased critical fluctuations. Results of the current study showed such increased critical fluctuations before 30% of the injuries. Across the entire data set, we also found a considerable number of critical fluctuations that were not followed by an injury, suggesting that the warning signal may also precede transitions to other (e.g., healthier) states. Increased critical fluctuations may be interpreted as a window of opportunity for the practitioner to launch timely and targeted interventions, and researchers should dig deeper into the meaning of such fluctuations.

On Leveraging Machine Learning in Sport Science in the Hypothetico-deductive Framework

Supervised machine learning (ML) offers an exciting suite of algorithms that could benefit research in sport science. In principle, supervised ML approaches were designed for pure prediction, as opposed to explanation, leading to a rise in powerful, but opaque, algorithms. Recently, two subdomains of ML-explainable ML, which allows us to "peek into the black box," and interpretable ML, which encourages using algorithms that are inherently interpretable-have grown in popularity. The increased transparency of these powerful ML algorithms may provide considerable support for the hypothetico-deductive framework, in which hypotheses are generated from prior beliefs and theory, and are assessed against data collected specifically to test that hypothesis. However, this paper shows why ML algorithms are fundamentally different from statistical methods, even when using explainable or interpretable approaches. Translating potential insights from supervised ML algorithms, while in many cases seemingly straightforward, can have unanticipated challenges. While supervised ML cannot be used to replace statistical methods, we propose ways in which the sport sciences community can take advantage of supervised ML in the hypothetico-deductive framework. In this manuscript we argue that supervised machine learning can and should augment our exploratory investigations in sport science, but that leveraging potential insights from supervised ML algorithms should be undertaken with caution. We justify our position through a careful examination of supervised machine learning, and provide a useful analogy to help elucidate our findings. Three case studies are provided to demonstrate how supervised machine learning can be integrated into exploratory analysis. Supervised machine learning should be integrated into the scientific workflow with requisite caution. The approaches described in this paper provide ways to safely leverage the strengths of machine learning-like the flexibility ML algorithms can provide for fitting complex patterns-while avoiding potential pitfalls-at best, like wasted effort and money, and at worst, like misguided clinical recommendations-that may arise when trying to integrate findings from ML algorithms into domain knowledge. KEY POINTS: Some supervised machine learning algorithms and statistical models are used to solve the same problem, y = f(x) + ε, but differ fundamentally in motivation and approach. The hypothetico-deductive framework-in which hypotheses are generated from prior beliefs and theory, and are assessed against data collected specifically to test that hypothesis-is one of the core frameworks comprising the scientific method. In the hypothetico-deductive framework, supervised machine learning can be used in an exploratory capacity. However, it cannot replace the use of statistical methods, even as explainable and interpretable machine learning methods become increasingly popular. Improper use of supervised machine learning in the hypothetico-deductive framework is tantamount to p-value hacking in statistical methods.

3-Dimensional Biomechanics of Noncontact Anterior Cruciate Ligament Injuries in Male Professional Soccer Players

BACKGROUND

The understanding of noncontact anterior cruciate ligament (ACL) injury causation in soccer has improved over the past decades. Bidimensional video analyses have significantly augmented our awareness, representing to date the only practical method to describe injury biomechanics. However, the extent of the problem continues to raise serious concerns.

PURPOSE

To advance our understanding of the causal pathways leading to ACL injury with a large-scale reconstruction of 3-dimensional (3D) whole-body joint kinematics of injuries that occurred to male elite soccer players, as well as to compare the joint angle time course among situational patterns.

STUDY DESIGN

Descriptive laboratory study.

METHODS

A total of 33 consecutive noncontact and indirect contact ACL injuries that occurred in 6 national and 2 international professional leagues (seasons 2020-2021 to 2022-2023 until December 2022) were analyzed: (1) multiview noncoaxial television images were inspected; (2) multiple camera views were taken from 400 ms before the initial ground contact to 200 ms after the injury frame; (3) a size-matched pitch was modeled and used to calibrate cameras; (4) a 3D skeletal model was adjusted to fit the player's pose in each frame/view; and (5) poses were interpolated, and Euler joint angles were extracted.

RESULTS

The authors reconstructed the 3D lower limb joint kinematic curves preceding and during ACL injuries in 33 cases; notably, a sudden external (up to 5°) and then internal knee rotation was observed after the initial contact and before the injury frame. The overall kinematics at injury were knee moderately flexed (45.9°± 21.7°), abducted (4.3°± 5.1°), and externally rotated (3.0°± 6.4°); trunk shallowly flexed (17.4°± 12.5°) and rotated and tilted toward the injured side; and hip flexed (32.0°± 18.7°), abducted (31.1°± 12.0°), and slightly internally rotated (6.6°± 12.2°). Variable behaviors were observed at the ankle level.

CONCLUSION

Via reconstruction of the sequence of whole-body joint motion leading to injury, we confirmed the accepted gross biomechanics (dynamic valgus trend). This study significantly enriches the current knowledge on multiplanar kinematic features (transverse and coronal plane rotations). Furthermore, it was shown that ACL injuries in male professional soccer players manifest through distinct biomechanical footprints related to the concurrent game situation.

CLINICAL RELEVANCE

Interventions aimed at reducing ACL injuries in soccer should consider that environmental features (ie, situational patterns) affect injury mechanics.

Kinematics but not kinetics alterations to single-leg drop jump movements following a subject-tailored fatiguing protocol suggest an increased risk of ACL injury

Introduction

Neuromuscular fatigue causes a transient reduction of muscle force, and alters the mechanisms of motor control. Whether these alterations increase the risk of anterior cruciate ligament (ACL) injury is still debated. Here we compare the biomechanics of single-leg drop jumps before and after the execution of a fatiguing exercise, evaluating whether this exercise causes biomechanical alterations typically associated with an increased risk of ACL lesion. The intensity of the fatiguing protocol was tailored to the aerobic capacity of each participant, minimizing potential differential effects due to inter-individual variability in fitness.

Methods

Twenty-four healthy male volunteers performed single leg drop jumps, before and after a single-set fatiguing session on a cycle ergometer until exhaustion (cadence: 65-70 revolutions per minute). For each participant, the intensity of the fatiguing exercise was set to 110% of the power achieved at their anaerobic threshold, previously identified by means of a cardiopulmonary exercise test. Joint angles and moments, as well as ground reaction forces (GRF) before and after the fatiguing exercise were compared for both the dominant and the non-dominant leg.

Results

Following the fatiguing exercise, the hip joint was more extended (landing: Δ=-2.17°, p = 0.005; propulsion: Δ=-1.83°, p = 0.032) and more abducted (landing: Δ=-0.72°, p = 0.01; propulsion: Δ=-1.12°, p = 0.009). Similarly, the knee joint was more extended at landing (non-dominant leg: Δ=-2.67°, p < 0.001; dominant: Δ=-1.4°, p = 0.023), and more abducted at propulsion (both legs: Δ=-0.99°, p < 0.001) and stabilization (both legs: Δ=-1.71°, p < 0.001) hence increasing knee valgus. Fatigue also caused a significant reduction of vertical GRF upon landing (Δ=-0.21 N/kg, p = 0.003), but not during propulsion. Fatigue did not affect joint moments significantly.

