Incorporation of a high-level soccer player into the team after a muscle injury: A case study

Fecha recepción: 01-05-14Fecha envío revisores: 02-05-14Fecha de aceptación: 03-06-14 Andrés Vargas Fuentes C/ Bulerías, 6 Bda.: El Sexmo 29570 Cártama, Málaga entrenamientodea@outlook.com Abstract: The aim of the study was to observe the evolution of the external load of a soccer player who just joined the team after a recovered injury.13 male football players of a soccer team (20.9 ± 1.7 years, 1.80 ± 0.05 m, 73.1 ± 5.3 kg) belonging to the 2nd division B participated in this study. After 30 days off following a hamstring injury a player started to train with the team. The next week his injury relapsed, so he had to stop training for another week. Finally he was re-incorporated to the team. External load was measured in the injured player (P) and the rest of the players of the team (T) using GPS devices (GPSport) during week 1 and week 2. The variables measured were: distance at high intensity (DHI; >14 km/h) and distance at sprint (S; >24 km/h). Besides, the number of times they entered the different acceleration rates: (Acc) 1 (0-2 m/s/s), Acc2 (2-3 m/s/s) and Acc3 (3-5 m/s/s) and the number of times they entered the different deceleration rates: (Dec) 1 (0-2 m/s/s), Dec2 (2-3 m/s/s) and Dec3 (3-5 m/s/s). During the first week of training, P performed longer DHI and S than T. Moreover, P performed higher acc1, acc2, acc3, dec1, dec2 and dec3 than T. In contrast, during the second week, T performed longer DHI and S than P. However, P performed higher acc1, acc2, acc3, and dec1 than T. However, similar values were found in dec2 and dec3 in P and T. It was observed that the acc and dec in both weeks indicated a higher peripheral muscle work in P. Therefore, according to the nature of the injury a modification or even avoidance of certain exercises should be considered especially those exercises that directly impact on the repaired muscles.


Introduction
Hamstring injuries are present in all soccer teams throughout the season.Recent studies have shown that 12-16% of all injuries in English and Australian professional soccer have been hamstring strain injuries (Connell et al., 2004).As result, soccer players were injured an average 18 days and could not compete in an average 3-3.5 matches due to hamstring injury (Orchard & Seward, 2002;Woods et al., 2004).Another feature of muscle strains is the recurrence rate, 34% of hamstring strains in the AFL being recurrences (Seward et al., 1993), making hamstring injuries one of the most common sources of injury and reinjury among footballers (Orchard et al., 1998).
However, there is a group of football players that shows an increased incidence of hamstring strains than any other.It has been found that there is a strong correlation between the optimum angle for the active peak torque and a previous history of injury (Brockett et al., 2004).It is thus that, previous injury has proved to be a relevant risk factor (Garrett, 1996;Upton et al., 1996).Into the bargain, hamstring strains were significantly associated with a low hamstring: quadriceps ratio of torque on the injured side hamstrings and low ratio side to side of the maximum torque (Orchard et al., 1997).However, others point out that hamstring strains are not related to a low hamstring: quadriceps strength ratio (Bennell et al., 1998).In brief, hamstring muscle strains are associated with eccentric contractions, where the contracting muscle is lengthened (Garrett, 1990;Kujala et al., 1997).Thereby many explanations have been proposed to explain the factors that cause the hamstring injury, such as muscle weakness and lack of flexibility (Burkett, 1970), fatigue (Garrett, 1996), insufficient warm-up (Worrell, 1994), and poor lumbar posture (Hennessy & Watson, 1993).
While hamstring strain injuries are common, our knowledge of the factors that predispose soccer players to injuries is scarce (Brockett et al., 2004;Verrall et al., 2001).One of the limitations of the studies is that the diagnosis of the lesions are carried out in the clinic, regardless of the factors present in the training field (Petersen & Hölmich, 2005).
To our knowledge, the training sessions of a soccer player after his recovery period (30 days off) from a hamstring strain injury has not yet been analyze.Therefore, the aim of the study was to observe the evolution of the external load of a soccer player who just joined the team after a recovered injury and to compare this load with the average load of the rest of the players.

