Part Three:
Application of the Injury Reduction Framework
Keeping athletes strong, resilient, and ready to play is one of the main priorities for any performance coach or exercise professional. When key players are sidelined, it doesn’t just affect their own development, it can affect the outcome of games – and even entire seasons. Practitioners must proactively make minimising injury occurrence a central focus of their work, ensuring athletes remain healthy, available for selection, and performing at their best throughout the season.
To achieve this, coaches should adopt a multi-faceted and integrated approach. In Part 1 of this series, we discussed a systematic five stage injury reduction process designed to create an individualised, bespoke injury reduction programme which forms part of the athletes normal training schedule. In Part 2, we described how this injury reduction framework might be implemented in men’s soccer, specifically using hamstring injuries as a model. In this penultimate part of the series, we will discuss application of the next two stages of the injury reduction framework – namely, identification of injury risk factors and identification of specific athlete injury risks – and discover why teams who adopt Apollo can see significant reductions in time-loss injuries over the course of a season.
We left Part 2 having identified the primary mechanisms of hamstring injury in men’s soccer. From this, practitioners are in a position to advance to the third phase of the injury reduction process: Identifying the intrinsic and extrinsic risk factors which are associated with hamstring injury occurrence.
Injury Reduction Stage 3: Hamstring Strains in Men’s Soccer – Injury Risk Factors
Here we have a breakdown of some of the primary risk factors which have been shown to contribute to hamstring injury in men’s professional soccer:
- Previous Injury
- Hamstring Strength
- Neuromuscular Control – Intermuscular & Intramuscular coordination
- Core Strength – Proximal control
- Running Mechanics
- Work Capacity & Fatigue Tolerance
- Playing Position
- Change to Training Programme
Let’s take a closer look at each of these risk factors, and explore how they can increase the prospect of a hamstring injury.
Previous Injury
The most significant risk factor for a footballer sustaining a hamstring injury is a history of previous hamstring injuries. Players with a history of having had one previous hamstring injury are over 33% more likely to sustain an injury than a player with no injury history. This raises an important point. Does this happen because the player already had an existing predisposition to hamstring injuries, or does having had a hamstring injury lead to some sort of maladaptation in the way the hamstring functions, which leaves it weakened in some way and therefore more susceptible to injury?
To answer this, studies have been conducted which show that previous injury can result in eccentric weakness in the hamstring, as well as reduced fascicle length and atrophy of the long head of the biceps femoris (BF). The most common site for hamstring injury has been identified as being the long head of the BF, therefore it follows that the combined effects of eccentric weakness, reduced fascicle length and atrophy of the long head of the BF, all of which have been found to be a consequence of previous injury, could lead to in increased risk of the player suffering a re-injury.
Separate studies have shown that footballers who have had a previous hamstring injury can also experience disrupted muscle activation, where the BF compensates for a lack of activation in the semitendonosus (ST). This increased activation of the BF could lead to it becoming overloaded to an extent which exceeds its functional capacity, causing it to fail.
So how can practitioners use the results of these findings to protect against future injury? These studies recommend that eccentric exercises, exercises which preferentially recruit the long head of the biceps femoris, and neuromuscular control exercises which reinforce appropriate muscle firing patterns, should all be incorporated into the rehabilitation programme of a player who has sustained a hamstring injury, in order to reduce the likelihood of re-injury occurring, and to mitigate this as an injury risk factor.
Hamstring Strength
Hamstring strength also plays a huge role in the ability of a player to avoid injury. Poor hamstring strength results in the forces being generated during sprinting surpassing the tolerance of the muscle-tendon unit of a weak hamstring, causing it to fail. To mitigate this injury risk, two important factors must be addressed. Firstly, it is vital that the hamstring strength of players is regularly monitored. Secondly, hamstring strengthening exercises should be incorporated into the weekly performance programmes of players, in order to ensure that they maintain the strength needed to support a healthy, functioning hamstring. To address this issue of functionality, recent contemporary thinking has started to look at the role that the hamstrings play during sprinting and high-speed running in a different way. A growing number of practitioners now advocate that during the late swing phase (when the majority of sprint related hamstring injuries occur), the hamstrings don’t actually lengthen eccentrically as previously thought, but instead primarily contract isometrically while the tendon stretches and recoils in an elastic response. This means that hamstring injuries may in fact occur because the muscles are not strong enough to maintain an isometric contraction in long length positions when they are being exposed to high levels of force, such as in a sprint action. For this reason, practitioners are increasingly incorporating long length isometric exercises into their hamstring injury reduction protocols.
Neuromuscular Control
Neuromuscular control can also influence hamstring injury. Firstly, in terms of intermuscular co-ordination, the muscles in the posterior chain which act as synergists to the hamstrings must function effectively to prevent the hamstrings from becoming overloaded.
