“How much exposure is too much exposure”—an investigation into the importance of sprinting at high velocities to limit injury risk.

Hamstring injuries remain and are consistently one of the highest occurring soft tissue injuries in field sports, particularly those that consist of high speed running and transitions such as football, Gaelic games, Rugby and track events (Ekstrand et al., 2016). In recent times research has proven time and time again that hitting your max speed is the greatest vaccine you can take to reduce your risk of hamstring injuries whilst also improving your max speed. It is now widely researched and proven that the exposure to high speed running helps and promotes positive adaptations in the neuromuscular system to add and aid structural robustness in the muscle tissue needed to tolerate match day demands (Malone et al., 2017). Even with all this literature a crucial question remains how much exposure is too much?

Whilst we know insufficient sprinting increases injury risk particularly in hamstrings as the muscle tissue has not be adequately loaded to handle the volatile nature of the sprints (Kalema et al., 2022). In tandem, poorly or overly prescribed sprinting volume can also be equally hazardous. This blog aims to identify the current understanding of sprint exposure in injury prevention and the importance of identifying the need to clearly define the dose required to optimize performance and to reduce the risk of hamstring injuries.

Sprinting has been continuously shown to positively promote healthy hamstring function by simulating and replicating the demands placed on the tissue during match play demands such as acceleration, deceleration and max speed exposures (Opar et al., 2012). Numerous research studies has shown and proved that sprinting within the bandwidth of 90-95% of an athletes max speed sets off a series of neuromuscular adaptations that are beneficial and crucial to hamstring injury prevention such as increased biceps femoris fascicle length and greater levels of eccentric strength and force (Timmins et al., 2016). Similarly Malone et al showed that professional soccer players who had a greater level of weekly sprinting exposure within the bandwidth of 85%-90% had a significantly reduced risk of hamstring injury compared to those who had lower or no exposures within this bandwidth. This can also been seen to positively adapt muscle tendon units within the tissue, Bourne et al found that exposure to high speed and max efforts lead to a far greater level of resilience within the muscle tendon unit compared to athletes with lower levels of exposure.

These research findings collectively demonstrate that sprinting is not only beneficial or helpful but it is essential to keeping hamstrings and muscle tissue healthy for fast field sport games. It is clear sprinting creates a physiological insurance that protects them against soft tissue injuries.

Despite the clear and obvious benefits a growing amount of research warns that the mismanaging of sprinting volume, load and exposure can increase injury risk. Overexposure, particularly in athlete’s not conditioned or previously with low exposures to high speed running can lead to neuromuscular fatigue, poor and disrupted sprinting mechanics, tissue overuse and overland and ultimately injury inducing (Duhig et al., 2016). This injury risk is particularly prevalent when there is a spike in sprint volume and/or intensity as shown in the acute to chronic workload “ACWR” model which is a frequently used tool to monitor and prescribe progression and regression in running loads. Maintaining the acute to chronic workload between 0.8-1.3 has been deemed a sweet spot for loading (Gabbett, 2016), that being said this model has been under scrutiny for its limitations and lack of context in its application and its over simplified approach (Impellizzeri et al., 2020). However it still is able to identify excessive undulations in sprinting load which in turn can tip the scale from being a positive factor to an impeding one.

To explore sprint exposure fully we must firstly give context to what it actually is and how it occurs.

·      Sprint Volume (This is the total distance covered above a certain threshold e.g. 7m/s).

·      Sprint intensity (The athlete’s percentage of max speed e.g. 95%).

·      Frequency (how often you sprint weekly)

·      Recovery time given between efforts

·      Sprint type (max effort, submax effort)

·      Type of exposure (Game based, training based)

Most existing research defines these sprinting exposures between 85-90% however there is considerable variability in velocity thresholds and how different coaches define and describe high speed running vs sprinting. (Hunter et al., 2021). This lack of a standardised approach makes it considerably difficult to establish safe optimal and efficient guidelines.

Whilst it is quite evident that some sprint exposure is better than none there is little evidence of volume or the exact prescribed dose that account for the optimal prescribed dose. Malone at al noticed significantly lower injury rates when athletes were exposed 1-2 times greater than their 90% max in any given week, interestingly Duhig et al commented that 3 or more sprinting sessions per week without clearly defined progression or recovery can heighten and increase the injury risk. The exact dose in this instance remains uncertain. We know what is too little but do we truly understand what is too much?

The clear shape and structure of the dose and its response remains somewhat unclear and is often led to coaches operating off a number of justificatory circumstances. What we often see is a U shape or bell curve where too little is too risky and too much generates the same risk. The lack of individualised sprint tolerance indicators and poor inclusion of contextual factors into various different models creates a difficulty to pinpoint where the benefit of sprinting turns into direct risk. This is the inherent risk of any programming and always proves difficult when trying to program for a team sport in any sprinting context.

It is evident not all athletes respond the same to every exposures and stimulus they receive and that is no different to sprinting. Common factors such as their technique and sprinting mechanics, positional needs and demands, previous injury history, training age and neuromuscular and physiological make up all significantly affect how well an athlete will respond to the doses of sprinting they receive (Timmins et al., 2016).  A common factor associated with athletes who have a high injury risk from previous events are more susceptible to re-injury as a result in changes in sprinting volume, intensity, more often than not will require a gradual, prescribed ramp in sprinting metrics (Hickey et al., 2017).

The best way to monitor this controlled prescription is through the use of GPS data. This gps data is predominately used to monitor load, variance, and what type of metrics the athlete is hitting on a session to session basis. This in turn is used to help prescribe the future load an athlete will be exposed to. It is prudent of every coach to implement individualised targets into their programming for athlete’s as in a game every player will produce different metrics based off of their position, work rate, opposition and overall the type and style they are frequenting as a player.

Another key consideration is not just about how much we want our athletes to sprint and move through a high velocity but also when we program it within the micro cycle. Programming sprint work in windows where fatigue will be high such as within an intense training block, at the end of a highly fatiguing session can and will increase the risk of Injury (Shield and Bourne, 2018). So it is not always more is best, the timing and system in which we program is always important and it’s not as simple as throwing in sprint work and thinking as a coach, ‘that is that boxed ticked’. Careful and systematic periodization is to be of careful consideration as programming sprint for directly after heavy eccentric loading will increase neuromuscular fatigue and spike injury rates (Opar et al., 2012). Programming 48-72 hours post games or doing a period with low volume will always work best for speed as we want our athletes fresh when performing max speed work as much as possible.

Although it has been difficult to provide exact steps to follow as the research shows us they are several principles to adhere to in order to obtain optimal sprint dosage. It is prudent coaches build up gradual exposure over weeks rather than rapid increases. Coaches should individualize the dosage based of the athletes individual needs but hit a minimum of 1-2 sprints greater than 90% per calendar week (Malone et al., 2017). It is also extremely important that programming is made with the context in mind using an array of monitoring tools such as GPS and recovery scores whilst also communicating and listening to the athletes on a 1:1 basis understanding the importance of the fact all athletes have hugely differential needs.

Sprinting and high performance go hand in hand and it is the cornerstone of every team sport. The narrative of more sprinting is dangerous and it must change, evolve and more concise in depth and sophisticated models that take into account the entire context of the situation is needed. We need a refined approach, highly individualized, context driven with the athlete front and centre to transform the narrative from more sprinting the better to a precise injury prevention tool, where prescription is informed by precision and not generalisation.