Conclusion

The increased hip and knee extension, as well as the increased knee abduction we observed after the execution of the fatiguing exercise have been previously identified as risk factors for ACL injury. These results therefore suggest an increased risk of ACL injury after the execution of the participant-tailored fatiguing protocol proposed here. However, the reduced vertical GRF upon landing and the preservation of joint moments are intriguing, as they may suggest the adoption of protective strategies in the fatigued condition to be evaluated in future studied.

Overuse injury and affects in competitive sport: A prospective longitudinal study

Overuse injuries, which have a high prevalence in sport, are suggested to result in different affective responses in comparison to traumatic injuries. Affects may also reciprocally act as risk factors for overuse injury. The aim of this study was to examine the associations between overuse injury and affects within a longitudinal follow-up design. Competitive athletes (N = 149) of various sports and levels of competition completed the Positive and Negative Affect Schedule (PANAS) and the Oslo Sports Trauma Research Centre Overuse injury questionnaire (OSTRC-O) once a week over 10 consecutive weeks. Bivariate unconditional latent curve model analyses with structured residuals were performed to evaluate the associations within and across weeks between OSTRC-O severity score and affects. Results indicated that OSTRC-O severity score and positive affects (PA) had a statistically significant negative within-week relation (r = -24.51, 95% CI = [-33.9, -15.1], p < 0.001). Higher scores of overuse injury were significantly related to lower levels of PA across weeks (ß = -0.02, 95% CI = [-0.04, -0.001], p = 0.044), while the reciprocal effect of PA on overuse injury was not significant (ß = -0.13, 95% CI = [-0.52, 0.26], p = 0.51). No statistically significant association was observed between OSTRC-O severity score and negative affects, neither within nor across weeks. Our findings suggest that overuse injury may have adverse psychological consequences on the long run through lessened PA and address the need for providing sustainable psychological support focusing upon such PA when working with athletes experiencing overuse injury.

Metabolic, cognitive and neuromuscular responses to different multidirectional agility-like sprint protocols in elite female soccer players - a randomised crossover study

PURPOSE

Resistance to fatigue is a key factor in injury prevention that needs to be considered in return-to-sport (RTS) scenarios, especially after severe knee ligament injuries. Fatigue should be induced under game-like conditions. The SpeedCourt (SC) is a movement platform for assessing multidirectional sprint performance, typical of game-sports, due to change-of-direction movements in response to a visual stimulus. Designing adequate fatigue protocols requires the suitable arrangement of several loading variables such as number of intervals, sprint distance or work/relief ratio (W:R). Therefore, this study analysed the acute fatigue effects of different SC protocols on metabolic load, cognitive function and neuromuscular performance.

METHODS

Eighteen female soccer players (mean ± SD; age: 23.1 ± 4.6 years) of the 1st German Division participated in this randomised, crossover study. Using a random allocation sequence, players completed four volume-equated protocols differing in W:R and sprint distance per interval (P1:12 × 30 m, W:R = 1:2 s; P2:12 × 30 m, W:R = 1:3 s; P3:18 × 20 m, W:R = 1:2 s; P4:18 × 20 m, W:R = 1:3 s). Pre- and post-exercise, metabolic load was measured per blood lactate concentration (BLaC), cognitive function per reaction time (RT), and neuromuscular performance including multiple rebound jumps (MRJ height, primary outcome variable; Reactive Strength Index, RSI) and 5 m sprint times (SP5).

RESULTS

Repeated-measures ANOVA revealed significant main time effects (p < .05) with improved performance post-exercise in RT (504 vs. 482 ms, d = 1.95), MRJ height (24.0 vs. 24.8 cm, d = 0.77), RSI (1.39 vs. 1.43, d = 0.52), and SP5 (1.19 vs. 1.17 s, d = 0.56). There was significant main time (p < .001) and time x protocol interaction effects in BLaC (p < .001). P1 induced higher BLaC values (4.52 ± 1.83 mmol/L) compared to P2 (3.79 ± 1.83 mmol/L; d = 0.74) and P4 (3.12 ± 1.83 mmol/L; d = 1.06), whereas P3 (4.23 ± 1.69 mmol/L) elicited higher BLaC values compared to P4 (d = 0.74).

CONCLUSION

All protocols caused an improved cognitive function and neuromuscular performance. The former may be related to enhanced noradrenergic activation or exercise specificity which induced an improved stimulus processing. The latter may be explained by a possible post-activation performance enhancement effect on jump and sprint performance. A shorter relief duration in W:R as opposed to sprint distance per interval produced higher BLaC values. The protocols may serve as reference data for improved RTS decision-making in elite female soccer players.

TRIAL REGISTRATION

Deutsches Register Klinischer Studien (DRKS), No.: DRKS00033496 , Registered 19. Februar 2024, Retrospectively Registered.

Prevalence of and Factors Associated with Sports Injuries in 11,000 Japanese Collegiate Athletes

BACKGROUND

To establish the 1-year prevalence of sports injuries and explore associations of various factors with a sports injury in Japanese collegiate athletes.

METHODS

The data were collected through a web-based survey of Japanese collegiate athletes associated with UNIVAS (Japan Association for University Athletics and Sport). The survey questions asked about athletes' personal characteristics, sports participation, and injuries sustained within the previous year. Follow-up questions on the details regarding the three most serious injuries were asked. Differences in proportions of athlete characteristics between males and females and between injured and uninjured were explored with the chi-square test. Factors associated with sustaining an injury were determined with regression analysis.

RESULTS

The prevalence of injuries among Japanese collegiate athletes is high, and most of the sustained injuries require athletes to take a considerable time off training and competition indicating their severity. Athletes from year two and higher at the university, overweight or obese, training more often per week, and with longer sports experience were more likely to sustain an injury within the previous year.

CONCLUSIONS

There is compelling evidence to suggest that excessive training and insufficient recovery may be contributing to their increased risk of injury. These findings underscore the importance of implementing evidence-based training programs and recovery strategies to mitigate injury risk and optimize performance outcomes among this population.