Secondly, in terms of intramuscular coordination, it is vital that the muscles in the hamstring, particularly the BF and the ST, work in a specific, coordinated neuromuscular pattern. The BF is activated prior to and immediately after touchdown, whilst the ST is activated during mid and late front swing, which has been identified as being the point at which most hamstring injuries occur. The ST is more prone to premature acidification and to fatigue, and when this happens the BF compensates for any lack of ST activation and becomes overloaded. The problem is that the BF is not suited for force production in the distal range of movement during late swing phase, where the ST is normally active. This then puts it at risk.
This reflects two of the facts that we know about hamstring injuries in men’s soccer: firstly, that they occur towards the end of each half and are therefore associated with acute fatigue; and secondly that the majority of injuries occur in the BF. For that reason, a conclusion that we might come to is that a functionally balanced BF-ST unit is of major importance to injury reduction, and in order to protect the BF we may need to actually pay more attention to the function of the ST, specifically, its ability to withstand fatigue.
Core Strength
A further injury risk factor is the level of core strength and proximal control that a player has. The core muscles are used to modify the tilt of the pelvis during running, which in turn influences the length of the hamstring. An excessive anterior pelvic tilt places the hamstrings in a lengthened position, increasing tension on the muscle-tendon complex and making it more susceptible to overload. For that reason, it is important that players have a strong core and good proximal control if they are to avoid hamstring injury.
Running Mechanics
Core strength relates to a fifth hamstring injury risk factor, which involves the running mechanics of the player. An excessive forward trunk lean during sprinting induces an anterior pelvic tilt, which as we have just highlighted places the hamstrings in a lengthened position and increases the risk of a hamstring injury occurring. Hamstring injury is also associated with thoracic side bending during acceleration, and for that reason, it is important that practitioners ensure that their players are moving well with good, efficient running mechanics.
Work Capacity & Fatigue Tolerance
Player fitness can also be considered as being a risk factor for hamstring injury, and we have already explored two potential mechanisms which underpin this.
Firstly, it has been identified that hamstring injuries in soccer occur more frequently towards the end of each half, and that acute fatigue can cause the hamstrings to function in a less coordinated manner where the BF compensates for a fatigue-related lack of ST activation. Players with poor fitness levels are more likely to experience this breakdown in intramuscular coordination, resulting in greater injury risk.
Secondly, fatigue can also compromise lumbopelvic control, and when this happens it can negatively affect a player’s motor skills, causing them to adopt altered movement patterns. This change in the way that the player moves can place greater mechanical stress on the hamstrings, making them more vulnerable to injury. For this reason, it is important to ensure that players develop high levels of physical capacity to resist fatigue, maintain movement efficiency, and consequently to protect against potential injury.
Playing Position
Playing position can also influence the potential for hamstring injuries. Certain positions have greater sprint demands than others, for example, players in wide positions will sprint more than central defenders, resulting in an increased load on the hamstrings. We know that the majority of hamstring injuries are associated with the forces being produced during sprinting, therefore it is imperative that soccer players who play in positions with a high sprint component engage in hamstring injury reduction protocols, in order to ensure they are capable of coping with the greater physical demands associated with their position.
Change to Training Programme
Finally, any change to the players normal and established training routine can result in an increased risk of injury, with this having two potential mechanisms: overwork and under preparation.
Sudden, excessive and rapid spikes in training loads can stress the hamstrings beyond their current work capacity, and this is responsible for a large proportion of muscle injuries. Conversely, reducing training loads in an attempt to minimize training related injuries can be counterintuitive. Sustained periods of undertraining create players who are not adequately prepared to cope with the physical demands associated with competitive match play, which consequently leads to an increased risk of injury during games.
This process of identifying the specific risk factors associated with hamstring injury, and by extension understanding the underlying mechanisms which can potentially cause a hamstring to fail, is essential. It provides exercise professionals with the information they need to put training interventions into place which are designed to positively modify the hamstring, mitigate these identified risks, and thereby reduce the potential of a hamstring injury occurring. However, for these interventions to have a greater likelihood of being successful, each injury reduction protocol has to be individualised according to the unique profile of each athlete. This means that practitioners must evaluate the level of risk that each player has of sustaining an injury, which is the purpose of stage 4: Athlete screening.
Stage 4: Hamstring Strains in Men’s Soccer – Identify Specific Player Injury Risk
One of the central pillars of an effective injury reduction strategy is to have a comprehensive screening system in place which is designed to assess an athlete’s level of injury risk. If practitioners can establish the risk status of each individual athlete, it means that they can then plan their subsequent training programmes for that athlete with a higher degree of accuracy.
From our analysis of hamstring risk factors, we know that hamstring injuries can come from a number of different sources. This presents a significant challenge to the screening process, because a single test, performed in isolation, will only assess one particular aspect of injury risk. For that reason, a multivariate approach needs to be adopted, using a number of different tests, with each one designed to evaluate a specific risk factor. A comprehensive hamstring screening protocol may include any or all of the following:
Instrumented Nordic Hamstring Test
One of the proposed risk factors for hamstring injury is eccentric weakness, making eccentric force testing a commonly used screening tool. The Nordic Hamstring Test uses a force-measuring device that quantifies eccentric knee-flexor hamstring strength during the Nordic hamstring exercise. Players perform controlled Nordic lowers while the device records both peak and mean eccentric force, as well as identifying any asymmetry between the left and right leg. This test can provide coaches with multiple data points, including absolute force values, left/right limb asymmetry (with ≥10–20% commonly flagged as a potential problem), and load-time profiles to identify weakness or neuromuscular deficits. This test is regularly used to track the way that players are responding to eccentric strengthening programs.
