PhD Pinboard: Maximising the Impact of Fitness Testing in Elite Soccer
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- May 14
- 10 min read
This PhD Pinboard article by Nikolaos Asimakidis bridges the gap between fitness testing research and practice in elite soccer, with a focus on test selection, data interpretation, and impactful data visualisation.
I’m Nikos Asimakidis, a sports scientist with experience in Greece, Germany, and England. I’m currently working as a Sports Scientist at Ipswich Town FC Academy while completing my PhD at Middlesex University London.
My PhD research focuses on something every soccer practitioner is familiar with, yet rarely looked in depth: fitness testing.
Fitness testing can lay the foundation (1) for:
Performance enhancement
Injury risk reduction
Talent identification
However, with so many fitness tests available, and even more emerging thanks to technological advancements, practitioners face growing uncertainty about which ones to choose. Meanwhile, the increased accessibility of sophisticated equipment in applied settings has led to an overwhelming volume of data, resulting in what feels like a “data tsunami”. Yet more data doesn’t guarantee better decisions.
For fitness testing to have real impact, results must be clearly reported to a range of stakeholders, such as coaches, players, and medical staff, in ways that are easy to understand and act upon. Effective data visualization is key for turning numbers into meaningful insights (2).
The aim of this project is to increase the real-world impact of fitness testing by focusing on two key areas:
Selecting assessments that are practically relevant and reliably detect meaningful changes
Presenting testing results in ways that support decision-making across departments
In this blog post, I’ll share insights from that journey, aspiring to help practitioners unlock the full potential of fitness testing, maximizing both its value and the resources invested in it.
The Story Behind This PhD Project
Throughout my career, I’ve seen myself at the intersection of research and practice. My Master’s thesis, which examined change of direction asymmetries in relation to biological maturation (3), helped me prepare for the academic demands of a PhD. As an international practitioner, this embedded PhD role provided me with a unique opportunity to enter the competitive UK job market, which is particularly challenging post-Brexit, while enabling me to produce real-world, impactful research.
At Ipswich Town FC Academy, fitness testing is an integral part of our evidence-informed approach to player development. However, when I searched the literature for guidance, I found no comprehensive overview of fitness testing protocols in elite soccer. This gap sparked the first stage of my PhD: a deep dive into the scientific literature to map out the current state of knowledge.
After hundreds of hours synthesizing the existing literature, this work culminated in what I call the “fitness testing trilogy”— three systematic reviews that identified the most commonly used tests and outcome variables in elite male soccer.
To bridge the gap between theory and practice (4), I conducted a practitioner survey exploring how fitness testing is currently applied in elite soccer.
Building on these theoretical and practical insights, I undertook a season-long study investigating the reliability and sensitivity of the key tests identified earlier.
Through my daily work at the club, the importance of data visualization became increasingly clear. This opened the door to an under-explored but critical question: how do we present data in ways that multidisciplinary staff can actually understand, value, and use? It also provided a valuable professional development opportunity: mastering software like Microsoft Power BI and R that are now in high demand in applied sports science.
Key Findings
What the sports science literature says
As expected given the global popularity of soccer, the systematic reviews identified a vast number of relevant studies (5–7). The findings revealed a strong emphasis on:
Power (127 studies)
Aerobic fitness (124 studies)
Linear speed (119 studies)
Strength (115 studies)
In contrast, the change of direction (COD) (53 studies) and repeated sprint ability (RSA) (27 studies) received considerably less attention.
Figures 1, 2, and 3 provide a visual summary of the findings by illustrating the number of different tests identified for each physical quality, the most frequently used assessments, as well as normative and reliability data.
The reviews also highlighted emerging trends in test selection over the past decade, including a growing use of:
Single-leg countermovement jump (SLCMJ)
30-15 Intermittent Fitness Test
Beyond identifying testing frequency, the reviews provided normative values for widely used protocols, offering practitioners a benchmark to contextualize and compare player performance.
