Unlocking the potential of big data to support tactical performance analysis in professional soccer: A systematic review.

In professional soccer, increasing amounts of data are collected that harness great potential when it comes to analysing tactical behaviour. Unlocking this potential is difficult as big data challenges the data management and analytics methods commonly employed in sports. By joining forces with computer science, solutions to these challenges could be achieved, helping sports science to find new insights, as is happening in other scientific domains. We aim to bring multiple domains together in the context of analysing tactical behaviour in soccer using position tracking data. A systematic literature search for studies employing position tracking data to study tactical behaviour in soccer was conducted in seven electronic databases, resulting in 2338 identified studies and finally the inclusion of 73 papers. Each domain clearly contributes to the analysis of tactical behaviour, albeit in - sometimes radically - different ways. Accordingly, we present a multidisciplinary framework where each domain's contributions to feature construction, modelling and interpretation can be situated. We discuss a set of key challenges concerning the data analytics process, specifically feature construction, spatial and temporal aggregation. Moreover, we discuss how these challenges could be resolved through multidisciplinary collaboration, which is pivotal in unlocking the potential of position tracking data in sports analytics.

A critical analysis of limb symmetry indices of hop tests in athletes after anterior cruciate ligament reconstruction: A case control study.

BACKGROUND: Hop tests are frequently used to determine return to sports (RTS) after anterior cruciate ligament reconstruction (ACLR). Given that bilateral deficits are present after ACLR, this may result in a falsely high limb symmetry index (LSI), since LSI is calculated as a ratio between the values of the limbs. HYPOTHESIS: Athletes after ACLR would achieve LSI>90% for the hop test. Secondly, athletes after ACLR demonstrate decreased jump distance on the single hop for distance (SLH) and triple leg hop for distance (TLH) and decreased number of hops for the side hop (SH) for both involved and uninvolved limbs compared to normative data of sex, age and type of sports matched healthy athletes. MATERIALS AND METHODS: Fifty-two patients (38 males mean age 23.9±3.5years; 14 females mean age 21.7±3.5 years) who had undergone an ACLR participated in this study. Patients performed the 3 hop tests at a mean time of 7 months after ACLR. Hop distance, number of side hops and LSI were compared with normative data of 188 healthy athletes. RESULTS: The differences between the involved limb and the uninvolved limb were significant in all hop tests (SLH P=0.003, TLH P=0.003, SH P=0.018). For females, only significant between limb differences were found in the SLH (P=0.049). For both the SLH and the TLH, significant differences were found between the involved limb and the normative data (males; SLH P<0.001, TLH P<0.001; females; SLH P<0.001, TLH P=0.006) and between the uninvolved limb and the normative data for both males and females (males; SLH P<0.001, TLH P<0.001; females; SLH P=0.003, TLH P=0.038). For the SH, only significant differences were found between the involved limb and the normative values in males (P=0.033). CONCLUSION: Athletes who have undergone an ACLR demonstrate bilateral deficits on hop tests in comparison to age and sex matched normative data of healthy controls. Using the LSI may underestimate performance deficits and should therefore be analyzed with caution when used as a criterion for RTS after ACLR. LEVEL OF EVIDENCE: III, case control study.

Rocking the boat: does perfect rowing crew synchronization reduce detrimental boat movements?

In crew rowing, crew members need to mutually synchronize their movements to achieve optimal crew performance. Intuitively, poor crew coordination is often deemed to involve additional boat movements such as surge velocity fluctuations, heave, pitch, and roll, which would imply lower efficiency (eg, due to increased hydrodynamic drag). The aim of this study was to investigate this alleged relation between crew coordination and boat movements at different stroke rates. Fifteen crews of two rowers rowed in a double scull (ie, a two-person boat) at 18, 22, 26, 30, and 34 strokes per minute. Oar angles (using potentiometers) and movements of the boat (using a three-axial accelerometer-gyroscope sensor) were measured (200 Hz). Results indicated that crew synchronization became more consistent with stroke rate, while surge, heave, and pitch fluctuations increased. Further, within each stroke rate condition, better crew synchronization was related to less roll of the boat, but increased fluctuations regarding surge, heave, and pitch. Together this demonstrates that while better crew synchronization relates to enhanced lateral stability of the boat, it inevitably involves more detrimental boat movements and hence involves lower biomechanical efficiency.

Jump Landing Characteristics Predict Lower Extremity Injuries in Indoor Team Sports.

