Our expert EFP-Group agreed that their most effectively perceived exercise-based strategies to prevent muscle injury were (see Table 1); sprinting and HSR (very effective +++), eccentric (effective ++) with horizontal and vertical plyometrics, dynamic and static flexibility, core stability, concentric and isometric rated as somewhat effective (+). Consensus was not reached on precise effectiveness of some other exercise modes; multi-joint exercises (e.g. squats, Olympic style lifts etc), single-leg strength and stability and agility were rated between somewhat effective to very effective while kicking and resisted sprints ranging between not effective through to very effective. The day to perform specific sprinting and HSR or eccentric exercises depended on the proximity of previous and upcoming matches. While the first round of our Delphi survey highlighted a number of exercise strategies as at least being somewhat effective and others with an unagreed level of perceived effectiveness, the scope of covering all exercise types (i.e. 15 exercise types were highlighted in Round 1, with 10 agreed on for their perceived level of effectiveness), both in ensuing rounds of the Delphi and in this paper are too great. As such, we focused our efforts on obtaining deeper information on the two most importantly perceived exercise types; sprinting and HSR in addition to eccentric. We would like to make it clear to the reader from the outset, that by doing so we are not negating the potential role of the others nor are we confirming that the choices of the steering committee are necessarily the correct choice. The objective of the Delphi survey is to present the perspectives and agreements of practitioners working in the “field” irrespective of their real efficacy. The Delphi experts also requested (and later found consensus on) highlighting that exercise-based strategies must be accompanied by other non-exercise-based strategies if preventive strategies are to be optimised. These were; management of training week (+++), consideration of the previous injury, ability to work together, team communication and recovery strategies (all ++).
Sprinting and HSR
While sprinting and HSR has traditionally been viewed as a ‘problem’ (i.e. injury mechanism), there is now emerging opinion to suggest that when integrated into a well-planned programme, it may actually provide a ‘solution’  i.e. preventive effect. Our finding lends some subjective support to this notion. Given the most common muscle injury in elite football is the hamstring injury [21, 22], combined with reports that the majority occur during sprinting and HSR [23, 24], it seems appropriate to suggest that sprinting and HSR has a pivotal role, though the precise role as a protective factor still needs to be confirmed and if so, then clearly defined. It is important to highlight, that high-quality scientific evidence regarding any role of sprinting and HSR in muscle injury prevention is still lacking in male elite football and currently this supposition is based only on opinion  (including the current Delphi survey). Accordingly, we strongly recommend these suggestions be an urgent priority to validate (or refute) by researchers working in the area of male elite football.
EFP-Group Agreement #1: Individualise Sprinting and HSR Based Relative to the Players’ Own Maximum Speed
It was agreed that prescription/monitoring of sprinting and HSR should be based on individuals’ maximum speeds and not on absolute thresholds as commonly defined in previous literature and often used as factory settings on GPS. This follows logic, that when using individual speed thresholds, slower players perform greater amounts of high and very high-speed running compared to faster players who perform less when compared with absolute thresholds . We recommend a distinction between sprinting and HSR. Although limited evidence exists, it may be necessary to achieve maximal or near-maximal speeds, as high-speeds alone might not be sufficient to protect against injury [27,28,29]. However, since there are few studies examining the effect of sprint speed/exposure on injury in elite footballers, future investigations are required.