However, substantial methodological inconsistencies were noted across studies, including variability in equipment, protocol design, and calculation methods. For example, in countermovement jump (CMJ) testing, studies have used a variety of equipment, such as force plates, photoelectric systems, and jump mats, each of which calculates jump height differently (e.g., take-off velocity vs. flight time method) (8).
Similarly, linear speed testing varied widely in terms of timing gate brands, starting distances, test surfaces and even whether the tests were conducted indoors or outdoors.
These methodological discrepancies compromise the direct comparability of results, requiring practitioners to interpret normative values with caution, and use only those derived from identical protocols. They also highlight the need for greater standardization if we want robust comparable data across teams and contexts.
What practitioners are actually doing
The first survey study explored how fitness testing is implemented in applied settings (9), focusing on four key areas:
test selection
test administration
data analysis
data reporting
Figure 4 illustrates the most commonly assessed physical qualities, along with the three most frequently reported tests for each.
Consistent with the findings from the systematic reviews, practitioners placed a greater emphasis on assessing strength, aerobic fitness, power, and linear speed.
Interestingly, the isometric mid-thigh pull (IMTP) emerged as the most commonly used strength test, despite appearing in only one study in the systematic review. This reinforces how advances in practice do not always coincide with the current research literature. In this case, and the growing interest in isometric training and testing may explain the increasing adoption of IMTP by practitioners (10,11).
Some other notable findings were:
Time constraints and congested match schedules were major barriers to fitness testing, leading many practitioners to adopt hybrid approaches that combine formal testing days with in-training data collection.
Microsoft Excel was the main software for data analysis and visualization, although Power BI is gaining popularity for data visualization.
Less than 40% of practitioners accounted for measurement error when interpreting results, raising concerns about whether observed changes truly reflect “real” performance improvements (12).
Not all tests are created equal
One important caveat that everybody should keep in mind: frequency of use does not imply the superiority of a test. Just because a test is widely used doesn’t mean it’s suitable for tracking meaningful performance changes over time.
This realization led me into the next stage of my research — evaluating the diagnostic accuracy of commonly used assessments, specifically examining the reliability and sensitivity through the signal-to-noise ratio (SNR). This study has been accepted for publication in the International Journal of Sports Physiology and Performance.
The CMJ, Nordic hamstring strength, 10-m sprint, and Bronco tests proved both reliable and sensitive, with over 60% of players showing changes that exceeded natural measurement variability. In contrast, SLCMJ jump height and IMTP relative peak force showed lower sensitivity and reliability, with fewer than 60% of players achieving meaningful changes, raising concerns for individual and group-level monitoring (Figure 5).
Additionally, while using the mean of multiple trials generally produced slightly better reliability, both approaches yielded comparable results overall.
Visualization methods that work
For the final stage of my PhD project, I conducted an international survey study investigating the reporting and visualization needs and preferences of fitness testing data, with input from 145 elite soccer practitioners across 35 countries.
Although the study is currently under peer review and full results cannot yet be disclosed, it will contribute to developing more effective reporting strategies that enhance data-informed decision-making and foster collaboration across multidisciplinary teams. We will update the results here when published!
How can we apply these findings in practice?
While no single PhD project can address all the challenges in fitness testing, I hope that this work represents a practical step forward. The “fitness testing trilogy” and the survey study on current testing practices, form a comprehensive, state-of-the-art resource to support practitioners in making informed decisions about test selection.
Here’s my first key message for practitioners: don’t just choose tests simply because they’re popular. Instead, prioritize those with strong diagnostic value and relevance to your specific context. In this sense, reliability is a fundamental component of fitness testing that all practitioners take into account. In its absence, we risk acting on misleading data and misinterpreting noise as progress.
Tests like the CMJ, Nordic hamstring strength, 10-m sprint, and Bronco tests appeared well suited for reliable assessment and longitudinal tracking. Still, wherever possible, practitioners should conduct in-house reliability checks to confirm that these tests perform consistently within their own environment. In doing so, organizations can avoid wasting resources on processes that won’t move the needle, and instead focus on fewer, high-quality tests that truly inform decision-making.