Soccer Players
13 male football players, belonging to a national football second division participated in this study (20.9 ± 1.7 years, 1.80 ± 0.05 m, 73.1 ± 5.3 kg, 8.0 ± 0.9% fat percentage, VO 2 max During week 1 and 2 (Table 2), the inju red player performed higher acceleration 1, acceleration 2 and acceleration 3 than the res t of the team (week 1: 148 vs.  1: Average values (mean and standard dev iat ion) of the distance at high intensity (>14 km/h) and at sprint (>24km/h) of the i njured player and team.
Acc: acceleration Finally, the injured player performed high er number of deceleration 1, decel eration 2 and deceleration 3 than the rest of the team (113.75 vs. 8 0.94±15.51times, 41.50 vs. 31.45±8.31times and 14.75 vs. 11.41±4.00times, respectively) during the first week of training (Table 3).And during at week 2 (Table 3), the injured player performed higher number of Dec1 than the team (96.33 vs. 79.81±20.01times, respectively), and si milar values were found in the numb er of deceleration 2 and deceleration 3 in the injured player and the team (25.67 vs. 26.74±9.99times and 8 vs. 8.74±3.96ti mes, respectively).Injured player Team Injured player Team Injured player Team Dec3 (times) Dec2 (t imes) Dec1 (times) Table 3: Average values (mean and standard deviation) of the number of times in deceleration 1, deceleration 2 and deceleration 3 of the injured player and team.56.06 ± 2.68 ml/kg/min).All players had a wide football training experience (11.8 ± 1.7 years).Prior to involvement in the investigation, all participants gave written informed consent after a detailed written and oral explanation of the potential risks and benefits resulting from participation in this study, as outlined in the Declaration of Helsinki (2008).The participants had the option to voluntarily withdraw from the study at any time.Ethics Committee of the University of the Basque Country, UPV/EHU, approved the study.

Analysis, Validity and Reliability of GPS
The validity and reliability of GPS devices have been studied by several authors for application in football (Barbero-Álvarez et al., 2010;Coutts & Duffield, 2010;Portas et al., 2010;Varley et al., 2012;Vickery et al., 2013) as well as in others sports with high physical demands (Cunniffe et al., 2009;Lockie et al., 2013;Suárez-Arrones et al., 2013).In this way, the GPS devices seem to be reliable for the quantification of the physical load in both cases: matches and training session.
Testing took place across the centre of an open field, free from obstruction or adjacent buildings.All GPS units (GPSports, SPI-Pro, 15 Hz, Canberra, Australia) were simultaneously activated and left for 15 min.The GPS units (weight: 76 g, size: 48x20x87 mm; SPI Pro X; GPSports Systems, Canberra, Australia) sample at a rate of 15 Hz and are coupled with a 6 g triaxial accelerometer sampling at 100 Hz.The typical number of available satellite signals ranged between 9 and 11 accompanied by a mean horizontal dilution of position (HDOP) of 1.2 + 0.2 throughout the test period.A GPS vest (GPSports, Canberra, Australia) was tightly fitted to each participant, placing the receiver between the scapulae.Each of the GPS device was carried by a single player, for the registration of a period per period.It followed a pattern-player GPS to keep the same device during matches (Jennings et al., 2010).The data were downloaded through the appropriate software (Team AMS R2; GPSports) and processed data using Microsoft Excel program (© 2013 Microsoft).

Design
After 30 days off following a hamstring injury a player started to train with the team.The next week (week 1, Figure 1) his injury relapsed, so he had to stop training for another week.Finally he was re-incorporated to the team (week 2, Figure 1).External load was measured in the injured player (P) and the rest of the players of the team (T) using GPS devices during week 1 and week 2.

Statistical Analysis
The statistical analysis was performed using the data analysis program Statistical Package for Social Sciences -SPSS 20.0.1.(SPSS Inc., Chicago, IL, USA).Descriptive statistics for the analysis of all the variables studied was performed.Values were presented as mean and standard deviation (±SD).