EFP-Group Agreement #2: Integrate Sprinting and HSR into Coaches’ Training Drills
Wherever possible and appropriate, it was agreed that sprinting and HSR exercise should be integrated into coaches normal training drills. This will likely have important implications to gain coach buy-in and enhance player motivation to perform such maximal natured actions with quality. It may also provide greater specificity of muscle actions that cannot be targeted during generic sprinting drills (e.g. sprinting and kicking ball at full speed) and concomitant decision-making. Despite a preference to incorporate sprinting and HSR into the technical/tactical drills designed by the coach, the experts agreed that it is appropriate to implement specifically designed football drills and generic running (e.g. maximal aerobic speed, repeated sprinting etc.) to ensure players are exposed to sufficient amounts of these activities. This may be particularly important to ensure maximal and near-maximal speeds are achieved as incorporating during drills such as small-sided games may not allow players to reach such speeds. It is beyond the scope of this article to go into great detail on designing individual, position-specific drills, however, we do provide some insight into the overall principles and direct the reader to some potentially useful guides by Bradley et al. , Buchheit [31, 32] and the FC Barcelona Muscle Injury Guide  for further insights and specific recommendations into practical programming. It is important to note that these are guides only and any effectiveness has not been scientifically validated, however, overall it is suggested that replicating running profiles of players is not sufficient and the types of runs must be considered also. For example, Bradley et al.  recommend an integrated approach based on match analysis using types of runs while your team is in possession (e.g. drive inside, run behind/the channel, overlap, break into box, push up pitch) and out of possession (e.g. close down, cover, recovery run, ball over top/down side). Buchheit [31, 32] showed how HSR can be programmed in real-life scenarios to maintain a stable week-to-week HSR load for substitutes especially (24), and how the optimal HSR dosage can be prescribed in relation to (1) the HSR demands of other tactical/technical contents and matches and (2) the different weekly microcycles length (i.e., number of days between games). The FC Barcelona Guide  highlights approaching training drills to target alongside the player integration of player and position-specific technical tasks (1) neuromuscular components as well as (2) metabolic conditioning, where neuromuscular training refers to accelerations, decelerations and changes of direction and metabolic conditioning referring to the contribution and development of the aerobic and/or anaerobic energy systems. Care may need to be taken when implementing maximal efforts into training drills as inappropriate inclusion could feasibly also increase the risk of injury.
EFP-Group Agreement #3: Players Should Accumulate 100% of Their Worst-Case Match Sprinting and HSR Over the Training Week, But We Aren’t Sure How to Define That
During periods with one match per week (≥ 5 days), it was agreed that the ideal GPS-based target for sprinting and HSR is 100% of individual players worst-case match scenario i.e. what the players maximum demands for these metrics. Viewing worst-case scenario as a global figure from a match (as was the case in this Delphi) raises some conceptual concerns (which were beyond the scope of both our Delphi survey and this article), however, it is important to acknowledge. We still do not know exactly what the worst-case scenario is in terms of volume or intensity or both, nor how it is distributed across a match. For example, a target of 200 m of sprint distance from a match may be the highest distance sprinted by a player, but how is this actually accumulated over the course of a match? For example, that 200 m in the match could (theoretical example only) be composed of 10 × 20 m efforts, so would training with 4 × 50 m efforts be appropriate to match the specific demands. Additionally, are the sprinting efforts linear or curved for instance. These are crude examples, but just to highlight that a global WCS from motion analysis data likely does not provide the full picture. Furthermore, one or two isolated GPS metrics (as highlighted here) does not consider other important football actions such as change of direction, dribbling, jumping, passing and shooting nor does GPS give an indication of internal psychophysiological load. Preparing players to perform a global worst-case scenario is not the same as preparing them to sustain repeated phases of high-intensity activities, nor coping with such activities towards the end of matches when players may be fatigued both physically and mentally. Future work is urgently needed to determine what a ‘worst-case scenario’ actually is (and how it can be defined and quantified, and even if such a phenomenon exists) for both internal and external load measures and how these can be appropriately trained.
During ≥ 5 days between matches, it was agreed that sprinting and HSR focused exercise be performed on M − 3 (i.e. 72 h prior to next match) which falls on either M + 3 or M + 4, depending on whether it corresponds to a 5 or 6 day between-match cycle. Importantly, when there are ≤ 4 days between matches, it was agreed that no specific sprinting and HSR exercise be prescribed to starters, as targets are probably attained during matches. However, substitutes should be prescribed additional sprinting and HSR exercise on Matchday + 1 (M + 1) or M + 2, (depending on scheduled rest day) but not on both days. Indeed, it has been proposed that match-play is an important stimulus (in particular neuromuscular load) to ensure players are prepared for match-play and this is necessary to replicate in substitute/non-playing squad players .
Eccentric exercise was perceived as an ‘effective’ (++) exercise strategy for muscle injury prevention. This is consistent with perceptions of other elite football practitioners from premier league  European Champions League  and the 2014 FIFA World Cup . Eccentric exercise may be particularly useful as it targets various potential and (importantly) modifiable risk factors for muscle injury  including, eccentric strength, optimal angle of peak torque, and muscle architecture e.g. fascicle length. It, therefore, appears that practitioners are attempting to follow evidence-based guidelines in their practice. Even if the scientific evidence in elite male players is not clear due to various sources of bias as highlighted previously, it is not typically the role of the sport scientist in a team to analyse the risk of bias in a study. Researchers should focus carefully on the design, implementation and reporting of high-quality, low-risk of bias studies.
