The Effects of Weekly Recreational Soccer Intervention on the Physical Fitness Level of Sedentary Young Men

Recreational soccer (RS) has a great potential to improve the physical fi tness levels of diverse populations when performed two to three times per week. However, to date, only Beato and collaborators have examined the eff ects of once-a-week RS on physical fi tness, even though this frequency is widespread among participants. Th us, this study aimed to investigate the eff ect of weekly performed RS intervention on components of physical fi tness in sedentary young men. Twenty-healthy men aged 20-27 years were randomly assigned to a soccer (n=10) group or a control (n=10) group. Participants in the soccer group played a 60-min. small-sided soccer game once-a-week for eight weeks. Before and aft er the intervention period, body composition, aerobic fi tness, blood pressure, anaerobic performance and isokinetic leg strength were assessed. Aft er eight weeks of the once-a-week intervention period, in the soccer group, body fat and thickness of skinfolds were signifi cantly decreased (p<0.05). Peak oxygen uptake, running distance, squat and countermovement jump (p<0.01), concentric quadriceps and eccentric hamstring strength were also improved only in the soccer group (p<0.05). In contrast, other variables, including body mass (BM), body mass index (BMI), fat-free mass (FFM), heart rate responses, blood pressure, and anaerobic performance remained the same as before the intervention period (p>0.05). Participating in weekly RS programme can lead to some health and performance benefi ts. However, the people who wish to further improve their health status and performance level should increase the frequency of RS activity.


Introduction
It is well established that physical activity is related to decreased risk of several chronic diseases, improved physical capacity, and increased quality of life.Th erefore, physicians focus on promoting regular physical activity habits that will be retained throughout the lifespans of their patients.In this context, RS has a great potential to improve the health and physical fi tness levels of diverse populations.Th is may because the dynamic nature of soccer not only provides opportunities to develop diff erent aspects of physical fi tness of participants, but it also contains positive motivational and social factors that contribute to the maintenance of a physically active lifestyle (Andersen et al., 2010).
Multiple studies of diverse populations have demonstrated that average cardiovascular load during RS exceeded 80% heart rate (HR) maximum even in elderly individuals (Randers et al., 2010b;Randers et al., 2012;Aslan, 2013).Moreover, a recent study demonstrated that during RS 20-30% of total time spend with an HR above 90% of the maximal HR (Randers et al., 2010b).Furthermore, RS is an intermittent activity including many high-intensity actions (sprinting, turns, jumping, kicking, accelerations, and decelerations) the would be expected to stimulate positive adaptations in several physical fi tness parameters.However, the number of training sessions or weekly training volume and the length of the intervention period are also the most vital components to achieve morphological and physiological adaptations.In recent studies, it was demonstrated that 12 weeks of soccer practice performed three 60 min sessions per week improved maximal aerobic power, jumping performance, fl exibility, and body composition parameters in healthy untrained young males (Milanovic, Pantelic, Kostic, Trajkovic, & Sporis, 2015b;Milanovic, Pantelic, Sporis, Mohr, & Krustrup, 2015c).
Similarly, Randers et al. (2012) demonstrated that 12 weeks of soccer games three days per week increased the physical fi tness level and cardiovascular health status of middle-aged homeless men, represented by VO 2 max, incremental cycle test performance, fat percentage, and LDL cholesterol.Krustrup et al. (2010a) also reported similar fi ndings in a study of untrained men when the small-sided RS was performed two to three times per week for 12 weeks.Th ere is also experimental evidence for the eff ectiveness of RS in the improvement of the physical fi tness of diff erent population groups, including premenopausal women (Krustrup et al.,2010b) mild to moderate hypertensive middle-aged men (Andersen et al., 2010) and prepubertal children (Krustrup et al., 2014) when the activity was performed two to three days a week.
In contrast, a lack of time is one of the most commonly reported barriers to exercise participation (Gibala, Little, MacDonald, & Hawley, 2012).Th erefore, this may be the reason that a single RS session a week is as common or even more common among participants.A recent study demonstrated that a single RS session a week accounted for 50% of the ACSM-recommended lowest level of energy expenditure (Beato, Impellizzeri, Coratella, & Schena, 2016).However, to our knowledge, there is only one study investigating the eff ect of a single RS session a week on physical fi tness levels (Beato, Coratella, Schena, & Impellizzeri, 2017) and there is still a great deal of uncertainty about the threshold activity levels that can enhance health and performance level of young individuals (Hiruntrakul, Nanagara, Emasithi, & Borer, 2010).Th e time-effi cient threshold theory proposes that intensity coupled with minimal frequency and duration of training may provide the requisite stimulus (Winett & Carpinelli, 2000).Th erefore, the purpose of this study was to investigate the eff ects of weekly performed RS intervention on the components of physical fi tness in young sedentary males.Participants in the soccer group played a one-hour small-sided soccer game once-a-week for eight weeks on a 30-50-metre artifi cial grass pitch (excluding goalkeepers, each team comprised fi ve players), whereas participants in the control group continued their routine daily life.During the games, HR responses were recorded with a sampling frequency of 5 s using a Polar HR monitor (RS800 CX, Polar Electro, Finland) to determine the game intensity throughout the intervention period.Th en intensity was quantifi ed as the mean percentage of HR reserve (%HRres).%HRres was calculated according to the formula of Karvonen (1957).