Results
During the first week of training (Table 1), the injured player performed longer distances at high intensity and sprint than the mean of the rest of the team (799.85 vs. 687.97±126.73m and 45.50 vs. 41.72±31.03m, for the injured players and the rest of the team, respectively).In contrast, during the second week (Table 1), the team performed longer distances at high intensity and distances at sprint than injured player (651.57±211.04 vs. 598 m and 30.67±26.58 vs. 21.70 m, respectively).

Discussion
This study quantified the external load of a football player after having recovered from a hamstring injury and the subsequent relapse of the same injury.Data showed that the intensity of the training of the injured player was probably too high after a fairly long recovery period of one month, and this could be the reason for the relapse of his injury.In this respect, during the first week all the variables of the training load were higher in the newly incorporated player compared to the rest of the team; whereas during the second week, training intensity was reduced.However, accelerations and decelerations in both weeks indicated a higher peripheral muscle work in the injured player than team due to constant changes of direction in different tasks requested workout.
It has widely been studied the relation of the high intensity training with the rate of injuries during a season as well as the duration and load of training despite planning of different kind of exercises (Anderson et al., 2003).Notwithstanding, the effort made by soccer players during the first days of training with the team is still unknown.This would be important due to the fact that it has been observed that when an athlete returns to his or her first runs on the field, the risk of complications and relapses is very high and soccer players may return to his team with an incomplete neuromuscular recovery (Gómez-Barrena et al., 2008).
On the other hand, hamstrings function should be also taken into account.Mainly, the hamstring muscles in its eccentric phase are responsible for controlling the phase of walking as well as the function of decelerating speed (Small, 2008).Eccentric contraction is more efficient than concentric contraction because it requires less oxygen but the tension generated during eccentric contraction is much higher than with concentric, generating higher intrinsic forces within the muscle and hence predisposing to injury.Disruption results in loss of normal eccentric control.And from here, player's tracking should be continued to recover totally.In particular, it has shown that the intensity of sprint has been identified as the major mechanisms of injury hamstring muscle (Woods et al., 2004).In the present study, the distance covered at high intensity and sprint velocity, and also the accelerations and decelerations that the injured player displayed were larger than the intensities and distances of the rest of the team.Maybe this player, willing to recover promptly and to outstand, trained at too high intensities when the muscles were not totally recovered.
Different physical tests have been used to measure the physical condition of players after an injury, but these test do not reflect the external load or fatigue expressed in a football match (Small, 2008), and therefore the transferability of results could limit the test´s findings and could not be extrapolated to the match..According to this, the temporal pattern of the impact of hamstring strain during the match has revealed an increase in susceptibility to injury in the final minutes of matches (Woods et al., 2004) so it should take extra care at players reincorporated after injury to prevent relapse.
The limitation of the present study was that this is the description of a case study, particularly we analyze training load of a single player and consequently these results cannot be generalized.However, in our opinion the results are relevant and it would be desirable that more studies in a large number of players were conducted.For this, GPS devices may be an interesting tool in order to measure external load of injured players that start training with the team.
For the future, it would be very interesting to analyze the first phases of training days of players with some kind of injury, as this may have further implications regarding hamstring injury risk.

Conclusions
Hamstring injuries are common in football players because of the nature of the game itself (Fuller et al., 2006).Several studies have proposed the parameters that could cause the onset of the injury (Brockett et al., 2004;Orchard et al., 1997;Verrall et al., 2001).However, the impact of the weekly training in the recently incorporated player has not been analyzed yet.From the data of our study, we may suggest that training load should be controlled in order to prevent further stress of the affected muscle area using specific strategies to reduce intensity (Petersen & Hölmich, 2005;Petersen et al., 2011).
Moreover, the final phases of the rehabilitation preceding the return to sport of injured players must be performed on a specialized rehabilitation field under the control of specialists (Petersen & Hölmich, 2005) because an inadequate progression of the loads could put undue stress on players recently incorporated.
Therefore, players that join the team after suffering a hamstring injury should perform individual and progressive strength training exercises in order to achieve physical condition with similar values to those expressed by the team.

Figure 1 :
Figure 1: Dis tribution of the train ing ses sions after the hamstring injury and the relaps e.

Table 2 :
Average values (mean an d standard deviation) of the number of times in acceleratio n 1, acceleration 2 and acceleration 3 of the injured player and team.