The aim of this study is to investigate the predictive value of landing stability and technique to gain insight into risk factors for ankle and knee injuries in indoor team sport players. Seventy-five male and female basketball, volleyball or korfball players were screened by measuring landing stability after a single-leg jump landing and landing technique during a repeated counter movement jump by detailed 3-dimensional kinematics and kinetics. During the season 11 acute ankle injuries were reported along with 6 acute and 7 overuse knee injuries by the teams' physical therapist. Logistic regression analysis showed less landing stability in the forward and diagonal jump direction (OR 1.01-1.10, p≤0.05) in players who sustained an acute ankle injury. Furthermore landing technique with a greater ankle dorsiflexion moment increased the risk for acute ankle injury (OR 2.16, p≤0.05). A smaller knee flexion moment and greater vertical ground reaction force increased the risk of an overuse knee injury (OR 0.29 and 1.13 respectively, p≤0.05). Less one-legged landing stability and suboptimal landing technique were shown in players sustaining an acute ankle and overuse knee injury compared to healthy players. Determining both landing stability and technique may further guide injury prevention programs.

Monitoring Perceived Stress and Recovery in Relation to Cycling Performance in Female Athletes.

The purpose was to investigate perceived stress and recovery related to cycling performance of female athletes over one full year. 20 female athletes (age, 27±8 years; ˙VO2max, 50.3±4.6 mL·kg(-1)·min(-1)) were measured 8 times in one year to determine perceived stress and recovery (RESTQ-Sport) in relation to cycling performance (Lamberts and Lambert Submaximal Cycle Test (LSCT)). All 19 RESTQ-Sport scales were calculated and scores of the 4 main categories were determined (i. e., general stress, general recovery, sport-specific stress and sport-specific recovery). A balance score of total stress and recovery was calculated by recovery-stress. Power at the second stage (P80), third stage (P90) and heart rate recovery (HRR60 s) of the LSCT were determined as performance parameters. 110 RESTQ-Sports and LSCTs were analysed using a multilevel approach (random intercepts model). Higher self-efficacy was related to improvement of all performance parameters. Higher total recovery stress, and lower emotional stress were related to improvement of P90 and HRR60 s. Higher sport-specific recovery was related to P80, higher general stress, fatigue and physical complaints were related to decreased P90 and higher social stress and injury were related to decreased HRR60 s. Improved perceived recovery and stress contributed to an improved performance. Relevant information could be provided by monitoring changes in perceived stress and recovery of female athletes.

A Negative Life Event Impairs Psychosocial Stress, Recovery and Running Economy of Runners.

The purpose was to investigate how a negative life event (NLE) affects perceived psychosocial stress, recovery and running economy (RE). Competitive runners were monitored in a prospective non-experimental cohort study over one full training season in which they experienced the same unplanned severe NLE. 16 runners recorded stress and recovery scores (RESTQ-Sport) every week. The average scores over 3 weeks before the NLE were used as a baseline and were compared to scores during the week of the NLE (week 0), week 1 and week 2. 7 runners completed a submaximal treadmill test before and after the NLE. Repeated measures ANOVAs revealed that most scores on general stress scales were increased in week 0 and 1. Of the general recovery scales, "general well-being" was decreased in week 0 and 1, "social" and "physical recovery" were decreased in week 0. No changes in the sport-specific stress scales were found. However, 2 of the sport-specific recovery scales were decreased in week 0. An impaired RE was shown 3 weeks after the NLE. Therefore, it is important to know what is going on in an athlete's life, because stressful life events alter RE after the stress and recovery already returned to normal levels.

The Effect of Stress and Recovery on Field-test Performance in Floorball.

Physical and psychosocial stress and recovery are important performance determinants. A holistic approach that monitors these performance determinants over a longer period of time is lacking. Therefore this study aims to investigate the effect of a player's physical and psychosocial stress and recovery on field-test performance. In a prospective non-experimental cohort design 10 female Dutch floorball players were monitored over 6 months. To monitor physical and psychosocial stress and recovery, daily training-logs and 3-weekly the Recovery-Stress Questionnaire for Athletes (RESTQ-Sport) were filled out respectively. To determine field-test performance 6 Heart rate Interval Monitoring System (HIMS) and 4 Repeated Modified Agility T-test (RMAT) measurements were performed. Multilevel prediction models were applied to account for within-players and between-players field-test performance changes. The results show that more psychosocial stress and less psychosocial recovery over 3-6 weeks before testing decrease HIMS performance (p≤0.05). More physical stress over 6 weeks before testing improves RMAT performance (p≤0.05). In conclusion, physical and psychosocial stress and recovery affect submaximal interval-based running performance and agility up to 6 weeks before testing. Therefore both physical and psychosocial stress and recovery should be monitored in daily routines to optimize performance.

