In the past three blogs, we explored the role of VALD technology in football, from jumping metrics to return-to-sport testing. Now, it’s time to shift the spotlight to one of the most talked-about muscle groups in the game: the hamstrings.
We’ve all read the literature. The connection between high-speed running, sprinting actions, and hamstring injuries is well documented. In elite football, hamstring strains are among the most common non-contact injuries, often occurring during acceleration, max sprinting, or late-game fatigue.
But here’s the twist—have you ever tested your own backyard?
We did. Across three different football academies, we collected internal injury data to better understand what’s really happening. The results were surprising: in two of the youth clubs, quadriceps injuries were actually more frequent than hamstring injuries. Only one club followed the expected pattern, with hamstring issues leading the list.
We collect the data with Ultrax software for the whole period. If you are interested what Ultrax can do, check it out here on the link: https://www.ultrax.ai/science-hub/.
So, what does this mean?
While we shouldn’t ignore the hamstrings, we also can’t afford to follow the literature blindly without testing and understanding our own context. However, one thing remains clear—we need to assess hamstring strength, particularly eccentric strength, and build robust training protocols to mitigate risk and improve performance.
Eccentric Strength: The Bigger Picture
When we talk about eccentric loading in football, it’s not just about Nordics or hamstrings. Eccentric strength is involved in nearly every high-intensity action: sprinting, braking, changing direction, kicking, and landing. These actions expose the body to forces up to 6–8 times bodyweight. The ability to control and absorb (produce :D) those forces is critical—not just for performance, but for injury prevention.
Eccentric Contractions, Testing & Variables in Football
2. Eccentric Strength Tests
When assessing eccentric hamstring strength, the Nordic Hamstring Test remains a cornerstone. It’s simple, reliable, and provides clear data—especially when paired with technologies like the VALD NordBord. While several tests can provide additional insight into eccentric function (like the ones listed below), the Nordic is often the most accessible and repeatable option for football teams across all levels.
Here are some of the tests that can complement Nordic strength assessments:
- Mid-Thigh Pull (MTP): Measures peak force and rate of force development (RFD) in the early contraction phase (100–150ms)
- Run-Specific Isometric Test (RSIT): Tests isometric strength at joint angles that simulate sprint mechanics
- Nordic Hamstring Test: Evaluates eccentric peak force, inter-limb asymmetry, and fatigue effects over time
- Braking Phase_ Force Plate : Horizontal deceleration capacity and braking impulse
- Change of Direction (COD) Test: Tracks deceleration and asymmetry pre-COD
- Eccentric Utilization Ratio (EUR): Compares CMJ and Squat Jump to reveal reliance on stretch-shortening cycle
Why and When to Test Nordics?
In professional football settings, we recommend using the Nordic Hamstring Test:
- At the start of the preseason as part of a larger diagnostic battery
- Multiple times in the first 2–3 weeks to establish a strong baseline
- Regularly during the in-season (e.g., once per week or every 10–14 days) for monitoring trends and identifying outliers
By establishing a player’s “normal range” during the preseason, teams can later detect meaningful deviations that could signal fatigue, injury risk, or under-recovery.
Tracking Change: Using CV and SWC
Once baseline values are collected, we can monitor weekly changes using:
- Coefficient of Variation (CV): Measures day-to-day or week-to-week variability in testing
- Smallest Worthwhile Change (SWC): The smallest change in value that’s likely to be meaningful (often 0.2 × between-player SD)
Example:
Let’s say we test 4 players during the preseason:
If Player C later records a force of 355N, that would exceed their SWC and signal a potential red flag, especially if combined with soreness, lower sleep scores, or increased fatigue.
From Numbers to Readiness: Nordic + COMBINATORIX
This is where things get exciting. Nordic results don’t exist in a vacuum—they can be combined with other readiness metrics to form a more holistic player profile.
For example, you can calculate a Z-score or composite readiness index based on:
- Max force in the Nordics
- Freshness index (subjective collected data)
- Pain status or soreness
- Sleep duration or quality
This creates a COMBINATORIX-style readiness score, which helps practitioners determine if the player is “ready to go” or needs modification—especially in high-risk weeks. In many professional clubs, Nordic testing is:
- Run weekly on MD+3, often before small-sided games
- Used as part of an introductory training session early in the week
- Tied to GPS or match load to interpret eccentric recovery demands
Of course, this starts to blur the lines between monitoring and periodisation, but the key idea is simple:
Know your players’ baseline. Monitor weekly. Use data to adapt.
