Optimising fitness testing in elite soccer: from test selection to effective data visualisation

Fitness testing is a fundamental component of the physical development process in elite soccer, enabling practitioners to objectively assess players’ athleticism and monitor training adaptations. To maximise its effectiveness in applied settings, it is essential to employ tests that are both practical and diagnostically accurate, ensure robust data analysis, and present results to various stakeholders in an intuitive and impactful manner. Consequently, this thesis aimed to: 1) identify the most relevant tests used in both research and applied practice, 2) evaluate the reliability and seasonal sensitivity of a soccer-specific fitness testing battery, and 3) establish evidence-informed data reporting guidelines based on the needs and preferences of key stakeholders. The systematic reviews (Chapters 2-4) provided a comprehensive investigation of the fitness testing landscape in elite soccer literature, outlining well-established and emerging protocols, normative values, and reliability data. The findings revealed a predominant research focus on power (127 studies), aerobic fitness (124 studies), linear speed (119 studies), and strength (115 studies). Conversely, the assessment of change of direction (COD; 53 studies) and repeat sprint ability (RSA; 27 studies) received much less attention. Among aerobic fitness assessments, incremental treadmill testing was the most commonly used (45% of studies), followed by Yo-Yo Intermittent Recovery Test 1 (YY1R1) (18%) and Yo-Yo Intermittent Recovery Test 2 (YYIR2) (8%). Nevertheless, field-based aerobic tests accounted for 74% of the identified assessments, possibly attributed to their practicality and ecological validity. Countermovement jump (CMJ) was the predominant method for power assessment (78% of studies), while linear speed was most frequently evaluated using 10m (61%) and 20m (40%) sprints. Strength testing was primarily performed using isokinetic knee strength assessments, with 50% of studies evaluating extension and 48% assessing flexion. The systematic reviews also highlighted a growing use of tests such as the Nordic hamstring strength test, isometric hip adductor strength test, single leg countermovement jump (SLCMJ), 30-15 Intermittent Fitness Test (30-15 IFT), and submaximal field aerobic assessments over the past decade. In addition to identifying testing prevalence, the reviews provided normative values for widely used assessments, offering reference values that assist researchers and practitioners in contextualising and comparing player performance. Nevertheless, substantial methodological inconsistencies were observed across studies, including variability in testing equipment, protocol design, and calculation methods, limiting the direct comparability of reported values. Hence, this discrepancy highlights the need for standardised testing procedures to enhance the applicability and comparability of results. Another notable finding in the reviews was the scarcity in reporting reliability data, particularly for between-day reliability. In fact, only a small proportion of the identified studies reported reliability metrics for COD (34%), linear speed (30.6%), power (27%), RSA (18%), strength (13%), and aerobic fitness (9.6%). The lack of reliability research in elite soccer hinders the ability of researchers and practitioners to determine the diagnostic accuracy of key performance tests and their effectiveness in monitoring longitudinal player progress. Study 1 investigated the real-world implementation of fitness testing in elite soccer by surveying 102 practitioners from professional leagues across 24 countries. The study focused on four key areas: 1) testing selection, 2) testing implementation, 3) data analysis, and 4) data reporting. Strength (85%) and aerobic fitness (82%) were the most frequently assessed physical qualities, followed by power (78%), linear speed (71%), COD (52%), and RSA (32%). The CMJ (92%), 10m sprint test, and 505 test were the predominant assessments for power, linear speed, and COD, respectively, which is consistent with the findings of the systematic review. However, there were notable differences between research and applied practice for strength and aerobic fitness testing. Specifically, the isometric mid-thigh pull (IMTP) was widely used by practitioners (35%) for strength evaluation, despite its limited representation in elite soccer literature. Similarly, the 30-15 IFT was the most frequently employed aerobic fitness test, contrasting with the predominant use of incremental treadmill testing in the scientific literature. Fitness testing was primarily conducted in pre-season (88%), with practitioners reporting time constraints and congested competitive schedule as the most significant barriers to its implementation. To address these challenges, 45% of practitioners adopted a hybrid testing model that combined dedicated testing days with integrated assessments during training sessions. Regarding data analysis and visualisation, Microsoft Excel was the main software, with Microsoft Power BI becoming increasingly popular for data visualisation. Data analysis approaches varied, with 44% of practitioners utilising a combination of best and mean scores. While comparison to previous performance was the main method for interpreting fitness test results (89%), only 38% of practitioners accounted for measurement error. Overall, these findings reinforce the importance of integrating scientific rigour with applied feasibility to ensure that fitness testing in elite soccer remains both methodologically robust and practically viable to inform decision-making. To address the