As mentioned before, most of the muscle injuries in football are muscle strains due to an indirect mechanism.

This kind of injury happens usually on the myotendinous junction where the muscle fibers converge and the forces tend to be more tangential in this place, turning it more prone to injury during eccentric efforts when the connective tissue is heavily tensioned. Besides that, the myotendinous junction is also a less irrigated tissue, which may contribute also to the injury risk at this location. However, muscle strains may also occur in myofascial location or, less often, being an intramuscular injury [5].

Although the typical injury mechanism of each of the most frequently injured muscles in football is different (e.g., groin muscle group while changing direction), it usually happens during an eccentric effort, when the muscle is elongating at the same time it is contracting (e.g., hamstrings slowing down the thigh and leg while sprinting) or in the transition between the eccentric and concentric phase of the movement [6].

Table 32.1 represents the most frequently injury mechanism for each muscle group in football.

According to Ekstrand et al. [1, 2] studies, in general, a professional football team can expect around 58% of the muscle injuries will result in an absence of more than 1 week, whereas 11% of the muscle injuries will be able to be classified as severe once it will cause a period of training and match absence of more than 4 weeks.

Quadriceps strains were the injuries that caused longer absence periods of around 17 days on average, followed by calf muscles (15 days), hamstrings (14 days), and groin strains (13 days).

Besides not being statistically different between them, quadriceps and groin muscle group are the ones with higher recurrence rate (17%), followed by hamstrings (16%) and calf (13%), leading to higher absence periods than the index injury [1, 2].

Nowadays, the term “injury prevention” is one of the most mentioned in sports environment. Injuries may lead to decreased competitive performance, reducing players’ availability to train and play. That is the reason why epidemiology and risk factors identification have a considerable importance once it will give us the lead to decrease injury risk.

There are two kinds of risk factors, non-modifiable and modifiable. The first ones are related with race, age, or weather, for instance, those are the ones that, besides being important, sports professionals are not able to interfere on it.

On the other hand, modifiable risk factors identification has a significant importance to sports professionals once, addressing them, professionals might be able to decrease injury risk – strength, range of motion, and motor control are examples of this category.

Longitudinal studies have been helping sports community to better understand muscle injuries’ risk factors in football; however, there is still some conflict in literature when trying to quantify the strength of each risk factor identified [7].

Considering the continuously high recurrence of muscle injuries besides all the efforts made in order to prevent it, sports professionals should consider that not all risk factors are identified still, a fact that can be leading us to an ineffective approach regarding the modifiable risk factors [8].

Figure 32.2 represents a hierarchy relative to the existing level of evidence regarding each muscle injury risk factor [7, 9–15]. On the bottom of the pyramid are seen two levels of muscle injury risk factors that have a significant amount of evidence to be considered as a risk factor for the most relevant football muscle injuries, followed by the intermediate level which represents risk factors that are important and gather a considerable amount of evidence in some of the more common football muscle injuries; and, on the top of the pyramid are represented the muscle injuries’ risk factors that, besides being clinically significant for sports professionals, there is still some controversy regarding its strength as a muscle injury risk factor taking in consideration the small amount of and ambiguous studies outcomes.

Considering the importance of muscular strength as a risk factor in hamstring injuries, the normalization of eccentric strength and functional ratios between/in both sides are of significantly importance when trying to prevent its strain [16]. However, muscle injuries are multifactorial, with modifiable/non-modifiable risk factors and some others that might be still unknown – considering the consistent significant incidence and recurrence of muscle injuries in football throughout the years – which means that, regardless all the efforts, prevention strategies are tools that might allow us to decrease the injury risk, but will not assure that injuries will not happen [8].

Muscle injuries’ risk factors assessment should be done during the preseason screening and monitored systematically during the season (see Chap. 34 in this book), in order to:

Figure 32.2 shows the injury risk factors that should be assessed and controlled during the season in order to establish athlete’s muscle injury risk profile, being able to develop an individualized injury prevention program addressing those risk factors.

Muscle injury prevention programs’ aim is to decrease/eliminate or manage the know injury risk factors of each athlete, focusing especially on the modifiable ones. However, some non-modifiable risk factors might be addressed indirectly. Considering “age” as a risk factor for hamstring muscle strains, besides not being able to modify it, but knowing that hamstring strains usually happen while performing a high-speed run or a sprint [4], sports professionals can control player’s very high intensity (VHI) distance during trainings, in order to decrease its risk of injury due to its intrinsic factor “age” that cannot be modified, avoiding an overload. This example highlights the importance of training load monitoring and also the need to create cutoffs on players’ training load goals considering their injury risk factors and athlete’s individual fitness performance profile.