Changes in neuromuscular activation, heart rate and rate of perceived exertion over the course of a wheelchair propulsion fatigue protocol

Shoulder pain is common in persons with spinal cord injury and has been associated with wheelchair use. Fatigue related compensation strategies have been identified as possibly impacting the development of shoulder injury and pain. The purpose of this study was to investigate the progression of performance fatigability (i.e., decline in objective measure of performance including neuromuscular activation and increase in heart rate) and perceived fatigability (i.e., increased perceived exertion) during a 15-min fatigue protocol including maximum voluntary overground wheelchair propulsion. Fifty participants with paraplegic spinal cord injury completed three 4-min rounds of wheelchair propulsion, separated by 90 s of rest, on a figure-8 course consisting of two turns and full stops per lap in their manual wheelchairs (ClinicalTrials.gov: NCT03153033). Electromyography (EMG) signal of five muscles acting on the shoulder joint, heart rate (HR), and rate of perceived exertion (RPE) were measured at the beginning and end of every 4 min of propulsion. Root Mean Square (RMS) and Mean Power Frequency were calculated from EMG data. There was a significant increase in %RMS of the pectoralis major pars sternalis and trapezius pars descendens, HR, and RPE with greatest changes during the first 4 min of the protocol. The observed changes in neuromuscular activation in only two of the shoulder muscles may impact muscular imbalances and the development of shoulder injuries and should be further studied. The current study gives clearer insight into the mechanisms of performance fatigability and perceived fatigability throughout a wheelchair propulsion fatigue protocol.

Understanding Training Load as Exposure and Dose

Various terms used in sport and exercise science, and medicine, are derived from other fields such as epidemiology, pharmacology and causal inference. Conceptual and nomological frameworks have described training load as a multidimensional construct manifested by two causally related subdimensions: external and internal training load. In this article, we explain how the concepts of training load and its subdimensions can be aligned to classifications used in occupational medicine and epidemiology, where exposure can also be differentiated into external and internal dose. The meanings of terms used in epidemiology such as exposure, external dose, internal dose and dose-response are therefore explored from a causal perspective and their underlying concepts are contextualised to the physical training process. We also explain how these concepts can assist in the validation process of training load measures. Specifically, to optimise training (i.e. within a causal context), a measure of exposure should be reflective of the mediating mechanisms of the primary outcome. Additionally, understanding the difference between intermediate and surrogate outcomes allows for the correct investigation of the effects of exposure measures and their interpretation in research and applied settings. Finally, whilst the dose-response relationship can provide evidence of the validity of a measure, conceptual and computational differentiation between causal (explanatory) and non-causal (descriptive and predictive) dose-response relationships is needed. Regardless of how sophisticated or "advanced" a training load measure (and metric) appears, in a causal context, if it cannot be connected to a plausible mediator of a relevant response (outcome), it is likely of little use in practice to support and optimise the training process.

Starters and non-starters soccer players in competition: is physical performance increased by the substitutions?

BACKGROUND

Non-starters soccer players have a great role within the team, being indispensable to reduce fatigue, as well as to maintain and increase the team's performance during the match.

OBJECTIVE

This study aimed to analyze the physical performance of the starter and non-starters players during competitive soccer matches.

METHODS

Twenty-two soccer players participated in this study, divided into two groups according to the role in the match (starters or non-starters). WIMU Global Positioning System devices were used in order to record physical performance metrics. Independent samples t-test and one-way ANOVA tests were performed to compare starters and non-starters, and the playing position, respectively, and two-way ANOVA test was perform with these factors too.

RESULTS

There were no differences in the main physical performance metrics between starters and non-starters players during competition, although there were differences in physical performance metrics according to the playing position. Midfielders performed highest distance per minute, player load, and distance covered between 12 and 21 km·h^- 1 (p < .05). Finally, distance covered at speeds greater than 24 km·h^- 1 was predicted by the playing role (starters and non-starters) and playing position factors with 88% of explained variance (η_p² = 0.772).

CONCLUSION

The main findings of this study showed that non-starter players had a similar physical performance during competitive matches as the starter players for whom they are substituted. In addition, the playing position determined different physical performance, contributing in this manuscript that behavior and decision-making of the players could be affected by their position in the field. More studies are needed on non-starter player performance and contextual factors that could influence the physical responses of these players.

Assessing proprioception through time-variability properties of acceleration

Proprioception is a crucial property for movement stability and balance, but its current assessment, based on clinical testing, lacks precision and adequacy in real contexts. This study proposes assessing proprioception and its sensitivity to training effects through acceleration time series recorded during two slackline experiments. In the first experiment, slackliners of different expertise (highly and poorly trained) had to walk on a slackline for 30 s. In the second, twelve beginners had to balance up on the slackline for at least 11 s before and after a training process. Acceleration time series were recorded in body components (legs and centre of mass) and the slackline. The acceleration fluctuations were analysed through Detrended Fluctuation Analysis. The obtained Hurst (H)-exponents were compared between both groups (first experiment) and before and after training (second experiment) using Whitney and Wilcoxon tests, respectively. The values of H-exponents were lower in the highly trained group (Z = -2.15, p = 0.03) (first experiment), and in the post-training conditions (Z = -2.35, p = 0.02) (second experiment). These results suggest better motor and proprioceptive control with training status. Hence, the time-variability structure of acceleration in real contexts, like slackline tasks, is proposed as an objective measure of proprioception and its training effects.

NURSING IN SPORTS ANKLE INJURY BASED ON THE FITNESS EXERCISE

ABSTRACT Introduction Ankle injury is an acute soft tissue pathology where the ankle ligaments are distended, lacerated, or ruptured due to violence during sport. This joint is also one of the most vulnerable in sports. After an injury, immediate and adequate care is significant in reducing pain and complication. Objective Statistically analyze the sports injuries of the ankle cases, determining the principal reasons for injury and outlining preventive measures. Methods A statistical investigation on the sports injuries of 275 Qiqihar higher education students was performed with questionnaires and teaching practice methods. The research was focused on the injured structures and the injury causes analysis. In parallel, corresponding proposals aimed at preventing these sports injuries were raised. Results Joint injuries and ankle sprains followed by hematomas represented the most significant proportion of ankle injuries. The reasons are lack of physical fitness, lack of awareness of self-protection, inadequate preparation in the sporting environment facilities, and performing tasks outside what the superior specified was specified. Conclusion Medical work needs to increase dissemination so that people realize the causes of sports injuries. At the same time, it helps people master the care measures before and after the injury. This reduces the incidence of sports injuries and reduces the occurrence of complications. Evidence level II; Therapeutic Studies - Investigating the results.

EXERCISE FATIGUE INJURY UNDER SPORT RESISTANCE

ABSTRACT Introduction Athletes are prone to local muscle fatigue due to high-intensity training and to long-term accumulation of musculoskeletal injuries. Musculoskeletal complications represent a large proportion of occupational health problems and, for this reason, have received increased attention from the sports industry. In this sense, studies on muscle fatigue should be intensified. Objective Verify muscle fatigue and injury involving the strain characteristics of lower limb joints in the eccentric and centripetal contraction of the jump. Methods A total of 691 individuals aged 20 to 40 years were selected. Fatigue was caused by active muscle contraction. The characteristic curves of active muscle contraction in different isometric, isotonic, and isokinetic training were analyzed. The degree of fatigue caused by three different sports states was tested by experimentation. The corresponding active muscle contraction characteristics were also analyzed. The potential for homeostasis at different ages was compared. Results The delay in recovery to fatigue is directly proportional to the athlete’s age. The return to post-exercise relief proportion from fatigue gradually decreases. Conclusion The experimental results showed that active muscle contraction could reduce exercise fatigue to some extent. This beneficial biochemical property of active muscle contraction is not found in people with advanced age. The findings have a guiding potential for the relief of sports fatigue. Evidence Level II; Therapeutic Studies - Investigating the result.

