Well. If you didn't know what hamstrings were by Christmas 2015, you sure do now. Liverpool have accumulated a preposterous 8 hamstring injuries in a month, with 4 of those coming in a 3-day span this week. Since the start of the season, the club has had 11 players suffer hamstring injuries, with several of those having more than one go-round. The average number of hamstring injuries for a 25-man squad over the course of a season is 6, so clearly, something is amiss.
Since the injuries started cropping up in December, fingers have been pointed every which way. Klopp's training is too intense! The players are running more! Not enough rotation! The holiday match programme! These millennial schoolgirls can't handle it like we did in my day (I'm guessing Tony Evans said something like this)! Footballers are in shitty condition (That's me)! As is usually the case, the problem is likely the result of a convergence of factors.
A muscle strain occurs when a muscle is stretched while it is being contracted. Too much of either, and the muscle fibers might tear. The hamstring is particularly susceptible to this - 40% of all football muscle injuries are hamstring strains - because it traverses both the hip and knee joint, creating unique demands on the muscle. During a sprint, as the hamstrings contract to pull the hip into extension, the foot being in contact with the ground causes the knee to extend, stretching the muscle from that end. This is a finely tuned balancing act, and the faster and more explosive the contraction is, the smaller the margins for error become. Injuries are typically seen early in matches, when the muscle is cold and unprepared for explosive work, or late, when it is fatigued and inter-and intramuscular coordination is reduced, leaving the muscle vulnerable.
A weaker muscle will always be more likely to get overloaded, as will a muscle that lacks the capacity to lengthen. Footballers are notoriously lazy with regards to their physical condition and ill-disciplined in the weight room, and while applying this to Liverpool's players is nothing more than educated speculation, what passes for stretching among Liverpool players indicates that mobility isn't exactly a strong suit either.
With fatigue such a big contributing factor to muscle injuries, it is unsurprising that they correlate so strongly with match frequency. Midweek matches have been shown to increase hamstring injury risk by nearly 30%, and this can be expected to rise when recovery time is shortened further. Muscular fatigue builds up over time, which means that players might not experience issues after a single mid-week match, but as the distance between physical demands and complete recovery grows, injury becomes more likely. Having a bigger squad and allowing some rotation, without completely interrupting the rhythm of the team, is an important asset for top clubs competing on many fronts.
In short, what we're seeing is a perfect storm of players that are missing crucial physical capacities, a lack of rotation over time, an extreme fixture congestion, and a new manager - whose stated goal back in October was to reduce the amount of injuries at the club - coming in with a new playing style that increases the demands of the players, seemingly without taking the other factors into account.
So how to fix this? Unfortunately, with things having gone this far, Liverpool are likely going to be forced to ride it out for now. The match programme is what it is, the number of players out with injuries rules out rotation, and any added strength training at this point will only contribute to increased fatigue. The club's best bet right now is likely to make sure the players who are injured don't come back prematurely, but receive the required recovery time and work needed, while making sure that the players who are carrying the load aren't overloaded between matches, focusing on tactical work and making sure tissue quality and pre-match physical preparation is of the best possible caliber.
The big changes need to take place when fixtures are further apart, with improved strength - can I get a Nordic Hamstring Curl amen? - and mobility at the very top of the list. A summer that sees both the Euros and the Copa America take place creates challenges, as players will come back from these competitions already fatigued, and the club has limited time to make relatively profound changes to the players' general physical condition. Communication with the international squads' support teams during the tournaments is going to be important, as will allowing players who return late the time needed to build up their capacity before playing full-intensity games. Fringe players who have spent the summer at Melwood and have gotten further in their training should be used generously throughout pre-season, and for as long as needed for the late-comers to get physically up to speed.
Should changes be made to the backroom staff? Possibly. Despite this season being particularly bad, it is not the first time in recent years Liverpool have struggled with injuries. A change of staff and philosophy may be needed. There have been whispers of approaching Oliver Bartlett, who trained Dortmund's players under Klopp's back-to-back league wins, and who has since overseen healthy high-intensity pressing teams in Red Bull Salzburg and Bayer Leverkusen. Whatever ends up happening, it is clear that in as competitive a division as the Premier League, with so many teams currently ahead of them in terms of talent and resources, Liverpool absolutely cannot afford another season at the top of the injury league if their ambitions are to be fulfilled.