Acute effects of small-sided games combined with running drills on internal and external loads in young soccer players

The purpose of this study was to compare the effects of regular small-sided games (SSGreg) and SSGs combined with running drills (SSGcom) on players’ internal and external loads. Eighteen young male soccer players (average age: 18.2 ± 0.5 years) participated in 3 vs. 3 and 4 vs. 4 games, under both SSGreg and SSGcom conditions. SSGreg bouts were played for 4 minutes without additional running drills, while SSGcom bouts consisted of 3 min 30 s SSG and 15 s running before and after the bout, making the duration of each bout 4 minutes. During all SSGs, measurements of heart rate (HR) responses as well as distances covered in four different speed zones – walking (WLK), low-intensity (LIR), moderate-intensity (MIR) and high-intensity running (HIR) – were recorded. Technical characteristics were monitored during the SSGs, and the rating of perceived exertion (RPE) and blood lactate (La-) responses were determined at the end of each SSG condition. Compared to the SSGreg in both 3 vs. 3 and 4 vs. 4 formats, the SSGcom condition resulted in higher La- and RPE responses (p < 0.05), greater distance covered at MIR and HIR speeds and greater total distance (p < 0.05). The results of this study show that replacing 30 s within the 4-min bouts of SSGs (both 3- and 4-a-side) by 2 x 15 s of running drills is effective in increasing internal (La- and RPE) and external loads (MIR and HIR) without a significant decrease in total passes and successful passes in young soccer players.     

Physical responses of different small-sided game formats in elite youth soccer players

A major use of small-sided games (SSGs) in soccer training is the concomitant development of game-specific aerobic fitness. We hypothesize that the SSG formats of 2 vs. 2, 3 vs. 3, and 4 vs. 4 players reveal game-like intensities and therefore are most adequate to increase game-specific aerobic fitness. Heart rate (HR), percentage of maximum heart rate (HRmax), blood lactate concentration (La), and time-motion characteristics of 17 elite male youth soccer players (aged 14.9 ± 0.7 years, V[Combining Dot Above]O2max 61.4 ± 4.5 ml·kg·min, HRmax 199.6 ± 7.3 b·min) were collected by global positioning systems while performing the SSG formats. Repeated-measures analysis of variance and effect sizes were calculated to demonstrate the differences between SSG formats. Highest physiological responses were obtained in 2 vs. 2 (HR: 186 ± 7 b·min, HRmax: 93.3 ± 4.2%, La: 5.5 ± 2.4 mmol·L) followed by 3 vs. 3 (HR: 184 ± 8 b·min, HRmax: 91.5 ± 3.3%, La: 4.3 ± 1.7 mmol·L) and 4 vs. 4 (HR: 179 ± 7 b·min, HRmax 89.7 ± 3.4%, La: 4.4 ± 1.9 mmol·L). Pronounced differences were found for most physiological parameters and for time spent in the speed zones "walking" (<5.3 km·h), "moderate-speed running" (10.3-13.9 km·h), and "maximum sprinting" (≥26.8 km·h). The findings suggest that all the formats reveal game-like intensities and are suitable for aerobic fitness improvements. However, we found pronounced demands on the anaerobic energy supply in 2 vs. 2, whereas 3 vs. 3 and 4 vs. 4 remain predominantly on an aerobic level and differ mainly in the HR response. We suggest using 3 vs. 3 for soccer-specific aerobic fitness training.     

Body size,maturation and motor performance in young soccer players: relationship of technical actions in small-sided games

The objective of this study was to investigate the relative contributions of body size, skeletal age, and motor performance variables with technical actions through an ecological model during small-sided soccer games, and the interaction of biological maturation with technical and motor performance in young players. In this cross-sectional study, eighty-two young players (14.4 ± 1.1 years), belonging to state-level soccer teams and divided by category (U-13 and U-15), were included. Players having an injury in the evaluation period were not included in the study. Measurements of body size, skeletal age (SA), motor tests, and technical actions in small-sided games (SSG) were performed (3 × 3 plus goalkeeper) in two periods (halves) of four minutes. Differences between age groups were found for SA (ES = -2.36), chronological age (ES = -3.89), body mass (ES = -2.09), height (ES = -1.90), and fat-free mass (ES = -2.09). Positive associations were found between body size (R = 0.43 to R = 0.48) and manipulation (R = 0.50 to R = 0.52) indicators and numbers of technical actions (CB and SS), except for stature with LB (R = -0.42) in the U-13 age group. In the U-15 category, skeletal age (R = -0.29 to R = -0.30) and body mass (R = -0.28 to R = -0.29) were negatively associated with the number of technical actions (RB, NB, LB, and OB) (P > 0.05) and positively with the balance with LB (R = 0.26). In conclusion, body size, SA, and motor performance influenced technical actions in SSG differentially in each category. U-13 heavier players and those with a better motor performance presented higher involvement due to the higher     