Participants and Procedure
[(%HRres=(match mean HR-resting HR)/(HRmax-resting HR)x100].Before and aft er the eight weeks of intervention, the following tests were administered to all participants on separate days in the following order: I) resting HR, systolic blood pressure (SBP) and diastolic blood pressures (DBP), anthropometric measurements, squat jump (SJ) and countermovement jump (CMJ) tests, II) Wingate anaerobic test (WAnT), III) isokinetic leg strength test, IV) the maximal multistage 20-m shuttle run test (SRT).Th e last three tests were conducted at least one day apart from each other to allow for adequate recovery.All of these tests were completed within the one-week period in the same order, before the beginning of the intervention (pre-test) and aft er the completion of the eight weeks intervention period (post-test).All tests were conducted under indoor conditions at the same time of day, and the participants were familiar with these test procedures before actual testing.All subjects were instructed to abstain from eating for at least two hours before the tests.In addition, they were asked to maintain their nutritional habits and daily lifestyle throughout the intervention protocol.Th e average temperature and humidity during the pre-test were 18.2±1.7˚Cand 63.7±4.18%,respectively (Hanna Instruments,HI 8564,Italy).Corresponding values during the post-test were 21.3±1.3˚Cand 67.1±2.57%,respectively.Th e study received ethical approval from the human ethics committee of local university (2013/07), and informed consent was obtained from all participants.

Anthropometric Measurements
Height and BM were measured using a calibrated electronic scale (Seca, France) to the nearest 0.1cm and 0.1kg, respectively, with the subject lightly dressed without shoes.BMI was calculated as BM (kg) divided by height (m²).Th e thickness of eight skinfolds (biceps, triceps, subscapular, chest, suprailiac, abdominal, thigh and medial calf) was measured with a skinfold calliper (Holtain Ltd, UK) to the nearest 0.2 mm, on the right side of the body, using standard procedures (Lohman & Roche, 1988).Th e sum of the eight skinfolds was used as a total indicator of fatness.Alternatively, the sums of arm, trunk, and leg skinfolds were also used as a regional indicator of fatness.Moreover, the percentage of body fat (%BF) was calculated from the Faulkner equation (Faulkner, 1968).Fat-free mass (FFM) was calculated from %BF and BM.One investigator performed all measurements to avoid any inter-observer diff erences.

Determination of Resting Heart Rate and Blood Pressures
Resting HR was recorded for 10 minutes in a supine position using HR monitor (RS800 CX, Polar Electro, Finland).Th ereaft er, the minimum HR observed during this period was used as the resting HR value (Dellal et al., 2012).SBP and DBP were measured three times on the left arm at the level of the heart (Omron Healthcare Co. Ltd, Kyoto, Japan).All the measurements were completed in the morning at 8:00-10:00 am.Th e SBP and DBP were determined as the average of three recordings in mmHg.Th e mean arterial blood pressure (MAP) was calculated by the following formula: [(SBP-DBP)/3+DBP] (Elliott, Sale, & Cable, 2002).

Squat and Counter Movement Jump Tests
Before the tests, each subject performed a standardized warm-up protocol.SJ and CMJ performances were measured using an electronic timing mat (Ergo Tester, Italy).SJ was performed from a half squatting position with hands placed on hips.Th e participants were asked to remain motionless for 2 s, and then they jumped vertically for maximal height.Th e participants were not allowed to countermovement at the start of the jump.CMJ was administered while the participants started from an erect standing position.Th en, they made a downward countermovement to the same starting position as the SJ and jumped vertically for maximum height.All participants performed three consecutive trials, and the highest value for each jump was used.