Integrating GPS deceleration data with assessments of eccentric hamstring strength, such as the Nordic Hamstring Test, offers a approach to monitoring and enhancing player performance in football. However, accurately correlating these datasets presents challenges, particularly due to the difficulty in determining which leg bears the brunt of deceleration forces during analysis. This complexity underscores the need for further research to refine these methodologies.
Deceleration actions in football are notably demanding. Research by Harper et al. highlights that decelerations can impose forces exceeding 9 times body weight on players . Such substantial forces not only elevate the risk of injury but are also associated with declines in performance levels.
Advanced analytical techniques, including machine learning and random forest models, have been employed to explore the relationship between deceleration patterns and soft tissue injuries. For instance, studies have demonstrated that variables like the number of decelerations can serve as significant predictors of injury risk. In one study, the number of decelerations had the highest predictive power for injuries compared to other variables, emphasizing the importance of monitoring this metric.
These insights prompt a reevaluation of training drills, especially those conducted close to match days. Common practices on MD-1 and MD-2 involve 8v8 to 11v11 games in medium-sized spaces to manage player load. However, such drills often result in increased acceleration and deceleration actions. The available space allows players to reach higher speeds, necessitating greater deceleration forces. Additionally, the reduced area leads to more frequent ball interactions, thereby intensifying the drills.
Implementing constraints like limiting touches or introducing tactical objectives such as pressing or immediate ball repossession can further elevate the intensity. These modifications, while beneficial for tactical preparation, may inadvertently increase the physical demands on players, particularly concerning deceleration stresses.
Back to the Nordic Test
All of this brings me back to the Nordic Hamstring Test—not just as a baseline screening tool, but as a regular monitoring method for eccentric hamstring strength throughout the season.
In previous content, I’ve talked about microdosing strength and optimizing warm-ups for performance and injury prevention (you can read more on: https://www.ultrax.ai/uncategorized/hidden-testing/). Now, I’d like to take it a step further and propose how the Nordic test can be smartly integrated into the weekly football routine.
I believe there is real value in using the Nordic test on MD-2 or MD-1, either before or after the training session, to observe how recent training loads have impacted hamstring function. Personally, I lean toward testing after the session, as it gives us a clearer picture of fatigue or recovery status.
A few weeks ago, we ran a small experiment to explore this idea further.
We tested a player—one of my students and a former professional—who has a history of two ACL injuries. He doesn’t train at a professional intensity anymore, but he’s active and familiar with the load. We used the VALD NordBord to measure his eccentric hamstring strength, and here’s what happened:
- Nordic Hamstring Test after warm-up (pre-training): → ~350 ± 20N
- Then we applied an RSA protocol: → 1 set of 6 repetitions of 2x20m sprints (including one change of direction), with 30 seconds rest
- Nordic Hamstring Test after RSA protocol (post-training): → 15% drop in peak force
That kind of drop—especially in someone not exposed to regular high-intensity loads—speaks volumes. It suggests that even short bursts of high-speed activity, sprinting, and deceleration can significantly fatigue the hamstrings and reduce their capacity to produce eccentric force.
Now, we’re taking it a step further with a new monitoring project in a women’s football club.
For the next 2–4 weeks, we’ll test players:
- Before and after training sessions
- Using CMJ (Countermovement Jump) and the Nordic Hamstring Test
- While also tracking:
The goal is to understand how different training formats affect neuromuscular readiness, fatigue, and eccentric capacity in real-world team sport environments.
By collecting this data consistently, we hope to build a smarter system of load management—one where the Nordic test isn’t just a pre-season screening tool, but a weekly pulse-check that helps us align training demands with each athlete’s readiness and resilience.
Let’s see what the data reveals. One thing is certain: the more we integrate strength diagnostics with contextual understanding of training (e.g., drill design, session intensity, recovery status), the closer we get to real performance intelligence.
