**1. Introduction**

Muscle injuries are frequent in sports, and represent about 30% of all time-loss injuries in men's professional football (soccer) [1-8] and almost 20% in men's amateur level [9].

Four muscle groups of the lower limbs account for 92% of muscle injuries (hamstrings 37%, adductors 23%, quadriceps 19%, and calf 13%) [1].

In sports such as soccer, but also in athletics, basketball, volleyball etc, muscle indirect injuries and overuse injuries are more common (about 96% in soccer [1]) than direct injuries (contu‐ sions). Contact situations are more frequently involved in muscle injuries in other sports like rugby, American football, ice hockey [10,11]. In elite soccer 16% of muscle injuries are reinjuries and cause 30% longer absence from competitions than first injury [1].

Muscle injuries result from a complex interaction of multiple risk factors and events.

Several parameters are usually identified as risk factors. These are usually classified as either intrinsic, athlete-related, or extrinsic, environmental risk factors.

Gender [1,12], age [2,13-21,45], skill level [12,23,24], body size and composition [14,25,26], previous injury history [2,3,8,13,15,16,19,21,27,28,43-45], anatomy or biomechanics abnormal‐ ity [19], joints ROM and flexibility [29,30], muscle strength, imbalance and tightness [2,21,22,29], limb dominance [14], training errors such as poor technique, or errors in training program, warm-up or cooling down [33-35], aerobic fitness [25], fatigue [16,26,32,45], are included among intrinsic risk factors. Footwear, climatic conditions and turf type [36-42] are examples of extrinsic risk factors. Some of these risk factors can be modified.

Muscle injury prevention is advocated both by athletes and coaches. Yet, most of techniques for muscle injury prevention used by athletes or taught by coaches are entirely based on their own experience, but without supporting scientific evidence.

The aim of this chapter is to present current concepts about the prevention of the muscular injuries and to test which strategies are best supported by scientific evidence, both with respect to primary prevention (prevention of the first injury) and secondary prevention (re-injury prevention).

In this chapter are also proposed some practical suggestions, dedicated to the members of soccer's team, that are involved in the management of muscle injuries risk factors (coaches, fitness trainers, physiotherapists, team doctors).

When muscle injuries occur, the safe return to competition is often difficult, both in order to get prior level of performance and to avoid re-injury.

The anatomical healing of a muscle injury is a primary condition for safe return to sport, but it is not enough to manage re-injury risk. Thus, anatomical healing is not synonymous of "athletic healing".

A database of aerobic fitness, muscle strength, and other performance related parameters, is also proposed in this paper, to get a reference for the muscle injury rehabilitation program and the full return to competition.

**Figure 1.** Female soccer is today very popular.

mass and strength [21].

muscle injuries [12,22,23].

Age is a widely studied risk factor for muscle injuries, particularly in recent years, with the increase in the average age of players, especially at the amateur level (Figure 2). In available literature, there are conflicting data about age as a predisposing factor to muscle injuries. Some studies have identified increasing age as an independent risk factor for muscle injuries in Australian footballers [14-16] and soccer players [2,45]. These authors found increased risk in Australian footballers and soccer players older than 23 years [14,45]. Furthermore each year of age has been reported to increase the risk of muscle injuries by as much as 1.3 times in Australian footballers [15] and by 1.8 times in soccer players [17]. In a study on 123 female soccer players (age range 14–39 years), the authors found a significantly increased risk of overall injury in athletes older than 25 years compared with younger athletes [18]. In a study on professional soccer players the incidence of global muscle injuries increases with age, but an increased incidence with age has been found for calf muscle injuries only, and not for hamstring, quadriceps or hip/groin injuries [19]. During training sessions, players in the oldest age group (over 30 years) had a significantly higher incidence than young (below 22 years) players, while there were no differences compared to the intermediate (22-30 years) age group. During matches, young players had a lower incidence than the intermediate and older age groups [19]. All studies that report age as significant risk factor conclude that age increases

Prevention of Muscle Injuries — The Soccer Model

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hamstring injury risk independently of other variables such as previous injury.

nerve root due to hypertrophy of the lumbo-sacral ligament [22].

The explanation for increased muscle injury risk, with age is quite controversial. Some authors maintain that it is due to an increase of weight and a reduction of the flexibility of the hip flexors in athletes 25 years or older [20]; others indicate the cause in the reduction of lean body

Other hypotheses are age-related changes in muscle structure [13] and entrapment of L5/S1

However, there are also some studies that found no correlation between aging and increase of

**• Age**

These parameters have to be registered by laboratory and field tests, performed by the healthy athlete, during pre-season and competition period and then, in case of muscle injury, these have to be used as a reference, to programme his return to prior level of competition.

In relation to the authors' personal experience, this chapter will be set on the prevention of muscles injuries in a male professional soccer team: the suggestions and observations here described are, however, applicable to lower levels soccer teams and most others sports.