Wingate Anaerobic Test
Th e WAnT was performed on a computerized cycle-ergometer (Monark 834E, Sweden).Before the test, each subject was informed about the protocol.Th e seat height was adjusted for each subject, and the feet were strapped to the pedals.Aft er a standardized 3-min warm-up, the subject rested for 5 min (Inbar, Bar-Or, & Skinner, 1996).Th e subject was instructed to perform the test as fast as possible.Th en the WAnT was initiated against minimal resistance.Following 3-4 seconds, the predetermined resistance (75 gr.kg -1 ) was applied, and the computer was activated.Verbal encouragement was given throughout the 30-s test.Aft er the test, the subject was instructed to pedal slowly to assist recovery.Th e highest and the lowest power output obtained in the 30-s were defi ned as peak and minimum power, respectively, and the mean power was the average of all values obtained during the test.A fatigue index was also calculated (Inbar et al., 1996).Power outputs were expressed in absolute (W) and relative units (W•kg -1 ).

Isokinetic Leg Strength Test
Isokinetic strength data were recorded with the Biodex System-4 Dynamometer (Biodex Medical Inc, Shirley, NY) to assess the strength of the muscle groups in accordance with the Biodex System manual (Biodex Multi-Joint System Pro, 2017).Strength measurements were preceded by a fi ve-minute standardized warm-up on a cycle ergometer at 80W.Each subject then performed lower extremity fl exibility exercises, including quadriceps, hamstring, and calf stretches.Every stretching exercise was performed three times and held for 15 s.Subjects were tested for both concentric and eccentric quadriceps (Q con & Q ecc ) and hamstring (H con & H ecc ) strength on dominant legs at 60°/s.Th e dominant leg was defi ned as the preferred kicking leg.Th e testing criteria consisted of three maximal concentric and eccentric eff orts; meanwhile, three submaximal knee extension and fl exion contractions were allowed before the real tests.A 3 min.rest was allowed for between each test.Peak torque (PT), PT to body weight (PT/BW), conventional (H con /Q con ) and dynamic control (H ecc /Q con ) ratios were chosen for strength analysis.

Maximal Multistage 20-m Shuttle Run Test
Aerobic fi tness was assessed using SRT according to the one-min protocol (Leger, Mercier, Gadoury, & Lambert, 1998).During the SRT, HR was recorded continuously every 5-s period with a Polar HR monitoring system.Peak HR was determined for each subject as the highest HR recorded during any 5-s period of the SRT.Moreover, HR responses to submaximal running speeds were also calculated for each subject.At the end of the SRT, the total number of completed shuttles was recorded for each subject.Th ereaft er, the peak oxygen uptake (VO 2 peak) was calculated from the following formula: [VO 2 peak=61.1-(0.462× age)-(0.862x BMI)+(0.192× number of shuttles completed)] (Matsuzaka et al., 2004).In addition, peak running distance (RDpeak) (i.e., number of completed shuttles multiplied by 20-m) during the SRT was also calculated for each subject and used in the further analysis.

Statistical Analysis
All data were presented as mean value ± standard deviation (sd).Th e assumption of normality and homogeneity of variance were verifi ed using the Kolmogorov-Smirnov and Hartley's F max test, respectively.Th e data were analyzed with separate 2×2 (groups and time) mixed repeated-measures ANOVA design.Th e SPSS's syntax language was used to analyse the simple eff ect of time within levels of group variable.All statistical analysis was performed using SPSS for Windows, version 15.0 (SPSS Inc., Chicago, USA).Th e level of statistical signifi cance was set at p<0.05 for all analyses.