Forecasting football injuries by combining screening, monitoring and machine learning

Identifying players or circumstances associated with an increased risk of injury is fundamental for successful risk management in football. So far, time-constant and volatile risk factors are generally considered separately in either a screening (constant) or a monitoring (volatile) approach each resulting in a restricted set of explanatory variables. Consequently, improvements in predictive accuracy may be expected when screening and monitoring data are combined, especially when analysed with current machine learning (ML) techniques. This trial was designed as a prospective observational cohort study aiming to forecast non-contact time-loss injuries in male professional football (soccer). Injuries were registered according to the Fuller consensus. Gradient boosting with ROSE upsampling within a leave-one-out cross-validation was used for data analysis. The hierarchical data structure was considered throughout. Different splits of the original dataset were used to probe the robustness of results. Data of 88 players from 4 teams and 51 injuries could be analysed. The cross-validated performance of the gradient boosted model (ROC area under the curve 0.61) was promising and higher compared to models without integration of screening data. Importantly, holdout test set performance was similar (ROC area under the curve 0.62) indicating prospect of generalizability to new cases. However, the variation of predictive accuracy and feature importance with different splits of the original dataset reflects the relatively low number of events. It is concluded that ML-based injury forecasting based on the integration of screening and monitoring data is promising. However, external prospective verification and continued model development are required.

Integrative Proposals of Sports Monitoring: Subjective Outperforms Objective Monitoring

Current trends in sports monitoring are characterized by the massive collection of tech-based biomechanical, physiological and performance data, integrated through mathematical algorithms. However, the application of algorithms, predicated on mechanistic assumptions of how athletes operate, cannot capture, assess and adequately promote athletes' health and performance. The objective of this paper is to reorient the current integrative proposals of sports monitoring by re-conceptualizing athletes as complex adaptive systems (CAS). CAS contain higher-order perceptual units that provide continuous and multilevel integrated information about performer-environment interactions. Such integrative properties offer exceptional possibilities of subjective monitoring for outperforming any objective monitoring system. Future research should investigate how to enhance this human potential to contribute further to athletes' health and performance. This line of argument is not intended to advocate for the elimination of objective assessments, but to highlight the integrative possibilities of subjective monitoring.

Resilience in sports: a multidisciplinary, dynamic, and personalized perspective

Athletes are exposed to various psychological and physiological stressors, such as losing matches and high training loads. Understanding and improving the resilience of athletes is therefore crucial to prevent performance decrements and psychological or physical problems. In this review, resilience is conceptualized as a dynamic process of bouncing back to normal functioning following stressors. This process has been of wide interest in psychology, but also in the physiology and sports science literature (e.g. load and recovery). To improve our understanding of the process of resilience, we argue for a collaborative synthesis of knowledge from the domains of psychology, physiology, sports science, and data science. Accordingly, we propose a multidisciplinary, dynamic, and personalized research agenda on resilience. We explain how new technologies and data science applications are important future trends (1) to detect warning signals for resilience losses in (combinations of) psychological and physiological changes, and (2) to provide athletes and their coaches with personalized feedback about athletes' resilience.

Shoulder Tendon Adaptations Following a Graded Exercise Test to Exhaustion in Highly Trained Wheelchair Rugby Athletes With Different Impairments

Objective

This study aimed to identify acute changes in biceps and supraspinatus tendon characteristics before and after a graded exercise test to exhaustion (GXT) in highly trained wheelchair rugby (WR) athletes. A secondary aspect was to define chronic tendon adaptations related to the impairment of the athlete and the occupation of the tendon within the subacromial space (occupation ratio).

Methods

Twelve WR athletes with different impairments (age = 32 ± 6 years; body mass = 67.2 ± 11.2 kg; 9.0 ± 3.6 years competing) volunteered for this study. Performance Corrected Wheelchair Users Shoulder Pain Index was used to quantify shoulder pain. Quantitative Ultrasound Protocols (QUS) were used to define supraspinatus and biceps tendon thickness, echogenicity, and echogenicity ratio of both dominant and non-dominant shoulder before and after the GXT including 22 ± 3.1 min submaximal propulsion and 10.2 ± 1.7 min maximal propulsion on a treadmill. Furthermore, the acromio-humeral distance (AHD) defined from ultrasound (US) images was used to calculate the occupation ratios.

Results

A mixed-effect multilevel analysis that included shoulder as grouping variable, demonstrated a significant reduction in the echogenicity of the biceps following GXT whilst controlling for impairment [spinal cord injury (SCI) and non-SCI] and the occupation ratio (β = −9.01, SEβ = 2.72, p = 0.001, 95% CI = [−14.34; −3.68]). This points toward fluid inflow into the tendon that may be related to overload and acute inflammation. In addition, persons with a SCI (n = 8) had a thicker supraspinatus tendon in comparison to persons with non-SCI (n = 3) which may be related to chronic tendon adaptations (β = −0.53 mm, SEβ = 0.26, p = 0.038, 95% CI = [−1.04; −0.03]). Finally, a greater occupation ratio was associated with signs of tendinopathy (i.e., greater biceps and supraspinatus tendon thickness, and lower supraspinatus echogenicity and echogenicity ratio).

Conclusion

Acute biceps tendon adaptations in response to the GXT in highly trained WR athletes were evident with chronic adaptations in the supraspinatus tendon being related to the impairment of the athlete. Ultrasound can be used to monitor tendon adaptations in WR athletes for medical diagnosis to assist the scheduling and type of training.

Using Big Data-Based Neural Network Parallel Optimization Algorithm in Sports Fatigue Warning

In high-paced and efficient life and work, fatigue is one of the important factors that cause accidents such as traffic and medical accidents. This study designs a feature map-based pruning strategy (PFM), which effectively reduces redundant parameters and reduces the time and space complexity of parallelized deep convolutional neural network (DCNN) training; a correction is proposed in the Map stage. The secant conjugate gradient method (CGMSE) realizes the fast convergence of the conjugate gradient method and improves the convergence speed of the network; in the Reduce stage, a load balancing strategy to control the load rate (LBRLA) is proposed to achieve fast and uniform data grouping to ensure the parallelization performance of the parallel system. Finally, the related fatigue algorithm's research and simulation based on the human eye are carried out on the PC. The human face and eye area are detected from the video image collected using the USB camera, and the frame difference method and the position information of the human eye on the face are used. To track the human eye area, extract the relevant human eye fatigue characteristics, combine the blink frequency, closed eye duration, PERCLOS, and other human eye fatigue determination mechanisms to determine the fatigue state, and test and verify the designed platform and algorithm through experiments. This system is designed to enable people who doze off, such as drivers, to discover their state in time through the system and reduce the possibility of accidents due to fatigue.