Comparison of the physiological responses to different small-sided games in elite young soccer players

The purpose of this study was to compare the blood lactate (La-), heart rate (HR) and percentage of maximum HR (%HRmax) responses among the small-sided games (SSGs) in elite young soccer players. Sixteen players (average age 15.7 6 0.4 years; height 176.8 6 4.6 cm; body mass 65.5 6 5.6 kg; VO2max 53.1 6 5.9 ml · kg(-1) · min(-1); HRmax 195.9 6 7.4 b · min(-1)) volunteered to perform the YoYo intermittent recovery test and 6 bouts of soccer drills including 1-a-side, 2-a-side, 3-a-side, and 4-a-side games without a goalkeeper in random order at 2-day intervals. The differences in La-, HR and%HRmax either among the SSGs or among the bouts were identified using 4 x 6 (games x exercise bouts) 2-way analysis of variance with repeated measures. Significant differences were found on La-, HR, and %HRmax among the bouts (p ≤ 0.05). The 3-a-side and 4-a-side games were significantly higher than 1-a-side and 2-a-side games on HR and %HRmax (p ≤ 0.05), whereas the 1-a-side game significantly resulted in higher La- responses compared to other SSGs. This study demonstrated that physiological responses during the 1-a-side and 2-a-side games were different compared to 3-a-side and 4-a-side games. Therefore, it can be concluded that a decreased number of players results in increased intensity during SSGs including 6 bouts. These results suggest that coaches should pay attention on choosing the SSG type and the number of bouts to improve desired physical conditioning of elite young soccer players in soccer training.     

Training elite youth soccer players: area per player in small-sided games to replicate the match demands

The aim was to determine the area per player (ApP, m² × player) in small- or large-sided games to replicate the official match demands in elite youth soccer players. Two hundred and twenty-eight players (U15 = 36, U16 = 48, U17 = 49, U18 = 37 and U19 = 58) were monitored during both training (12 183 individual samples) and matches (683 individual samples) across five seasons. Relative (m × min^-1) total (TD), high-speed running (HSR), very high-speed running (VHSR), sprint and acceleration/deceleration (Acc/Dec) distance were collected. Between-category and between-position comparisons were performed. Area per player was moderately correlated (P < 0.05) with TD (r = 0.401), large (r = 0.621) with HSR, and very largely with VHSR (r = 0.744) and sprint (r = 0.723). An inverse small (r = -0.232; P = 0.039) correlation for Acc/Dec was found. The area per player to replicate the match demands was 158 ± 18, 182 ± 32, 197 ± 37, 212 ± 42 and 156 ± 25 m² × player for TD, HSR, VHSR, sprint and Acc/Dec, respectively. Moderate to very large (ES: 0.79 to 4.66) differences in the area per player across metrics were observed, with sprint > VHSR > HSR > TD = Acc/Dec. Trivial to very large (ES: 0.01 to 2.67) between-category differences in area per player across the same metric were found, with U15 and U16 requiring a larger area per player than other age categories. These findings may help practitioners to recreate the desired external load outcomes with regards to positional match-play demands using specific area per player in small- or large-sided games in youth elite soccer players from U15 to U19.     

Small-sided games in amateur players: rule modification with mini-goals to induce lower external load responses

The aim of this study was to compare the acute physiological (i.e., heart rate-related variables) and neuromuscular responses (i.e., sprint and jump) and time-motion characteristics (i.e., external load variables) when modifying the game design (possession play vs. mini-goals without a goalkeeper) during 4-a-side in amateur senior football players. Male senior football players (n = 16) performed two formats of small-sided games (SSGs) in two different testing sessions (4-a-side with possession play and mini-goals rule). Differences in time-motion characteristics and physiological parameters of players were measured with the Global Positioning System (GPS), and tested before and after (pre- and post-SSG) for neuromuscular assessment. A repeated measures analysis of variance (ANOVA), with Bonferroni post-hoc test, showed that both SSG formats induced changes in sprint performance (before-after comparison) (p ≤ 0.05). Moreover, the results showed that the variables muscle oxygen saturation, rate of perceived exertion, 85–89% heart rate peak, total distance, total distances at low speed, total distances at high speed, m/min, accelerations at low speed, accelerations of ≥ 2.5 m.s^-2, maximal speed, and average speed were statistically significantly different among game conditions. The players’ performances are affected by the inclusion of mini-goals during 4 vs. 4 SSGs. The results provide useful information for training and task design that replicate specific physical demands (i.e., accelerations of ≥ 2.5 m.s^-2, total distances at high speed or total distances at low speed).     