Furthermore, in time-constrained environments like elite soccer, embedding performance assessments into training offers a practical and efficient way to increase data collection (13). For instance, CMJ assessments can be incorporated into power-focused gym sessions, while linear sprint tests can be performed at the end of speed warm-ups.
This approach enables frequent performance monitoring without disrupting training flow.
Future research should explore how to optimize these processes for maximum reliability with minimal interference.
To this end, wearable technologies, such as inertial measurement units (IMUs) hold significant potential to enhance “invisible” data collection, provide deeper insights, and bridge the gap between lab and field testing (14). But testing is only as valuable as how we interpret and communicate the results.
Data visualization is no longer a “nice to have”. It’s an essential skill for modern sports scientists. To maximize the impact of your testing information, it is essential to tailor the level of reporting detail to your audience: coaches may not need error bars or confidence intervals, but they will value clear visuals that communicate the key message at a glance.
That’s how we move from simply testing athletes to truly impacting their development.
To stay ahead of the curve, practitioners should continuously enhance their ability to understand, analyze, and present data, enabling them to adapt to the ever-evolving demands of elite sports.
Final Reflections
Looking back, this PhD journey was far from easy. Balancing the demands of a high-performance environment alongside academic research challenged me in ways I never expected. Nevertheless, it was incredibly rewarding.
Beyond the privilege to contribute to the scientific knowledge, it gave me the opportunity to grow, connect with brilliant minds, and learn from both practitioners and academics who have shaped my thinking.
Most importantly, it reaffirmed my belief that research should never exist in isolation. When grounded in real-world problems, it has the power to drive meaningful change and directly enhance practice.
I’m always open to sharing ideas or connecting with others working in this space. Feel free to reach out on LinkedIn (Nikolaos Asimakidis).
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Frequently Asked Questions (FAQs)
What were the most commonly used fitness tests identified in elite male soccer?
The most commonly used fitness tests in elite soccer were the IMTP (strength), 30-15 IFT (aerobic fitness), CMJ (power), 10-m sprint (linear speed), and 505 test (change of direction).
Why is test reliability so important in fitness monitoring?
Reliability is the backbone of meaningful performance assessment. Without it, distinguishing real progress from normal day-to-day variability becomes difficult, compromising the validity of conclusions drawn from the data. Reliable tests allow practitioners to make more confident, data-informed decisions about training, recovery, and player management.
What role does data visualization play in effective fitness testing?
Effective data visualization bridges the gap between numbers and actionable insights. Intuitive visuals help key stakeholders quickly grasp testing data without needing technical expertise, facilitating faster decisions. After all, humans think in pictures.
What are some common challenges in comparing fitness testing results across studies?
A major challenge is the lack of standardization across studies. Differences in equipment, testing protocols, and calculation methods can influence results, making direct comparisons difficult. To enable accurate benchmarking, greater consistency in testing procedures is essential.
References
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7. Asimakidis ND, Bishop C, Beato M, Turner AN. Assessment of Aerobic Fitness and Repeated Sprint Ability in Elite Male Soccer: A Systematic Review of Test Protocols Used in Practice and Research. Sports Med [Internet]. 2025 Apr 12 [cited 2025 May 1]; Available from: https://link.springer.com/10.1007/s40279-025-02188-4
8. Xu J, Turner A, Comfort P, Harry JR, McMahon JJ, Chavda S, et al. A Systematic Review of the Different Calculation Methods for Measuring Jump Height During the Countermovement and Drop Jump Tests. Sports Med. 2023 May;53(5):1055–72.
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13. Leduc C, Weaving D. Invisible Monitoring for Athlete Health and Performance: A Call for a Better Conceptualization and Practical Recommendations. International Journal of Sports Physiology and Performance. 2025;1–5.
14. Marques JB, Sideris V, Whiteley R, Read PJ, Gomes MM, Santiago PRP. Wearable technology identifies differences in change of direction kinetics and kinematics in soccer players with a history of anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc [Internet]. 2025 [cited 2025 Apr 21]; Available from: https://esskajournals.onlinelibrary.wiley.com/doi/10.1002/ksa.12679
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