Fatigue Induced by Repeated Changes of Direction in Élite Female Football (Soccer) Players: Impact on Lower Limb Biomechanics and Implications for ACL Injury Prevention

Background

The etiology of Anterior Cruciate Ligament (ACL) injury in women football results from the interaction of several extrinsic and intrinsic risk factors. Extrinsic factors change dynamically, also due to fatigue. However, existing biomechanical findings concerning the impact of fatigue on the risk of ACL injuries remains inconsistent. We hypothesized that fatigue induced by acute workload in short and intense game periods, might in either of two ways: by pushing lower limbs mechanics toward a pattern close to injury mechanism, or alternatively by inducing opposed protective compensatory adjustments.

Aim

In this study, we aimed at assessing the extent to which fatigue impact on joints kinematics and kinetics while performing repeated changes of direction (CoDs) in the light of the ACL risk factors.

Methods

This was an observational, cross-sectional associative study. Twenty female players (age: 20-31 years, 1st-2nd Italian division) performed a continuous shuttle run test (5-m) involving repeated 180°-CoDs until exhaustion. During the whole test, 3D kinematics and ground reaction forces were used to compute lower limb joints angles and internal moments. Measures of exercise internal load were: peak post-exercise blood lactate concentration, heart rate (HR) and perceived exertion. Continuous linear correlations between kinematics/kinetics waveforms (during the ground contact phase of the pivoting limb) and the number of consecutive CoD were computed during the exercise using a Statistical Parametric Mapping (SPM) approach.

Results

The test lasted 153 ± 72 s, with a rate of 14 ± 2 CoDs/min. Participants reached 95% of maximum HR and a peak lactate concentration of 11.2 ± 2.8 mmol/L. Exercise duration was inversely related to lactate concentration (r = -0.517, p < 0.01), while neither%HR _max nor [La^-] _b nor RPE were correlated with test duration before exhaustion (p > 0.05). Alterations in lower limb kinematics were found in 100%, and in lower limb kinetics in 85% of the players. The most common kinematic pattern was a concurrent progressive reduction in hip and knee flexion angle at initial contact (10 players); 5 of them also showed a significantly more adducted hip. Knee extension moment decreased in 8, knee valgus moment increased in 5 players. A subset of participants showed a drift of pivoting limb kinematics that matches the known ACL injury mechanism; other players displayed less definite or even opposed behaviors.

Discussion

Players exhibited different strategies to cope with repeated CoDs, ranging from protective to potentially dangerous behaviors. While the latter was not a univocal effect, it reinforces the importance of individual biomechanical assessment when coping with fatigue.

Systematic Video Analysis of Anterior Cruciate Ligament Injuries in Professional Female Soccer Players

BACKGROUND

Female soccer players are particularly susceptible to anterior cruciate ligament (ACL) injuries, accounting for 16% to 43% of the injury burden during the season. Despite the advancements in injury prevention programs, the rate of ACL injuries continues to rise.

PURPOSE

To provide a comprehensive description of the mechanisms, situational pattern, and biomechanics of ACL injuries in women's soccer.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

We identified 57 consecutive ACL injuries that occurred in matches of 6 top female leagues across 3 seasons (2017-2020). A total of 35 (61%) injury videos were analyzed for the mechanism and situational pattern, while biomechanical analysis was possible in 29 cases. Three independent reviewers evaluated each video. The distribution of ACL injuries according to month, timing within the match, and field location at the time of injury was also reported.

RESULTS

In the 35 injury videos, there were 19 (54%) noncontact injuries, 12 (34%) indirect contact injuries, and 4 (11%) direct contact injuries. We identified 3 main situations in players who suffered a noncontact/indirect contact injury: (1) pressing and tackling (n = 18), (2) regaining balance after kicking (n = 7), and (3) being tackled (n = 4). Biomechanical analysis indicated multiplanar mechanisms with frequent knee valgus loading (88%). Additionally, 64% of injuries occurred in the first half of matches and most frequently within the first 30 minutes.

CONCLUSION

Female athletes showed remarkable similarities with elite male players in terms of the ACL mechanism and situational pattern of injury, and 88% of injuries involved no direct contact to the knee, with noncontact injuries being highly prevalent. Injuries occurred during 3 main situations, with accompanying alterations in multiplanar biomechanics. Interventions aimed at reducing ACL injuries in women's soccer should consider high-intensity defensive play at the beginning of a match. Instruction in the 3 main situations should be applied alongside appropriate neuromuscular training interventions.

Healthy Teleworking: Towards Personalized Exercise Recommendations

Home-based teleworking, associated with sedentary behavior, may impair self-reported adult health status. Current exercise recommendations, based on universal recipes, may be insufficient or even misleading to promote healthy teleworking. From the Network Physiology of Exercise perspective, health is redefined as an adaptive emergent state, product of dynamic interactions among multiple levels (from genetic to social) that cannot be reduced to a few dimensions. Under such a perspective, fitness development is focused on enhancing the individual functional diversity potential, which is better achieved through varied and personalized exercise proposals. This paper discusses some myths related to ideal or unique recommendations, like the ideal exercise or posture, and the contribution of recent computer technologies and applications for prescribing exercise and assessing fitness. Highlighting the need for creating personalized working environments and strengthening the active contribution of users in the process, new recommendations related to teleworking posture, home exercise counselling, exercise monitoring and to the roles of healthcare and exercise professionals are proposed. Instead of exercise prescribers, professionals act as co-designers that help users to learn, co-adapt and adequately contextualize exercise in order to promote their somatic awareness, job satisfaction, productivity, work–life balance, wellbeing and health.

Sports Injury Forecasting and Complexity: A Synergetic Approach

The understanding that sports injury is the result of the interaction among many factors and that specific profiles could increase the risk of the occurrence of a given injury was a significant step in establishing programs for injury prevention. However, injury forecasting is far from being attained. To be able to estimate future states of a complex system (forecasting), it is necessary to understand its nature and comply with the methods usually used to analyze such a system. In this sense, sports injury forecasting must implement the concepts and tools used to study the behavior of self-organizing systems, since it is by self-organizing that systems (i.e., athletes) evolve and adapt (or not) to a constantly changing environment. Instead of concentrating on the identification of factors related to the injury occurrence (i.e., risk factors), a complex systems approach looks for the high-order variables (order parameters) that describe the macroscopic dynamic behavior of the athlete. The time evolution of this order parameter informs on the state of the athlete and may warn about upcoming events, such as injury. In this article, we describe the fundamental concepts related to complexity based on physical principles of self-organization and the consequence of accepting sports injury as a complex phenomenon. In the end, we will present the four steps necessary to formulate a synergetics approach based on self-organization and phase transition to sports injuries. Future studies based on this experimental paradigm may help sports professionals to forecast sports injuries occurrence.

Interlimb Coordination: A New Order Parameter and a Marker of Fatigue During Quasi-Isometric Exercise?