格木幼苗对硝普钠-酸铝互作的生理响应

以格木（Erythrophleum fordii Oliv.）幼苗为材料,采用双因素完全随机设计实验方法,测定不同处理幼苗的光合色素和可溶性糖等生理指标,研究格木幼苗对硝普钠（SNP）-氯化铝（AlCl₃）互作的生理响应。结果显示,格木幼苗叶片中叶绿素a、叶绿素b和类胡萝卜素含量均在处理4（0.2 mmol/L AlCl₃、0.1 mmol/L SNP）时最高,在处理9（0.8 mmol/L AlCl₃、0 mmol/L SNP）时含量最低,而叶片中丙二醛（MDA）、游离脯氨酸含量则相反;叶片可溶性糖、可溶性蛋白含量在处理4时最高,在处理9时最低;处理10（0.8 mmol/L AlCl₃、0.1 mmol/L SNP）的超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性最高。施加SNP后,格木幼苗叶片中的叶绿素a、叶绿素b、类胡萝卜素、可溶性糖、可溶性蛋白含量及SOD、POD、CAT活性均显著高于未施加SNP处理。相关性分析表明,叶绿素a、类胡萝卜素、总叶绿素和可溶性蛋白含量等指标间均呈极显著正相关（P < 0.01）。本研究结果得出,低浓度AlCl₃（0.2 mmol/L）胁迫可促进格木幼苗的生长,添加外源SNP对高浓度AlCl₃（0.8 mmol/L）胁迫格木幼苗产生的毒害具有一定的缓解作用,可在格木幼苗的培育及抗性研究中推广应用。     

Effects of small-sided games and high-intensity interval training on physical performance in young female handball players

This study was designed to compare the effectiveness of small-sided handball games in combination with handball training (SSG group) versus high-intensity interval training in combination with handball training (HIIT group) on physical performance of young female handball players during pre-competitive period. Twenty-four young female handball players, who have a 6.17 ± 1.54 years training experience and competition in the national league participated in this study. SSG group (n = 12; age 16.06 ± 0.80 years, body mass 61.27 ± 3.68 kg, body height 1.64 ± 4.7 m, body mass index 22.7 kg/m²) while HIIT group (n = 12; 16.20 ± 1.28 years, body mass 62.46 ± 7.86 kg, body height 1.68 ± 6.8 m, body mass index 22 kg/m²). Both groups applied training programs twice-a-week for 8 weeks. Before and after the training programs physical performances were assessed: Countermovement jump (CMJ), Squat jump (SJ), Sprint on 0–10 m; Sprint on 0–20 m; Sprint on 0–30 m, Throwing medicine ball and total distance covered during the Yo-YoIRT1. After 8 weeks SSG and HIIT groups significantly improved CMJ, SJ, 0–20 m sprint, 0–30 m sprint, throwing medicine ball and Yo-YoIRT1 (p ≤ 0.05). However, significantly greater improvement was achieved in Yo-YoIRT1 (m) in HIIT group (28.40%) than SSG group (17.63%). These results indicate that SSG group and HIIT group equally improve of physical performances (jump, sprint and upper explosive strength) among young female handball players in pre-competitive period.     

Physiological Effects of Slot Play in Women

The purpose of this study is to describe the physiological responses occurring during slot gambling in 23 females with problematic and non-problematic gambling backgrounds in two sites: at a casino using their own money and at a casino laboratory without wagering money. Using the National Opinion Research Center Diagnostic Screen (NODS), 12 women were not-at-risk gamblers and 11 were at-risk, problem, or pathological gamblers. Blood pressure (BP), heart rate (HR), respiratory rate (RR), skin conductance (SC), and skin temperature (ST) were measured for 5 min before gambling (baseline), 10 min while gambling, and 5 min after gambling (recovery). In the casino, SBP (p = .001), DBP (p = .031), HR (p = .030), and RR (p = 004) rose during gambling and fell during recovery; ST rose throughout the study (p = .006). There were no differences between subjects based on NODS score. A total of 12 subjects were also studied in the laboratory. SBP (p = .004), DBP (p = .000); HR (p = .023); RR (p = .000) and SC (p = .002) rose during gambling and fell during recovery; ST rose throughout the study (p = .006). There were no significant differences by location. The observed effects suggest that females find slot play physiologically arousing, with or without financial stakes, because physiological changes were consistent with an arousal response.     

