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EPL Illustration: Eamonn Dalton / The Athletic; Getty Images Change is the only constant in football. In the modern game, players can reasonably expect to meet new team-mates, new managers (or head coaches), and fulfil new tactical demands within an average two-year cycle. Combine that with an ever-congested fixture calendar, and it can be difficult to keep up with the physical requirements that are placed on a professional footballer. Advertisement The frequent upheaval means that adaptability has never been so important. However, with body profiles that are so finely tuned at the elite level, there is an elevated risk of injury among players when adjusting to such changes. Research has highlighted that the volume of matches might not be the primary factor affecting player welfare, but rather the increased physical intensity of the modern game — particularly in the Premier League. There is nuance to this topic, so can we add another layer of context? Some injuries can occur without warning (i. e. those involving bodily contact with an opponent), but there are certain pinchpoints within a season that can heighten the prospect of a player needing to spend time on the treatment table. The incidence of muscular problems has been rising for many seasons, but their association with an increasingly high turnover of coaching staff is less discussed. Analysing 65 leagues worldwide, a 2025 report from the CIES Football Observatory highlighted that 66 per cent of managers were in their position for less than a year. In the Premier League, two-thirds of them were in charge for less than two years, with an average tenure of 777 days across the 20 clubs. A fresh face in charge will invariably bring a new approach with them. Adapting to these revised tactical demands is one thing, but an incoming manager will often arrive with their own coaching and medical staff in tow. The subsequent change in physical conditioning — whether it is underloading or overloading players’ output — comes with its own risks for injury across the squad. A 2025 study explored trends across an eight-season period for a team in Croatia’s top division, with total (contact and non-contact) injuries increasing by 35 per cent within four weeks of a new manager’s arrival. Advertisement These findings build on a 2023 research paper that analysed 14 European teams across three seasons to monitor squad injuries, with a close relationship found between changes in a manager/head coach and the risk of players picking up hamstring problems. This effect was most pronounced when the arriving boss added a new fitness coach or team doctor to their support staff. “Something as simple as changing training pitches or training schedule can have massive consequences, ” says Callum Walsh, who is now assistant coach at leading Portuguese side Porto, having held roles at Ajax in the Netherlands, Turkey’s Alanyaspor, and Newcastle United and Huddersfield Town in England. “For a typical Saturday matchday, some managers will do a more European model — i. e. Thursday off the grass. Some will use a German model or tactical periodisation — i. e. Sunday or Monday off the grass, and four-day lead-ins. “In the traditional English model, you might be off on Wednesday. It doesn’t sound that different, but for players with a certain injury history, they might do best with certain days off the grass — if not, you could break them. If you’re going to change the manager, there’s a strong likelihood that changing your training week might come with an injury spike. ” A new manager often arrives at a time when the team concerned are underperforming, meaning they are compelled to get positive results quickly after coming through the door. Six managerial changes have already been made in the Premier League this season — two of them at Nottingham Forest. The Forest players would be forgiven for needing time to adapt to the stark stylistic switching from Nuno Espirito Santo to Ange Postecoglou to Sean Dyche in less than two months but the latter, the club’s current head coach, was quick to comment on the physical condition of the squad he inherited. “I am not knocking any other manager, but I have been in the Premier League for 11 years and I know where I want my team to be physically, ” the former Burnley and Everton boss told Sky Sports in October after a 2-0 loss to Bournemouth in his first league game in charge. “I don’t think the players are where they need to be for my way of working. ” Change can be for the better, but it is a fine balance in managing squad workload to ensure that each player still has the requisite fitness to execute the new demands placed on them. Advertisement Previous research has discussed the “training-injury prevention paradox” that suggests higher training workload can result in fewer injuries, but the specific match conditions can be difficult to replicate in football. Asking players to fulfil the physical demands of an 11-v-11 game in every training session is an unrealistic and dangerous expectation to place on them. “Some managers coming in will probably tend to be a little bit more risky because of the (league) position that they have been hired in, ” Walsh says. “They’ve got a decision to make in terms of fitness, but also tactically — (sitting through) more meetings can be cognitively fatiguing. “If you look at American college athletes during exam periods, you will often see an injury spike. When you’re cognitively overloaded, there are chemical releases that impact power output and biomechanics — so risk of injury actually goes up, even if you’re not on the training pitch but doing four hours of meetings every day. “So you could work your new squad really hard mentally and have longer tactical sessions on the grass to make sure you’re right physically — but that comes with a risk of injuring players. Alternatively, you could spread the workload out over six or seven weeks, but if you don’t win (in) your first four games, then questions will be asked of the impact you are having. ” A manager’s arrival can often come with a change of system that might require certain players to take on roles different to those they were previously accustomed to. Midfielders might be asked to play in the full-back positions — or vice versa — while wingers might be asked to work as a wing-back in a back-five system. Unique movements associated with such specialised positions rely on specific muscle groups to fulfil the physical demands. For example, a striker will be engaging their hamstrings when making short, sharp sprints during straight-line movements, while a defensive midfielder is more likely to