Although exercise-induced fatigue has been mostly studied from a reductionist and component-dominant approach, some authors have started to test the general predictions of theories of self-organized change during exercises performed until exhaustion. However, little is known about the effects of fatigue on interlimb coordination in quasi-isometric actions. The aim of this study was to investigate the effect of exercise-induced fatigue on upper interlimb coordination during a quasi-isometric exercise performed until exhaustion. In order to do this, we hypothesized an order parameter that governs the interlimb coordination as an interlimb correlation measure. In line with general predictions of theory of phase transitions, we expected that the locally averaged values of the order parameter will increase as the fatigue driven system approaches the point of spontaneous task disengagement. Seven participants performed a quasi-isometric task holding an Olympic bar maintaining an initial elbow flexion of 90 degrees until fatigue induced spontaneous task disengagement. The variability of the elbow angle was recorded through electrogoniometry and the obtained time series were divided into three segments for further analysis. Running correlation function (RCF) and adopted bivariate phase rectified signal averaging (BPRSA) were applied to the corresponding initial (30%) and last (30%) segments of the time series. The results of both analyses showed that the interlimb correlation increased between the initial and the final segments of the performed task. Hence, the hypothesis of the research was supported by evidence. The enhancement of the correlation in the last part means a less flexible coordination among limbs. Our results also show that the high magnitude correlation (%RCF > 0.8) and the %Range (END-BEG) may prove to be useful markers to detect the effects of effort accumulation on interlimb coordination. These results may provide information about the loss of adaptability during exercises performed until exhaustion. Finally, we briefly discuss the hypothesis of the inhibitory percolation process being the general explanation of the spontaneous task disengagement phenomenon.

Self-Reported Physical Activity, Injury, and Illness in Canadian Adolescent Ski Racers

Youth ski racers spend a considerable amount of time on snow and this may detract from other activities known to influence fundamental movement skills and overall health related outcomes. Parents of racers (n = 52 F; n = 44 M; age range 9–14 years) registered in the Canadian club system completed a baseline medical questionnaire during preseason testing in 2017. We describe physical activity volume and sport participation outside of physical education classes over the previous 12 months and report on injuries, medication use and health care utilization. The mean number of activities participated was five (range 1–14) with cycling, hiking, and swimming as the preferred choice and a cumulative mean of just under 400 h of activity was reported (range F 27–1,015; M 62–869 h/year) in the past year. During the past 12 months 16% of the athletes reported being injured and injury severity impacted return to sport with range of reported days missed from 1 to 365 days. Thirteen non-concussive injuries were reported in alpine skiing and females (12%, 6/52) reported more lower limb injuries than males (7%, 3/44). More males were concussed over their lifetime, with alpine skiing accounting for 46% and mountain biking 15%. Most athletes (85%) did not take medication on a regular basis and those that did had a medical diagnosis. The frequency of respiratory conditions was 13% (12/96) with males reporting slightly more cases than females. No difference in emergency visits occurred (25%) between males and females in the past 12 months, however females reported more (n = 102) allied health care, sport medicine and x-rays appointments when compared to males (n = 65). In summary, a high volume of physical activity (an hour plus per day) over the previous 12 months was reported with racers participating in several activities outside of skiing, likely honing their fundamental movement skills. Close proximity to the mountains may have influenced their choices of activity outside of ski racing, and their injuries and a variety of health conditions were typical of their age group. Future research employing wearable technology to objectively quantify the volume and intensity of physical activity participation is recommended.

Network Physiology of Exercise: Vision and Perspectives

The basic theoretical assumptions of Exercise Physiology and its research directions, strongly influenced by reductionism, may hamper the full potential of basic science investigations, and various practical applications to sports performance and exercise as medicine. The aim of this perspective and programmatic article is to: (i) revise the current paradigm of Exercise Physiology and related research on the basis of principles and empirical findings in the new emerging field of Network Physiology and Complex Systems Science; (ii) initiate a new area in Exercise and Sport Science, Network Physiology of Exercise (NPE), with focus on basic laws of interactions and principles of coordination and integration among diverse physiological systems across spatio-temporal scales (from the sub-cellular level to the entire organism), to understand how physiological states and functions emerge, and to improve the efficacy of exercise in health and sport performance; and (iii) to create a forum for developing new research methodologies applicable to the new NPE field, to infer and quantify nonlinear dynamic forms of coupling among diverse systems and establish basic principles of coordination and network organization of physiological systems. Here, we present a programmatic approach for future research directions and potential practical applications. By focusing on research efforts to improve the knowledge about nested dynamics of vertical network interactions, and particularly, the horizontal integration of key organ systems during exercise, NPE may enrich Basic Physiology and diverse fields like Exercise and Sports Physiology, Sports Medicine, Sports Rehabilitation, Sport Science or Training Science and improve the understanding of diverse exercise-related phenomena such as sports performance, fatigue, overtraining, or sport injuries.

Dynamic Knee Valgus in Single-Leg Movement Tasks. Potentially Modifiable Factors and Exercise Training Options. A Literature Review

Dynamic knee valgus (DKV) as an incorrect movement pattern is recognized as a risk factor for lower limb injuries. Therefore, it is important to find the reasons behind this movement to select effective preventive procedures. There is a limited number of publications focusing on specific tasks, separating the double-leg from the single-leg tasks. Test patterns commonly used for DKV assessment, such as single-leg squat (SLS) or single leg landings (SLL), may show different results. The current review presents the modifiable factors of knee valgus in squat and landing single-leg tests in healthy people, as well as exercise training options. The authors used the available literature from PubMed, Scopus, PEDro and clinicaltrials.gov databases, and reviewed physiotherapy journals and books. For the purpose of the review, studies were searched for using 2D or 3D motion analysis methods only in the SLL and SLS tasks among healthy active people. Strengthening and activating gluteal muscles, improving trunk lateral flexion strength, increasing ROM dorsiflexion ankle and midfoot mobility should be taken into account when planning training programs aimed at reducing DKV occurring in SLS. In addition, knee valgus during SLL may occur due to decreased hip abductors, extensors, external rotators strength and higher midfoot mobility. Evidence from several studies supports the addition of biofeedback training exercises to reduce the angles of DKV.