need for robust and practically relevant fitness testing, Study 2 evaluated the reliability and seasonal sensitivity of a fitness testing battery in elite youth players. The fitness testing battery included the CMJ, SLCMJ, IMTP, Nordic hamstring strength test, 10m sprint test, 505 test, and the Bronco test. A test-retest evaluation, separated by a one-week interval, was conducted during the preseason, with follow-up assessments at midseason and end of season. Fifteen out of 20 outcome variables demonstrated lower coefficients of variation (CV) when the mean of multiple trials was used, although both mean and best trial approaches returned comparable results, indicating that neither method was clearly superior. Most variables had CV values below 5%, with exceptions including SLCMJ left, SLCMJ right, Nordic left, change of direction deficit (CODD) left, and CODD right (CV: 5–10%). CMJ mean eccentric force showed the lowest CV (0.55-0.59%), whereas CODD right had the highest (7.80-9.60%). Relative reliability was moderate to excellent across all metrics (intraclass correlation coefficient [ICC]: 0.55–0.997), with 17 out of 21 variables demonstrating good reliability. 505 right and left (ICC: 0.56-0.62) and CODD left and right (ICC: 0.55-0.66) were the outcome variables demonstrating moderate reliability. Sensitivity analysis revealed that 13 out of 20 variables showed higher signal-to-noise (SNR) values when the mean was used, with SNR ranging from 0.93 to 3.08. The IMTP relative peak force displayed the lowest sensitivity (0.93–0.98), while CMJ mean eccentric force demonstrated the highest (2.88–3.08). Notably, 20 out of 21 variables had an SNR > 1.0, with IMTP relative peak force being the only exception. At the individual level, the proportion of athletes exhibiting an SNR > 1 varied from 46% to 88%, with CMJ mean eccentric force, CMJ peak power, and Nordic hamstring peak force right displaying the highest sensitivity (75%–88%), and the SLCMJ left the lowest (46%). Performance changes across the season were further quantified using Hedges’ g. The 505 COD completion time, CODD, and Nordic hamstring strength demonstrated the largest improvements (effect size [ES]: -0.69 to -1.03 for the 505 test, -0.62 to -1.04 for CODD, and 0.84 to 0.99 for Nordic strength). In contrast, aerobic fitness remained stable from preseason to midseason (ES: -0.18), before showing a moderate decline from midseason to end of season (ES: 0.59). Recognising the pivotal role of results’ communication in enhancing the impact of fitness testing, the final study (Study 3) investigated how fitness testing data can be most effectively reported and visualised to support decision-making in elite soccer environments. Specifically, the survey examined preferences regarding report content and the interpretability of various data visualisation formats. A total of 145 elite soccer practitioners from 35 countries completed the survey. The findings indicated a balanced focus on both individual and team performance (42.8%). The majority of practitioners (91%) prioritised tracking changes in player/squad performance over time, compared to benchmark (61%) and position-specific comparisons (58%). Raw scores were the most preferred data format (62.1%), followed by standardised (37.2%) and composite scores (23.5%). In terms of data visualisation, participants highly valued the use of interactive dashboards (91%) and traffic-light systems (77.2%). Quadrant charts were endorsed for their interpretability by 87.6% of participants, acknowledging their effectiveness in player profiling and training prescription. Bar charts (77.2%) were the most preferred format for visualising squad-level testing results, whereas line charts (51.7%) were the most favoured format for illustrating the longitudinal progress of a player. Radar charts (59.3%) were preferred over bar charts for comparing a player’s performance to the group average, as they provide a holistic and quick view of strengths and weaknesses across multiple metrics. Interestingly, the inclusion of uncertainty indications such as error bars and confidence intervals yielded mixed opinions among practitioners. While 52.3% of participants supported their use, concerns were raised about their interpretability among staff with limited statistical exposure and the potential for visual clutter. Collectively, the findings from Study 3 contribute to the development of evidence-informed reporting practices that improve the usability of fitness testing data and facilitate stronger collaboration across multidisciplinary teams. In conclusion, this thesis presents a robust framework for enhancing fitness testing practices in elite soccer. Through a combination of systematic reviews, survey-based research, and evaluation of test psychometric properties, this work bridges the gap between academic rigour and practical feasibility. By prioritising tests with high reliability and sensitivity, practitioners can more effectively allocate time and resources to assessments that provide meaningful insights into athletic performance. Beyond test selection and implementation, this thesis suggests evidence-informed data reporting methods to enhance the clarity, impact, and accessibility of fitness testing data, while also highlighting the critical need to upskill practitioners in data literacy and visualisation to meet the evolving demands of high-performance sport.

Name dc:type.qualificationname

PhD

Level dc:type.qualificationlevel

PhD thesis

Grantor dc:publisher.institution

Middlesex University

Year dc:date.issued

2025

Author dc:creator

• Asimakidis, N.

Identifier

oai:repository.mdx.ac.uk:368359

OAI identifier oai:identifier

oai:repository.mdx.ac.uk:368359