Changes in perceived stress and recovery in overreached young elite soccer players.

The aim of this study was to prospectively monitor sport-specific performance and assess the stress-recovery balance in overreached (OR) soccer players and controls. During two competitive seasons, 94 players participated in the study. The stress-recovery balance (RESTQ-Sport) and sport-specific performance (Interval Shuttle Run Test) were assessed monthly. Seven players with performance decrement of at least a month were classified as OR. Stress and recovery measures were assessed between groups (OR vs healthy players) and at different times within the OR group. An unfavorable total recovery score appeared 2 months before diagnosis when compared with the reference values of the healthy group established at the start of the season (P=0.009) and also over the two seasons (P=0.028). The scales Emotional Stress (P=0.044), Physical Recovery (P=0.009), General Well-being (P=0.001) and Sleep Quality (P=0.045) were sensitive to OR compared with the average of the healthy group over the two seasons. Finally, Fatigue and Being in Shape demonstrated the largest changes in stress and recovery within the OR players (effect size=1.14 and 1.50). The longitudinal monitoring of performance and changes in stress and recovery may be useful for the detection of OR in its earliest stage. The information obtained from these tests can be used to optimize individual training and recovery programs.

A job-related fitness test for the Dutch police.

BACKGROUND: The variety of tasks that characterize police work highlights the importance of being in good physical condition. AIMS: To take a first step at standardizing the administration of a job-related test to assess a person's ability to perform the physical demands of the core tasks of police work. The principal research questions were: are test scores related to gender, age and function and are test scores related to body mass index (BMI) and the number of hours of physical exercise? METHODS: Data of 6999 police officers, geographically spread over all parts of The Netherlands, who completed a physical competence test over a 1 year period were analysed. RESULTS: Women performed the test significantly more slowly than men. The mean test score was also related to age; the older a person the longer it took to complete the test. A higher BMI was associated with less hours of body exercise a week and a slower test performance, both in women and men. CONCLUSIONS: The differences in individual test scores, based on gender and age, have implications for future strategy within the police force. From a viewpoint of 'same job, same standard' one has to accept that test-score differences may lead to the exclusion of certain staff. However, from a viewpoint of 'diversity as a business issue', one may have to accept that on average, both female and older police officers are physically less tailored to their jobs than their male and younger colleagues.

Incidence and risk factors of running-related injuries during preparation for a 4-mile recreational running event.

OBJECTIVE: In this study, the incidence and the sex-specific predictors of running-related injury (RRI) among a group of recreational runners training for a 4-mile running event were determined and identified, respectively. DESIGN: Prospective cohort study. METHODS: Several potential risk factors were prospectively measured in 629 novice and recreational runners. They were observed during an 8-week training period for any running-related musculoskeletal injuries of the lower limbs and back. A running-related injury was defined as any musculoskeletal pain of the lower limb or back causing a restriction of running for at least 1 day. RESULTS: At least one RRI was reported by 25.9% of the runners during the 8-week observation period. The incidence of RRI was 30.1 (95% CI 25.4 to 34.7) per 1000 h of running exposure. Multivariate Cox regression showed that male participants were more prone to sustain a RRI than female participants (HR 1.4; 95% CI 1.0 to 2.0). No previous running experience was the most important risk factor in male (HR 2.6; 95% CI 1.2 to 5.5) and female (HR 2.1; 95% CI 1.2 to 3.7) participants. CONCLUSIONS: The incidence of running-related injuries in recreational runners preparing for a 4-mile running event is substantially high. Male and female participants have different risk profiles. Furthermore, the findings suggest that novice runners may benefit the most out of preventive interventions for RRI.

Motor skill performance of school-age children with visual impairments.

The aim of this study was to examine the performance of children with visual impairments (VI) aged 7 to 10 years on different types of motor skills. Furthermore, the association between the degree of the VI and motor performance was examined. The motor performance of 48 children with VI (32 males, 16 females; mean age 8y 10mo [SD 1y 1mo]) was assessed using the Movement Assessment Battery for Children (MABC). Their performance was compared with 48 children without VI (33 males, 15 females; mean age 8y 9mo [SD 1y 1mo]). Children with VI showed the poorest performance compared with peers without VI on unimanual speed, eye-hand coordination, catching, static balance, and dynamic balance while moving slowly. There was no significant difference between children with moderate and severe VI, except for bimanual coordination in 7- to 8-year-olds and eye-hand coordination in both the 7- to 8-year-olds and 9- to 10-year-olds, favouring the children with moderate VI. The poor performance compared with children without VI is related to vision, but the degree of the VI does not appear to relate to motor performance, except when associated with bimanual and eye-hand coordination. For children with VI, it seems very important to adjust the environmental context and task to enhance motor performance.