engage their groin muscles when making lateral movements across the width of the pitch. Of course, some players are more adaptable than others. Advertisement For those wondering, Sunderland’s Dutch international defender Lutsharel Geertruida is the most versatile player in the 2025-26 Premier League by The Athletic’s measure, filling eight positions in his debut season in English football for coach Regis Le Bris — most notably centre-back, full-back and defensive midfield. Crucially, changing position introduces different physical and biomechanical stresses to a player’s body. These can be primary, such as a hamstring injury resulting directly from altered physical demands, or secondary, where different tactical requirements lead to uncertain movement, reduced peripheral vision that can increase the likelihood of contact injuries or fatigue-driven compensatory ones in other areas. “We had a player at Huddersfield, and he was a machine in central midfield — sprints all day long, ” Walsh says. “Occasionally, he had to play left-back and every time he did, he pulled his calf, because all of a sudden, he’s having to backpedal. “In general, players can get more fatigued (when switching roles) because the (new) position is less subconscious, and it is probably more taxing for them. It might just be a split second, but the rhythm of the game is so different in different areas of the pitch — so you might be more likely to get caught on the heel or ankle if you do not evade a tackle in the same way. ” A positive example of a role change improving player availability is Chelsea captain Reece James. This season, James has been on the pitch for 73 per cent of the available Premier League minutes, which is the highest share of playing time in a senior Chelsea career that began in 2019. As The Athletic has previously analysed, it is no coincidence that James’ improved health has come at a time when he has been playing not in his prior role of full-back but as a defensive midfielder, which requires fewer of the high-intensity runs that come with greater risk of muscle injury. Advertisement These positional differences in physical requirements can be seen using data from Skill Corner, comparing the volume of high-speed runs (at a speed between 20 and 25 km/h) per game across different playing roles in the Premier League. As shown below, a wing-back position requires the most high-intensity runs on average, with wide players typically taking on a greater sprinting load than those playing in the centre of the pitch — i. e. centre-backs or defensive midfielders. While centre-backs show the lowest high-intensity running relative to other players, a 2023 study showed a notable rise in sprint distance for them across a five-season period — showing how the influence of tactical trends (e. g. a higher defensive line) impacts the physical demands placed on certain positions. Sudden changes in tactical approach can highlight this injury risk among centre-backs. Nottingham Forest’s switch from Nuno to Postecoglou saw them shift from a manager with the second-deepest defensive line (22. 6 metres) to the second-highest (33 metres, Tottenham Hotspur) in the previous season. Had Postecoglou stayed longer, you would suspect that his defence would have had similar muscular issues to those seen during his time at Spurs. The Premier League trend largely holds across the other four leagues in Europe’s top five, but the interaction between positional and league-wide demands uncovers an extra layer of nuance in injury risk. For example, an attacking midfielder (labelled ‘AM’ in the graphic below) moving from Spain’s La Liga to the Premier League would be expected to make approximately 10 more high-intensity runs on average per game (51. 9 to 62. 5). That might not sound like a lot, but across the course of a full season, it can put significant strain on a new signing. These numbers help to explain why managers will ask for patience when new players are transitioning to new leagues, with the physical intensity of the Premier League known to be among the highest compared with its equivalents in continental Europe. It is a topic that has been at the forefront of Liverpool head coach Arne Slot’s press conferences this season, when he gets asked why his new-look side have dropped off from 2024-25’s title-winning form. Advertisement “The biggest adaptation if you come from abroad is this league and how intense it is, ” Slot told reporters at the start of this month. “I think even when we play once a week, you could see that Hugo (Ekitike, one of Liverpool’s summer signings) had cramp after 70 or 75 minutes (against Wolves) — and I didn’t take Florian (Wirtz, another player in his first English season) out because he played badly, I took him out because he was hardly able to keep on running anymore. ” Unsurprisingly, both Ekitike and Wirtz have endured muscular strains this season as they adapt to Slot’s tactical style and the demands of the Premier League. While his move last summer was from one Premier League club (Newcastle United) to another, Alexander Isak’s lack of pre-season was also a contentious issue, with Liverpool fans calling for their record signing to be given more playing time earlier in the campaign. Slot was keen to manage Isak’s minutes carefully, with eyebrows raised after the 26-year-old was made to do extra running at half-time immediately after being substituted in the Carabao Cup tie against Southampton in late September. While it was queried by some at the time, there was method to the perceived madness. “If you play him for 45 minutes, then top him up with straight-line running, the injury risk is astronomically less (than playing him in the game for longer), ” Walsh says. “You can build that tolerance more carefully — so Isak probably would have ended up doing the equivalent high-speed and sprint distance as if he had played 75 to 80 minutes. “This way, you can manage the fatigue and chaotic factors by doing box-to-box, stride-outs and sprints. There is no right or wrong method, but it is less risky — which is not easy when you have spent £125million on a striker and everyone wants to see him play. ” While data-informed decision-making has increased in recent years, there is no perfect science when managing a squad’s workload. Greater change can often lead to a higher likelihood of player injury, but the key decision is often placed in the hands of the coaching staff. So it all depends on their assessment of risk. Mark Carey is a Data Analyst for The Athletic. With his background in research and analytics, he will look to provide data-driven insight across the football world. Follow Mark on Twitter @Mark Carey93