EFP-Group Agreement #4: Integrating Eccentric Exercise into the Football Training Week
To our knowledge, there is no scientific evidence with regard to the optimal day/s to implement eccentric exercise in the elite football training week. According to the EFP-Group, during periods with ≥ 5 days between matches, 3 days post-match (M + 3) is the preferred day to perform the main eccentric exercise session of the week. Importantly, however, if we consider a week with 5 days recovery, M + 3 also represents the M − 3, which, in the same cycle, is the preferred day to perform sprinting and HSR exercise. When asked if it is appropriate to perform both sprinting and HSR in addition to eccentric exercise around the same session, there was no agreement. The responses revealed that this could be appropriate, but is highly contextual and depends on the planned sprinting and HSR session, and the decision should be based around this. One respondent proposed a double session (i.e. morning and afternoon) may remedy this problem. Another respondent also highlighted that eccentric exercise performed the day before a main sprinting and HSR session should consider the content of that session before implementing eccentric exercise. Overall, it appears that the context and content of preceding and upcoming sessions as described above is critical when planning preventive exercises.
During periods with ≤ 4 days between matches, it was agreed that low-intensity eccentric exercises (defined as ‘low-load, low volume) can be used. To our knowledge, there is no scientific evidence for low-intensity eccentric exercises to prevent muscle injury in elite footballers. A common theme in the written responses was that players should be accustomed to performing the eccentric exercise to allow these during congested periods.
While not in elite players, one study in semi-elite has investigated the scheduling of injury prevention exercise . When eccentric exercise was performed on M + 3 (as was agreed in our Delphi) both residual fatigue (perceived muscle soreness) and muscle damage markers (creatine kinase) were present on M − 1. Importantly, however, muscle function measured by isometric muscle contraction (muscle function is considered the gold standard for assessing muscle damage and persists with the muscle until fully recovered)  was unaffected by scheduling eccentric exercise on M + 3 in a 6 day match cycle. Interestingly, the same study demonstrated that performing eccentric exercises on M + 1 was tolerated by players and resulted in no residual fatigue or muscle damage markers evident on the M − 1. This could be particularly important during periods ≤ 4 days between matches to maintain any detraining of muscles . However, these are speculations and need to be thoroughly investigated to make confident programming decisions with male elite footballers.
EFP-Group Agreement #5: Eccentric Exercise can be Performed Either Before or After Football Training
A key question in the design of the eccentric exercise prevention programme is when to perform the exercises i.e. before or after training? It was agreed in our Delphi survey that it can be appropriate to perform either before or after football training. While lacking scientific evidence, preliminary studies reveal that there may be different adaptations for before or after. Performing eccentric exercise before training has resulted in fascicle length increases (short fascicle length proposed as an injury risk factor ) but not when performed after the session . Similar chronic adaptation of peak torque production of the hamstring muscles has been shown to be similar when eccentric exercise is performed before and after the training session . Conversely, when eccentric exercise is performed after the session increases in muscle thickness and pennation angle have been observed . Additionally, chronic adaptation towards an improved ability of players to maintain their eccentric strength at half-time and upon cessation of a simulated football match have been found versus those performing in a fresh state before training . Again, it is important to comment that the responses we received highlight that knowledge and consideration of the preceding session/s and upcoming session/s are important when deciding when is most appropriate to schedule the eccentric session. One response from an EFP-Group expert was to prioritise ‘safety’ rather than a specific adaptation i.e. to perform the eccentric training after so that players have full strength when going into the training session. Again, this represents an expert opinion and we need high-quality research to provide higher evidence-based recommendations.
No Agreement on Programming Variables
We did not reach an agreement regarding specific programming variables of eccentric exercise, i.e. optimal number of exercises, sets and repetitions, nor an appropriate range. Therefore, even if a specific range is defined in the scientific literature e.g. to maximise strength or hypertrophy, it appears evidence-based recommendations would be difficult to fully apply in the practical setting and will depend on a given context within the football team. “Appendix” provides the individual responses of the EFP-Group and highlights the variability in responses.