Different diagnostic tools in nonfunctional overreaching.

The current diagnosis of overreaching and overtraining is based on exclusion. In the present paper, four possible confirmative tools have been examined in three female speed skaters between 16 and 19 years old. A nonfunctional overreached (NFO) athlete, an athlete who was recovering from NFO and a healthy athlete were examined. The NFO athlete showed high stress and low regeneration levels at the Recovery Stress Questionnaire for Athletes. The recovering athlete showed a more favorable profile, although she still showed higher stress and lower recovery than the control athlete. On the Profile of Mood States, the NFO athlete showed an unfavorable profile. The control athlete showed the typical iceberg profile. The recovering athlete showed a profile similar to sedentary individuals. Results on a reaction time task showed decreased performance under pressure for the NFO but not for the control and the recovering athlete. Hormonal reactions to two maximal exercise bouts also differed between the three subjects with an overreaction after the second exercise bout of the NFO athlete as the most remarkable finding. The Recovery Stress Questionnaire for Athletes, reaction times and hormonal reactions to exercise showed to be possible tools that can be used in the diagnostic procedure.

The effect of high load training on psychomotor speed.

The purpose of the present study was to investigate whether overreached athletes show psychomotor slowness after a period of high load training. Fourteen well-trained cyclists (10 male, 4 female, mean age 25.3 [SD = 4.1] years, mean maximal oxygen consumption 65.5 [SD = 8.1] ml/kg.min) performed a maximal graded exercise test on a cycle ergometer, filled out two questionnaires and performed two tests of psychomotor speed before and after high load training and after two weeks of recovery training. A control group performed the two tests of psychomotor speed on the same occasions without changing physical activity levels. Five cyclists were classified as functional overreached, seven cyclists were classified as well-trained and two cyclists were excluded from analysis. Results showed no significant differences in psychomotor speed between the control, well-trained and functional overreached groups on the three measurements. A trend towards psychomotor slowness was found for the functional overreached compared to the control group after high load training. Additional research with more subjects and a greater degree of overload training is necessary to more conclusively determine if psychomotor speed can be used as an early marker for overtraining.

Interval endurance capacity of talented youth soccer players.

The purpose of this study, in which 113 talented youth soccer players (M = 16.0 yr., SD = 1.5), selected by their age and level of performance participated, was to investigate interval endurance capacity needed to play at the highest level of competition in the age-category 12 through 18. Multivariate analyses of covariance with factors of level of performance and age category showed that players ages 16 through 18 years outscored the players ages 12 through 15 years on the interval endurance capacity (p < .05). In both age categories, elite players outscored less skilled players (p < .05). In the age category 12-15 years, the elite players participated more in soccer training than less skilled players (p < .05), whereas less skilled players participated more in additional training than the elite players (p < .05). No differences were found for total training (p > .05). In conclusion, development of the interval endurance capacity seems crucial for a talented youth soccer player to be successful.

Development of the interval endurance capacity in elite and sub-elite youth field hockey players.

OBJECTIVES: To gain more insight into the mechanisms that underlie the development of interval endurance capacity in talented youth field hockey players in the 12-19 age band. METHODS: A total of 377 measurements were taken over three years. A longitudinal model for interval endurance capacity was developed using the multilevel modelling program MLwiN. With the model, scores on the interval shuttle run test can be predicted for elite and sub-elite male and female field hockey players aged 12-19 years. RESULTS: A polynomial model of order 2 adequately represents development of the test scores over time. The fixed part of the model contains a different intercept and linear age term for boys and girls, and a common quadratic term; the random part of the model has a common level 2 variance and sex specific level 1 variances. The model was significantly improved by including differential effects of performance level for age and sex. A negative effect was found for percentage body fat, and positive effects for additional training and motivation. CONCLUSIONS: During adolescence, both male and female elite hockey players show a more promising development pattern of interval endurance capacity than sub-elite youth players. Percentage body fat, additional training hours, and motivation influence this development. However, differences between the individual players are still considerable.

Evaluation of the reliability of two field hockey specific sprint and dribble tests in young field hockey players.