Isokinetic Dynamometry (Concentric, Eccentric & Isometric Torque Testing)
Another identified risk factor is hamstring strength. The isokinetic test involves the tester using a clinical device that measures the concentric, eccentric and isometric peak torque values that the hamstrings are capable of producing across different joint angles and velocities. This provides practitioners with isolated strength profiles and hamstring:quadriceps ratios, which can be used for baseline profiling, post-injury clearance benchmarks, and identifying strength imbalances.
Ultrasound Muscle Architecture
Ultrasound imaging can be used to measure BF long head fascicle length and cross-sectional area. We have explored the impact that shorter fascicle length and smaller cross-sectional area can have on increased hamstring strain risk (especially with players who have a history of hamstring injury), therefore using ultrasound both to identify structural risk markers and to monitor training adaptations during rehabilitation can be a useful screening tool.
Passive Straight Leg Raise and Active Knee Extension Flexibility Tests
These clinical range-of-motion tests are used to assess hamstring length and tension in order to detect side-to-side ROM asymmetries or restricted tolerance.
Sprint Testing and High-Speed Running Analysis
The relationship between sprinting and hamstring injury is well established, making sprint testing a crucial part of the practitioners screening toolbox. Deviations from a player’s normal sprint profile, such as reduced top speed, slower acceleration, or asymmetrical split times can indicate hamstring weakness or pain-limiting effort.
Sprint Force–Velocity Profiling
As well as monitoring absolute speed times, sprint testing can also provide practitioners with insights into how players are actually applying force during high velocity movements. By using force plates, practitioners can establish a force-velocity profile for each player during sprint actions. Those players who demonstrate lower horizontal force production or reduced early-phase force expression might have posterior chain under-development and, therefore, increased sprint-related hamstring injury risk. The data from these tests can be used to prescribe targeted strength and technical sprint drills.
Video-Based Biomechanical Analysis
We have discussed how running mechanics can be a potential injury risk factor. For that reason, 2D and 3D analysis of sprinting technique, hip-trunk control, and late-swing mechanics using video software is another valuable screening tool. These systems allow coaches to inspect kinematics during late swing and terminal swing phases and identify any potential risks. For example, excessive anterior pelvic tilt, overstriding, or reduced knee flexion can increase strain on the BF. The findings from these tests can inform technique drills, core and hip strengthening, or individualized cueing during sprint training.
Single-Leg Hamstring Bridge or Repetition Endurance Tests
Another identified injury risk factor is the hamstring’s level of tolerance to fatigue. Time or repetition-based tests which assess endurance and posterior chain control, such as single-leg bridge holds or repetitions to fatigue, can identify endurance deficits in posterior chain muscles, which may predict susceptibility to fatigue-related hamstring strains.
Surface Electromyography (sEMG) & Neuromuscular Activation Assessment
Neuromuscular control can also influence hamstring injury, which makes assessment of neural activity and muscle recruitment patterns a valuable screening tool. Measurement of muscle activation patterns and timing during sprint or strength tasks can detect delayed or reduced hamstring activation, abnormal co-contraction with quadriceps, or inter-limb activation asymmetry. The data from these assessments will enable practitioners to integrate exercises which improve neuromuscular control into an athlete’s injury reduction program.
Subjective Athlete Feedback
Some of the most important screening data comes from the players themselves. Standardized measures of muscle soreness and wellness metrics, such as RPE, sleep, and fatigue, particularly with athletes who have a history of hamstring injury, flags players needing load reduction or targeted interventions.
Once practitioners have progressed through this comprehensive screening process, they will have identified not only those players categorized as having a higher potential for injury, but also the specific injury risk factors they are most vulnerable to. This data then empowers them to design and implement highly specific and individualized injury reduction protocols to each player in the squad.
Apollo is Critical to a Successful Injury Reduction Process
Apollo gives practitioners the tools to act on this information in real time. By centralizing injury histories, screening results, GPS load data, and wellness feedback in one platform, practitioners can quickly spot patterns, such as a hamstring strain risk in a player showing declining eccentric strength and elevated sprint load. Automated alerts and AI-driven insights mean practitioners can adjust training plans before an injury happens instead of reacting to muscle injuries after they occur. Apollo facilitates proactive, evidence-based reduction protocols, which is exactly why the clubs that adopt Apollo see significant reductions in time-loss injuries over a season.
To Be Continued…
In the concluding part of this series, we will discuss the final stage in the injury reduction framework – the application of injury reduction protocols.
To learn more about using Apollo for injury prevention, email info@apollov2.com.
Written by Adrian Lamb, Apollo Sports Scientist
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