Results
Th e mean intensity of the soccer small-sided games was 172.7±1.9 b.min -1 (within the range of 169.6 to175.1 b.min -1 ), which corresponded to 80.6±4.3% of the HRres (Figure 1).Th ere was no signifi cant diff erence in all parameters between the soccer and the control group before the intervention period (Table 1 and Table 2).Aft er the weekly intervention period, % BF (F 1,18 =4.784, p<0.05), the sum of eight skinfolds (F 1,18 =4.667, p<0.05) and arm skinfolds (F 1,18 =8.742, p<0.01) were signifi cantly reduced in the soccer group, but unchanged in the control group (Table 1).Moreover, BM, BMI, FFM, sum of the trunk and leg skinfolds, resting HR and MAP values also tended to reduce aft er the intervention period in the soccer group, but the diff erences were not statistically signifi cant (p>0.05)(Table 1).
Relative to the control group, the soccer group showed a signifi cant improvement in their endurance capacity on the SRT following the weekly intervention period (Table 1).Aft er eight weeks of match-play, in the soccer group, VO2peak (F 1,18 =21.743, p<0.001) and RDpeak (F 1,18 =15.354, p<0.001) increased by 6.3% and 16.4%,  respectively, whereas in the control group no signifi cant changes were observed in VO2peak or RDpeak (p>0.05).Moreover, submaximal HR responses also showed a slight tendency to decrease aft er the intervention period in the soccer group (Table 1), though not signifi cantly (p>0.05).
Th e soccer group showed a signifi cant improvement in its SJ (F 1,18 =8.493, p<0.01) and CMJ (F 1,18 =8.089, p<0.05) performance following the weekly intervention period (Table 2).Aft er eight weeks of match-play, in the soccer group, SJ and CMJ heights increased by 9.5% and 9.1%, respectively, whereas in the control group no signifi cant changes were observed in jump heights.Furthermore, peak and minimum power outputs also showed a slight tendency to increase aft er the intervention period in the soccer group (Table 2), though not signifi cantly (p>0.05).
Th e results indicated that aft er the training period Q con PT (F 1,18 =5.512, p<0.05) and PT/BW (F 1,18 =5.846, p<0.05) and H ecc PT (F 1,18 =4.588, p<0.05) and PT/BW (F 1,18 =6.064, p<0.05) values increased in the soccer group, but no changes were observed in the control group (Figure 2).Furthermore, conventional and dynamic strength control ratios remained the same aft er eight weeks of interventions in both groups (p>0.05)(Table 2).