OBJECTIVES: To determine the reliability of two field hockey specific tests: the shuttle sprint and dribble test (ShuttleSDT) and the slalom sprint and dribble test (SlalomSDT). METHODS: The shuttle sprint and dribble performances of 22 young male and 12 young female field hockey players were assessed on two occasions within 4 weeks. Twenty one young female field hockey players took part in the slalom sprint and dribble test twice in a 4 week period. The ShuttleSDT required the players to perform three 30 m shuttle sprints while carrying a hockey stick alternated with short periods of rest and, after a 5 minute rest, three 30 m shuttle sprints alternated with rest while dribbling a hockey ball. The SlalomSDT required the players to run a slalom course and, after a 5 minute rest, to dribble the same slalom with a hockey ball. RESULTS: There were no differences in mean time scores between the two test sessions. The mean differences were small when compared with the means of both test sessions. With the exception of the slalom sprint time, zero lay within the 95% confidence interval of the mean differences indicating that no bias existed between the two measurements. With the exception of delta shuttle time (0.79), all intraclass correlation coefficient values for the ShuttleSDT, met the criterion for reliability of 0.80. Intraclass correlation coefficient values for SlalomSDT were 0.91 for slalom sprint time, 0.78 for slalom dribble time, and 0.80 for delta slalom time. CONCLUSIONS: ShuttleSDT and the SlalomSDT are reliable measures of sprint and dribble performances of young field hockey players.

The discriminative power of the Interval Shuttle Run Test and the Maximal Multistage Shuttle Run Test for playing level of soccer.

AIM: The purpose of this study was to examine the discriminative power of the recently developed Interval Shuttle Run Test (ISRT) and the widely used Maximal Multistage 20 m Shuttle Run Test (MMSRT) for soccer players at different levels of competition. The main difference between the tests is that the exercise mode of the ISRT is not continuous but intermittent. Instead of 60 s of running per stage in the MMSRT, 30 s of running are alternated with 15 s of walking, twice per stage. METHODS: Comparative study: within a 2-week period, 81 male soccer players at the Dutch premier league professional, premier league and 3rd division amateur levels performed the ISRT and the MMSRT. The total number of runs was scored for both tests. RESULTS: Only the ISRT distinguished between levels of competition. In general, the ISRT correlated moderately with the MMSRT for players of different levels of competition (rP: 0.52-0.83). CONCLUSIONS: In contrast to the MMSRT, the ISRT shows discriminative power for soccer players at different levels of competition supporting the validity of the ISRT for measuring endurance in a more soccer-specific way. As a result of the intermittent character of the ISRT the energetics of the ISRT and the MMSRT are not closely related.

Development of the Tactical Skills Inventory for Sports.

Purpose of this study, in which 19 trainers and 415 competitive youth field hockey and soccer players (M age=15.9, SD=1.6; 283 boys and 132 girls) selected by their age, sex, and performance status participated, was to develop a practical, reliable, and valid measure of tactical skills in sports. With trainers, 34 questions were formulated involving tactical skills. Factor analysis yielded the Tactical Skills Inventory for Sports. Scales were labeled Positioning and Deciding, Knowing about Ball Actions, Knowing about Others, and Acting in Changing Situations, covering all aspects of tactical skills regarding Declarative versus Procedural knowledge and Attack and Defense. Internal consistency and test-retest measures for reliability (except Knowing about Ball Actions) were within acceptable limits. Elite players scored better than nonelite players, supporting construct validity. The inventory is suitable for measuring tactical skills in youth field hockey and soccer players in sports practice.

Precision, comfort and mechanical performance of the Quadriso-tester, a quadriceps force measuring device.

The mechanical performance, repeatability and comfort of the Quadriso-tester, which assesses isometric knee extensor muscle strength, were examined. Twenty healthy subjects and 20 patients treated for unilateral anterior ligamenta cruciata insufficiency were tested. Intra-rater repeatability was determined by the testing and retesting of subjects and calculation of the intra-class correlation coefficient and the mean difference between test and retest values. The comfort level was determined a questionnaire. Measuring time was recorded, and the relationship between knee angle and extension moment was plotted. Strength and stiffness were determined using the finite element method. Intra-rater repeatability was high; the intra-class correlation coefficient of the right and left leg was 0.90 and 0.91, respectively; the coefficient of variation was 6.4 and 6.0%, respectively. The median comfort score of the healthy subjects was 7, and that of the patients was 9. Measuring time remained within 30 min. Misalignment of the knee and sidebar axis disturbed the relationship between knee angle and extension moment Strength and stiffness were higher than required. In conclusion, the Quadriso-tester is a comfortable and fast device to determine quadriceps force with a high repeatability. The knee and sidebar axis should be well aligned.