Higher Vertical Jumping Asymmetries and Lower Physical Performance are Indicators of Increased Injury Incidence in Youth Team-Sport Athletes

Fort-Vanmeerhaeghe, A, Milà-Villarroel, R, Pujol-Marzo, M, Arboix-Alió, J, and Bishop, C. Higher vertical jumping asymmetries and lower physical performance are indicators of increased injury incidence in youth team-sport athletes. J Strength Cond Res XX(X): 000-000, 2020-To date, the literature about the association between injury-risk factors and actual injury incidence in young elite team-sports athletes is scarce. The main objective of this study was to examine how modifiable factors may affect injury incidence. Eighty-one young elite team-sports athletes (age: under-14 to under-18) performed the countermovement jump (CMJ), a single leg CMJ (SLCMJ), the one-legged hop test (OLHT), a 30-m sprint test, the V-cut test, a repeated sprint ability, and the 30-15 intermittent fitness test (IFT) during the pre-season period. Interlimb asymmetries were calculated for SLCMJ and OLHT. Injuries were recorded prospectively for the entirety of the 2017-2018 season. Comparison of injury and noninjury data was performed using a two-way analysis of variance (ANOVA). Results of the ANOVA according to injury showed significant differences in CMJ (p = 0.01), SLCMJ on the lowest performing limb (p = 0.03), and SLCMJ asymmetry (<0.001). Sex × injury interaction was significant from CMJ (p = 0.018) and 30-15 IFT (p = <0.001). In conclusion, this study indicated that athletes with greater interlimb asymmetries, less vertical jump capacity, and lower intermittent aerobic fitness had a greater predisposition to injury. Therefore, monitoring CMJ, aerobic performance, and interlimb asymmetries is recommended given their sensitivity to detect significant differences between injured and healthy youth athletes.

Effects of an 8-week basketball-specific proprioceptive training with a single-plane instability balance platform

BACKGROUND

To avoid injuries in basketball players, they are recommended to pay more attention to improve their body balance. Therefore new training methods and equipment need to be devised. This study examined the effects of an 8-week basketball-specific proprioception training program while using a new developed one plane instability balance board during warm-up for improving balance ability in basketball players. Players who obtained basketball-specific balance training were compared to a control group.

METHODS

Thirty-one male university basketball players (age: 21.35, SD = 0.605 years; height: 190.97, SD = 1.88; body mass: 86.95, SD = 2.61) participated in this study. Seventeen participants were assigned to the basketball-specific 8-week balance training group (BTG) while 14 participants served as a control group (CG). Both groups were tested with the Y balance test (YBT) and postural stability test (PST) at baseline and 8 weeks later.

RESULTS

The results indicate significant improvements in the overall YBT for both legs in BTG, but not in CG. However, no group differences were found for dynamic balance performance, but static balance (i.e., postural stability) differed between groups after 8 weeks. A statistically significant moderate inverse correlation was computed between the total score of YBT and the total score of the overall stability index (r=-0.404; p= 0.041).

CONCLUSIONS

An 8-week basketball-specific proprioception training program with a single-plane instability balance platform improved balance ability (Y balance test and postural stability test) of basketball players.

Training or Synergizing? Complex Systems Principles Change the Understanding of Sport Processes

There is a need to update scientific assumptions in sport to promote the critical thinking of scientists, coaches, and practitioners and improve their methodological decisions. On the basis of complex systems science and theories of biological evolution, a systematization and update of theoretical and methodological principles to transform the understanding of sports training is provided. The classical focus on learning/acquiring skills and fitness is replaced by the aim of increasing the diversity/unpredictability potential of teams/athletes through the development of synergies. This development is underpinned by the properties of hierarchical organization and circular causality of constraints, that is, the nestedness of constraints acting at different levels and timescales. These properties, that integrate bottom-up and top-down all dimensions and levels of performance (from social to genetic), apply to all types of sport, ages, or levels of expertise and can be transferred to other fields (e.g., education, health, management). The team as the main training unit of intervention, the dynamic concept of task representativeness, and the co-adaptive and synergic role of the agents are some few practical consequences of moving from training to synergizing.

Statement on methods in sport injury research from the 1st METHODS MATTER Meeting, Copenhagen, 2019

High quality sports injury research can facilitate sports injury prevention and treatment. There is scope to improve how our field applies best practice methods—methods matter (greatly!). The 1st METHODS MATTER Meeting, held in January 2019 in Copenhagen, Denmark, was the forum for an international group of researchers with expertise in research methods to discuss sports injury methods. We discussed important epidemiological and statistical topics within the field of sports injury research. With this opinion document, we provide the main take-home messages that emerged from the meeting.

Statement on Methods in Sport Injury Research From the First METHODS MATTER Meeting, Copenhagen, 2019

High-quality sports injury research can facilitate sports injury prevention and treatment. There is scope to improve how our field applies best-practice methods-methods matter (greatly!). The first METHODS MATTER meeting, held in January 2019 in Copenhagen, Denmark, was the forum for an international group of researchers with expertise in research methods to discuss sports injury methods. We discussed important epidemiological and statistical topics within the field of sports injury research. With this opinion document, we provide the main take-home messages that emerged from the meeting. Meeting participants agreed that the definition of sport injury depends on the research question and context. It was considered essential to be explicit about the goal of the research effort and to use frameworks to illustrate the assumptions that underpin measurement and the analytical strategy. Complex systems were discussed to illustrate how potential risk factors can interact in a nonlinear way. This approach is often a useful alternative to identifying single risk factors. Investigating changes in exposure status over time is important when analyzing sport injury etiology, and analyzing recurrent injury, subsequent injury, or injury exacerbation remains challenging. The choice of statistical model should consider the research question, injury measure (eg, prevalence, incidence), type and granularity of injury data (categorical or continuous), and study design. Multidisciplinary collaboration will be a cornerstone for future high-quality sport injury research. Working outside professional silos in a diverse, multidisciplinary team benefits the research process, from the formulation of research questions and designs to the statistical analyses and dissemination of study results in implementation contexts. This article has been copublished in the British Journal of Sports Medicine and the Journal of Orthopaedic & Sports Physical Therapy. J Orthop Sports Phys Ther 2020;50(5):226-233. doi:10.2519/jospt.2020.9876.

Criteria-Based Return to Sport Decision-Making Following Lateral Ankle Sprain Injury: a Systematic Review and Narrative Synthesis

OBJECTIVE

The aim of this systematic review was to identify prospective studies that used a criteria-based return to sport (RTS) decision-making process for patients with lateral ankle sprain (LAS) injury.

DESIGN

Systematic review and narrative synthesis.

DATA SOURCES

The PubMed (MEDLINE), Web of Science, PEDro, Cochrane Library, SPORTDiscus (EBSCO), ScienceDirect, and Scopus databases were searched to 23 November 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies were included if they prospectively applied a criteria-based RTS decision-making process for patients with LAS injury, but were excluded if they merely gathered outcome measures at the RTS time point. Studies were also excluded if patients were recovering from ankle fracture, high ankle sprain, medial ankle sprain, chronic ankle instability or complex ankle injury.

RESULTS

No studies were identified that used a criteria-based RTS decision-making process for patients with LAS injury. We were unable to conduct a quantitative synthesis or meta-analysis, therefore we provide a narrative synthesis of relevant questionnaires, as well as clinical and functional assessments commonly used in studies retrieved in the search.

CONCLUSION

There are currently no published evidence-based criteria to inform RTS decisions for patients with an LAS injury. Based on our narrative synthesis, we propose a number of variables that could be used to develop a criteria-based RTS decision paradigm. Future research should aim to reach consensus on these variables and apply them to actual RTS decisions within prospective study designs. Furthermore, we suggest that complex systems theory and the RTS continuum could be used to inform the development of an RTS decision-making paradigm for athletes with LAS injury.