Discussion
Th is study examined whether once-a-week RS for eight weeks infl uenced the physical fi tness status of sedentary young men.To our knowledge, only one previous study (Beato et al., 2017) has examined the eff ect of a single one-hour RS intervention a week on the level of physical fi tness.However, while Beato et al. ( 2017) examined the eff ects of RS on health-related physical fi tness components in middle-aged males, the present study focuses on both health-and performance-related physical fi tness components in young males.Th us, the main contribution of this study concerning the existing literature is that it provides information about whether the components of health-and performance-related physical fi tness of young sedentary individuals are infl uenced by such a low frequency of soccer activity.Th e main fi ndings revealed that although eight weeks of one-hour weekly small-sided RS resulted in the improvement of several physical fi tness components, including %BF, aerobic endurance, and muscular strength in sedentary young men, it could not produce suffi cient stimulus on resting and submaximal HR responses and blood pressure, which can be considered as an important indicator of cardiovascular health status.In addition, the current study indicated that weekly RS intervention over eight weeks failed to improve anaerobic energy turnover.
A recent review and meta-analysis indicated that small-sided RS with training frequency of two to three sessions per week positively aff ects aerobic fi tness level regardless of the age, sex and health status of the participants (Hammami et al., 2016;Milanovic, Pantelic, Covic, Sporis, & Krustrup, 2015a).Krustrupt et al. (2009), in a study conducted on healthy untrained males, indicated that VO 2 max improved 7% aft er two to three weekly one-hour small-sided RS sessions over four weeks, and additional improvements were observed from 4 to 12 weeks.Th us, it can be suggested that the eff ectiveness of RS on aerobic endurance begins early in the intervention period.Similarly, the present study indicated that there were 16.4% and 6.3% increases in RDpeak during the SRT and estimated VO 2 peak, respectively.Similar to the present fi ndings, Beato et al. ( 2017) reported 4.4% and 5.95% increase in VO 2 max and maximal aerobic speed, respectively, aft er 12 weeks of weekly performed RS in middle-aged males.Th ese fi ndings recommended that RS is an eff ective activity to improve aerobic endurance level of participants even performed only once a week.Unfortunately, oxygen consumption could not be determined directly in this study.However, enhanced maximal oxygen consumption may be a plausible suggestion for the increase in aerobic endurance.In fact, the activity profi le during small-sided RS is similar to interval training, which is proven to be an eff ective method for VO 2 max improvement (Milanovic, Sporis, & Weston, 2015d).Notably, high-intensity periods during RS (time spend over 90% HRmax) elicits greater improvement in VO 2 max compared with aerobic running (Krustrup et al., 2009).Th e eff ectiveness of RS on aerobic fi tness was also indicated by Randers et al. (2010a) who observed that VO 2 max can be maintained over a long time even though the training frequency reduced from 2.4 to 1.3 sessions per week.
It was demonstrated that the untrained males participating in the soccer training programme, two to three times weekly for 12 weeks, each lasting 60 min, had a decrease in resting HR and HR during submaximal continuous running.In addition, in the same study, it was observed that regular soccer training resulted in 8 and 5 mmHg drops of SBP and DBP, respectively.Similar observations were made by Anderson et al. (2010) and Randers et al (2010a) in untrained males when RS was performed two to three weekly over 12 weeks.Beato et al. ( 2017) also indicated benefi cial eff ects of RS on SBP and MAP performed only once a week.In contrast, the present results showed no-signifi cant decrease in either blood pressure or HR responses at rest and during submaximal exercise aft er the intervention period.However, the observed decrease of 3.9 mmHg (89.6 vs 85.7) in MAP in this study is in accordance with the fi ndings of Beato et al. ( 2017) and Randers et al. (2010a) who indicated 3 mmHg and 5 mmHg drops in MAP, respectively, over 12 weeks of football training in untrained males.
In contrast, the extents to which values can be changed by training depend on subjects' levels before the initiation of the training programme.In this study, before the initiation of the intervention period, the SBP, DBP, and resting HR values of our participants were within the normal range or at somewhat lower level (Table 1), which may attenuate the adaptation process.Cornelissen and Fagard (2005), in a random eff ects model meta-analysis study, indicated that the reduction of SBP and DBP were higher in hypertensive study groups compared with normotensive study groups.Similarly, Krustrup et al. (2009) observed that the reduction of resting blood pressure was more pronounced in the seven subjects with the highest initial values.Randers et al. (2012) also indicated that although blood pressure was unaltered aft er 12 weeks of street soccer (2.2 per week), DBP was lowered for all participants with previous values greater than 75 mmHg.Th erefore, future studies may be needed to further examine the eff ectiveness of weekly RS intervention on blood pressure and HR responses in diff erent populations, especially including those who are hypertensive and who have initially high resting HR values.
According to the present results, the sum of eight skinfolds and %BF only slightly decreased in the soccer group aft er the intervention period, but no signifi cant changes were observed in BM, BMI, or FFM.In agreement with the present results, a recent study demonstrated that once-a-week 1 h performed RS would not produce substantial and signifi cant improvements in body weight, %BF, and BMI in middle-aged males (Beato et al., 2017).Th e fi ndings of these two studies can be interpreted as once a week RS intervention is not a proper strategy when the major aim of participants is to reduce body weight and % BF.However, a previous study conducted on young adult men revealed that 12 weeks of three 60 min soccer sessions per week led to considerable decrease on BM, BMI, and %BF (Milanovic et al., 2015b).Similarly, a recent meta-analysis concluded that two weekly 60 min RS interventions lasting 12-16 weeks are likely to cause a decrease in total fat mass of 1-3 kg (Milanovic et al., 2018).In addition, it was demonstrated that RS intervention can increase lean body mass when performed two to three times weekly over 12 weeks in untrained males and females (Krustrup et al., 2009;Krustrup et al., 2010a;Krustrup et al., 2010b).Th erefore, it seems that the eff ect of RS activity on body composition is unsurprisingly related to the frequency of weekly sessions/total volume and length of the intervention period.
Previous studies investigating the eff ectiveness of RS on the neuromuscular system showed that this type of activity potentially increases muscular strength when the exercise is performed two to three times weekly over 12 weeks, or for longer periods of time (Krustrup et al., 2009;Krustrup et al., 2010a;Krustrup et al., 2010b).
In a study of young men participating in RS two to three times a week over 12 weeks, Krustrup et al. (2010a) observed a signifi cant increase in the quadriceps muscle mass, mean fi bre area, lean body mass as well as maximal isometric hamstring strength.Moreover, a recent meta-analysis indicated a positive eff ect of RS on muscular fi tness evaluated as jump performance (Milanovic et al., 2018).Similarly, according to the present results, the soccer group increased their Q con , H ecc strength and jumping performances aft er the intervention period.Indeed, the soccer practice involves intermittent physical activity and variety of skills requiring running, sprinting, jumping and kicking.All these activity patterns are the quadriceps-dominant activities while the hamstring plays an important role in the stability of the knee joint complex (Fried & Lloyd, 1992).Furthermore, the hamstring muscles contract eccentrically during soccer activities, such as kicking, sprinting or changing of directions, in order to decelerate the forward movement of the leg.Th erefore, improvements in Q con and H ecc strength could be explained by the contraction characteristics of muscle groups during soccer activities.However, because of the lack of increase in FFM observed in this study, it is more likely that the strength gains may associate with an increase in neural recruitment rather than muscular hypertrophy.
Th e present results also showed that conventional and functional strength ratio evaluations did not diff er aft er an eight-week intervention period.Th e conventional ratio has been claimed to be one of the many variables that contribute to knee joint stability and control (Aagaard, Simonsen, Magnusson, Larson, & Dyhre-Poulsen, 1998; Kellis & Baltzopoulus, 1998).Th e practical signifi cance of the functional ratio is related with the functional tasks (i.e., vertical jump) or dynamic knee joint movements (Coombs & Garbutt, 2002).Although there were signifi cant increases in Q con and H ecc strength aft er the intervention period, the symmetric strength improvement repressed the development of the functional strength ratio.In this study, it is also apparent that symmetric strength gains functionally resulted in signifi cant improvement in vertical jump performances (Table 2).Th ese fi ndings indicated that weekly soccer practice also had a benefi cial eff ect on functional movement tasks.However, the amount of increase in jumping performance observed in this study (9.1-9.5%, for CMJ and SJ, respectively) is lower compared to that in the study of Milanovic et al. (2015c).(12.1-14.8%for CMJ and SJ, respectively) where training performed three times a week for 12 weeks.
In conclusion, once-a-week RS interventions over eight weeks positively infl uenced the physical fi tness level of sedentary young men by lowering % BF and increasing aerobic endurance, jumping performance, Q con and H ecc strengths.In contrast, it could not produce suffi cient stimulus to decrease resting and submaximal HR, blood pressures, anaerobic performance, Q ecc and H con strengths.However, the participants of this study were already physically fi t healthy young subjects and the intervention duration somewhat lower than the previous studies.Th erefore, remarkable initial values in combination with a relatively short intervention period might resulted in an attenuated adaptation response.Nonetheless, even though the present fi ndings recommended that RS performed once a week provides substantial improvement in aerobic endurance and leg strength parameters, the participants who wish to further improve their health and performance levels should increase the weekly frequency of RS activity.Since the magnitude of adaptations can be infl uenced by several factors, including age, gender, and health status (Milanovic et al., 2018), the fi ndings of this study cannot easily be extended to other populations.Th erefore, future studies are needed to examine the health and performance eff ects of single RS a week in a diverse population.

