Discussion
To guarantee the internal validity of the study, it was necessary to standardise data collection, to define the population of the same team that submitted to the same protocols of technical and medical committee, that were at same environment and were submitted to the same training load in both seasons. In addition, the groups in seasons were homogenous for age, weight, height, body composition and training level (all of the subjects participated of First Division of Brazilian’s Soccer Championship) and there was no significant difference between number of games and time of exposure to training.
Thus, difference between both years was only introduction of thermographic analysis with the orientation of a prevention protocol, starting from an altered thermal result.
An epidemiological study in 51 soccer teams, comprising 2299 players, registered 2908 muscle injuries. On average, during a season, a player sustained 0.6 muscle injuries and a squad of 25 players can thus expect about 15 muscle injuries.1
In the present study, in 2015, the total number of 11 muscle injuries documented in 14 players was higher than Ekstrand’s study, and, it represented that a player sustained 0.78 muscle injury. In 2016, the total number of muscle injuries decreased to 4 in 14 players and, it represented that a player sustained 0.28 muscle injury (reduction of 64% with p value analysis of 0.04).
Overall, 6867 hours of exposure (5376 hours of training and 1491 hours of match play) were registered in 2015. In 2016, 6762 hours of exposure (5376 hours of training and 1386 hours of match play) were registered. Thus, injury incidence was 1.6/1000 hour in 2015 and 0.5/1000 hour in 2016.
We found that muscle injuries were reduced in 2016. The only difference in athletes training routine, during 2 years (2015 and 2016), was thermographic analysis and intervention with a load reduction programme in cases where we identified an ‘abnormal’ signal. Although we cannot attribute cause to this association, we respectfully suggest that possibility need to be considered—that the studied method and the prevention protocol reduced injuries.
Considering the players who remained with the team for both seasons, we observed an important reduction in the incidence of injuries. Due to this small sample (seven athletes), there was no statistically significant reduction between both years (p=0.06). However, there was a large reduction (63%), which is very close to reduction in full group (64%).
Our findings extend existing literature4 as the greatest number of muscular injuries detected occurred during soccer games (93% of muscles injuries) than during training. In 2015 and 2016, 91% and 100%, respectively, of lesions occurred during matches.
Literature shows that 92% of muscle injuries affected the lower extremities. The hamstring (37%), adductor (23%), quadriceps (19%) and calf (13%) muscles were the most common injury locations. Injury to the hamstring muscle group was the most common single injury subtype, representing 12% of all injuries. The majority of quadriceps strains (60%) affected the dominant leg (preferred kicking leg), 33% affected the non-dominant leg and 7% affected both legs or the leg dominance was unknown (p<0.05). The dominance of muscle injuries to the kicking leg was less obvious in other muscle groups (hamstrings, 50%; adductors, 54% and calf muscles, 51%).1 The present study reported a result of 87% of injuries occurred in hamstring with a dominance of 53%, as literature showed.
A systematic review about injury incidences in soccer players showed six studies where the majority of injuries were considered moderate and four studies where the majority of injuries were mild.14 Although most players were able to return to full training and match play within 4 weeks, muscle injuries are a substantial problem for the players and their clubs. A team of 25 players at the elite level can expect about 15 muscle injuries each season, with approximately 2 weeks missed for each injury. This quantity of time loss could be devastating because players sidelined due to injury limit the possibility of optimal performance by the team.1 The present study revealed that majority of injuries were mild.
Several researches reported on recurrent injuries in soccer players. Prior muscle injury is commonly suggested as risk factor for soccer players. Reinjury incidences range between 9% and 30% in professional adult soccer players and cause longer absences than new injuries. Findings from this study show that athletes who had muscle injury in the first year (2015) did not present lesions at the same site the following year. Thus, the early identification of the risk of injury, through thermography and the preventive protocol applied, was important because there was no reinjury. Thus, the severity of lesions and time away in 2016 was lower.
As important as number of injuries is the time away of the athlete to treat the injury. The results showed that in 2015, players spent 189 days in Medical Department to treat muscle injuries. As early as 2016, the time taken for treatment was 62 days. Thus, in 2016, more players were available to play and train than there were in 2015.
Understanding the commercial value of an athlete in game conditions, it is important to consider the cost of an athlete in medical department. Considering that, mean salary of cast is U$75,000,00/month, cost of players absence as a result of muscle injuries was, in 2015, U$472,500,00, instead U$ 155,000,00, in 2016.