The practical application of a method of analysing the variability of within-step accelerations collected via athlete tracking devices

Resolving intra-stride accelerations from training and game data routinely collected by athlete tracking devices is rarely attempted, even though these data can provide important insights into the physical condition of athletes. This study describes in detail a novel analysis tool which uses accelerometer-based measures of step variability to assess longitudinal consistency of stride technique. The performance of the analysis tool was examined by combining results from the analysis of data collected over the course of an Australian Football League season with instances of missed or modified training. Results demonstrated increased gait-related trunk acceleration variability when training was modified due to load or accumulated game and training activity (p = 0.02) and reduced trunk acceleration variability in the week following a training modification due to any injury described as "ankle", "heel", or any other description that would loosely refer to a joint or bone in the leg (p = 0.01). These results support the findings of recent research which used a slightly modified version of the same analysis tool to demonstrate an increase in gait-related trunk acceleration variability with the increased acute physical load.

Revised Approach to the Role of Fatigue in Anterior Cruciate Ligament Injury Prevention: A Systematic Review with Meta-Analyses

BACKGROUND

Causes of anterior cruciate ligament (ACL) injuries are multifactorial. Anterior cruciate ligament injury prevention should thus be approached from a multifactorial perspective as well. Training to resist fatigue is an underestimated aspect of prevention programs given that the presence of fatigue may play a crucial role in sustaining an ACL injury.

OBJECTIVES

The primary objective of this literature review was to summarize research findings relating to the kinematic and kinetic effects of fatigue on single-leg landing tasks through a systematic review and meta-analysis. Other objectives were to critically appraise current approaches to examine the effects of fatigue together with elucidating and proposing an optimized approach for measuring the role of fatigue in ACL injury prevention.

METHODS

A systematic literature search was conducted in the databases PubMed (1978-November 2017), CINAHL (1992-November 2017), and EMBASE (1973-November 2017). The inclusion criteria were: (1) full text, (2) published in English, German, or Dutch, (3) healthy subjects, (4) average age ≥ 18 years, (5) single-leg jump landing task, (6) evaluation of the kinematics and/or kinetics of the lower extremities before and after a fatigue protocol, and (7) presentation of numerical kinematic and/or kinetic data. Participants included healthy subjects who underwent a fatigue protocol and in whom the effects of pre- and post-fatigue on three-dimensional lower extremity kinematic and kinetics were compared. Methods of data collection, patient selection, blinding, prevention of verification bias, and study design were independently assessed.

RESULTS

Twenty studies were included, in which four types of single-leg tasks were examined: the single-leg drop vertical jump, the single-leg drop landing, the single-leg hop for distance, and sidestep cutting. Fatigue seemed to mostly affect initial contact (decreased angles post-fatigue) and peak (increased angles post-fatigue) hip and knee flexion. Sagittal plane variables at initial contact were mostly affected under the single-leg hop for distance and sidestep cutting conditions whilst peak angles were affected during the single-leg drop jump.

CONCLUSIONS

Training to resist fatigue is an underestimated aspect of prevention programs given that the presence of fatigue may play a crucial role in sustaining an ACL injury. Considering the small number of variables affected after fatigue, the question arises whether the same fatigue pathways are affected by the fatigue protocols used in the included laboratory studies as are experienced on the sports field.

Perceived Fatigability: Utility of a Three-Dimensional Dynamical Systems Framework to Better Understand the Psychophysiological Regulation of Goal-Directed Exercise Behaviour

A three-dimensional framework of perceived fatigability emphasises the need to differentiate between the qualitatively distinct inputs of sensory-discriminatory, affective-motivational and cognitive-evaluative processes that shape the perceptual milieu during prolonged endurance exercise. This article reviews the framework's utility to better understand how cause-effect relationships come to be and how perception-action coupling underpins pacing behaviour and performance fatigability. Preliminary evidence supports the hypotheses that perceived strain plays a primary role in trajectory regulation of pacing behaviour, core affect plays a primary and mediatory role in behavioural performance regulation, and the mindset shift associated with an action crisis plays a primary role in the intensity dependent volitional self-regulatory control of conflicting motivational drives. The constructs hypothesised to underpin perceived fatigability are systematically linked, context-dependent, constraint-based, distinguishable and show proportional continuous interdependency. They are further interrelated with dynamic changes in pacing behaviour, performance fatigability and physiological disturbance. Appropriate measurement selections for the subordinate constructs perceived physical strain, perceived mental strain, valence, arousal, action crisis and flow state are discussed. To better understand the non-proportional discontinuous effects of fatigue on discrete shifts in thought states and mindsets, non-linear dynamical systems theory is introduced as an unbiased overarching theory of governing principles in the temporal evolution of complex systems. This provides the opportunity to discuss the bio-psycho-social fatigue phenomenon from a dynamical and holistic perspective. The proposed framework offers a sophisticated alternative to the Gestalt concept of perceived exertion and comprehensively accounts for the psychophysiological processes that determine pacing behaviour and performance. It has the potential to enrich theory development and facilitate a deeper understanding of the psychophysiological regulation of goal-directed exercise behaviour.

Assessing the Return on Investment of Injury Prevention Procedures in Professional Football

INTRODUCTION

The aim of this study was to develop a quick and simple screening procedure for evaluating the return on investment provided by injury prevention programmes in professional football. Injury prevention in sport has usually been considered in isolation of other management responsibilities, and interventions are published irrespective of whether their impact is worthwhile and irrespective of the return on players' time investment in the programme. This approach is naive from a business perspective and is not an approach normally adopted by commercial organisations.

METHODS

In professional football, the overwhelming cost associated with implementing an injury prevention programme is the players' time commitment, and the major benefit is the players' increased availability, achieved through the reduction in the number of injuries. A comparison of these time-based costs and benefits provides the basis for the evaluation process presented.

RESULTS

Applying the evaluation process to a number of published injury prevention programmes recommended for football demonstrates that they are unlikely to provide an adequate return on investment.

CONCLUSIONS

Researchers should focus on developing injury prevention programmes that provide an adequate return on players' time investment, otherwise there is no incentive for clubs to implement the programmes. Reporting that an injury prevention programme produces a statistically significant reduction in the incidence of injury, for example, is insufficient information. Injury prevention programmes should focus on 'at risk' players to increase the return on investment, and researchers should evaluate and report on the utility of prevention programmes within the intended sports setting.

On the Relatedness and Nestedness of Constraints

The purpose of this opinion paper is providing a platform for explaining and discussing the relatedness and nestedness of constraints on the basis of four claims: (a) task constraints are distributed between the person and the environment and hence are relational variables, (b) being relational, task constraints are also emergent properties of the organism/environment system, (c) constraints are nested in timescales, and (d) a vast set of constraints are correlated through circular causality. Theoretical implications for improving the understanding of the constraints-led approach and practical applications for enhancing the manipulation of constraints in learning and training settings are proposed.