FIGURE 1
FIGURE 1 Game intensity throughout the 8-weeks of intervention period Twenty sedentary healthy men not previously involved in any systematic training participated in this study.Participants were randomly assigned either to a soccer group [n=10, age 22.1±1.8years, height 172.6±4.4cm,BM 70.8±3.9kg]or to a control group [n=10, age 23.4±1.6 years, height 173.9±4.7cm,BM 72.4±4.7kg].

TABLE 1 Body
composition, blood pressures, heart rate and aerobic endurance variables before and after the 8 weeks of weekly intervention in the soccer and control groups.Data are presented as means ± sd EFFECTS OF WEEKLY RECREATIONAL SOCCER INTERVENTION | A. ASLAN ET AL.

TABLE 2
Anaerobic performance variables and isokinetic strength ratios before and after the 8 weeks of weekly intervention in the soccer and control groups.Data are presented as means ± sd Note. *signifi cantly higher than pre-test value at p<0.05, **signifi cantly higher than pre-test value at p<0.01, SJ: squat jump, CMJ: countermovement jump, H con /Q con : concentric hamstring/quadriceps, H ecc /Q con : eccentric hamstring/ concentric quadriceps.FIGURE 2 Weekly recreational soccer intervention induced changes in isokinetic strength performance over 8 weeks Note.*signifi cantly high er than pre-test values at p<0.05