Physiological responses and time-motion characteristics of 4-a-side small-sided game in young soccer players: the influence of different team formation methods

ABSTRACT: K?klü, Y, Ers?z, G, Alemdaro?lu, U, A???, A, and ?zkan, A. Physiological responses and time-motion characteristics of 4-A-side small-sided game in young soccer players: The influence of different team formation methods. J Strength Cond Res 26(11): 3118-3123, 2012-The purpose of this study was to examine the influence of different team formation methods on the physiological responses to and time-motion characteristics of 4-a-side small-sided games (SSG4) in young soccer players. Thirty-two young soccer players (age 16.2 ± 0.7 years; height 172.9 ± 6.1 cm; body mass 64.1 ± 7.7 kg) voluntarily participated in this study. Anthropometric measurements, technical tests, and maximum oxygen uptake (V[Combining Dot Above]O2max) tests were carried out on the players. The SSG4 teams were then created using 4 different methods: according to the coaches' subjective evaluation (CE), technical scores (TS), V[Combining Dot Above]O2max (AP), and V[Combining Dot Above]O2max multiplied by TSs (CG). The teams thus created played 4 bouts of SSG4 at 2-day intervals. During the SSG4, heart rate (HR) responses, distance covered, and time spent in HRmax zones were recorded. In addition, rating of perceived exertion (RPE) and blood lactate level (La) were determined at the end of the last bout of each SSG4. Percent of HRmax (%HRmax), La, and RPE responses during SSG4 were significantly higher for teams chosen according to AP and CG compared with that according to CE and TS (p < 0.05). In addition, teams chosen by AP and CG spent significantly more time in zone 4 (>90% HRmax ) and covered a greater distance in the high-intensity running zone (>18 km·h) than did teams formed according to TS. Moreover, AP teams covered significantly greater total distance than TS teams did (p < 0.05). In conclusion, to spend more time in both the high-intensity HR zone and the high-intensity running zone, the teams in SSG4 should be formed according to the players' V[Combining Dot Above]O2max values or the values calculated using both the V[Combining Dot Above]O2max and technique scores.     

Invasion and expansion of cooperators in lattice populations: Prisoner's dilemma vs. snowdrift games

The evolution of cooperation is an enduring conundrum in biology and the social sciences. Two social dilemmas, the prisoner's dilemma and the snowdrift game have emerged as the most promising mathematical metaphors to study cooperation. Spatial structure with limited local interactions has long been identified as a potent promoter of cooperation in the prisoner's dilemma but in the spatial snowdrift game, space may actually enhance or inhibit cooperation. Here we investigate and link the microscopic interaction between individuals to the characteristics of the emerging macroscopic patterns generated by the spatial invasion process of cooperators in a world of defectors. In our simulations, individuals are located on a square lattice with Moore neighborhood and update their strategies by probabilistically imitating the strategies of better performing neighbors. Under sufficiently benign conditions, cooperators can survive in both games. After rapid local equilibration, cooperators expand quadratically until global saturation is reached. Under favorable conditions, cooperators expand as a large contiguous cluster in both games with minor differences concerning the shape of embedded defectors. Under less favorable conditions, however, distinct differences arise. In the prisoner's dilemma, cooperators break up into isolated, compact clusters. The compact clustering reduces exploitation and leads to positive assortment, such that cooperators interact more frequently with other cooperators than with defectors. In contrast, in the snowdrift game, cooperators form small, dendritic clusters, which results in negative assortment and cooperators interact more frequently with defectors than with other cooperators. In order to characterize and quantify the emerging spatial patterns, we introduce a measure for the cluster shape and demonstrate that the macroscopic patterns can be used to determine the characteristics of the underlying microscopic interactions.     

Short-term effects of on-field combined core strength and small-sided games training on physical performance in young soccer players

This study aimed to compare the effects of 6-weeks combined core strength and small-sided games training (SSG_core) vs. small-sided games (SSG) training on the physical performance of young soccer players. Thirty-eight amateur soccer players (age: 16.50 ± 0.51 years) were randomly assigned to either a SSG_core (n = 20) or a SSG group (n = 18). The SSG_core group performed upper and lower body core strength exercises combined with SSG including 2-, 3- and 4-a-sided soccer games third a week. The SSG group performed only the SSG periodization. Baseline and after the 6-week training period the Yo-Yo Intermittent Recovery Test level 1 (YYIRTL-1), 5–20-m sprint test, countermovement jump (CMJ), squat jump (SJ), triple-hop distance (THD), zigzag agility with ball (ZAWB) and without ball (ZAWOB), three corner run test (TCRT) and Y-balance test. The SSG_core group demonstrated meaningful improvements in 20 m sprint time (SSG_core: -9.1%, d = 1.42; SSG: -4.4%, d = 0.76), CMJ (SSG_core: 11.4%, d = 2.67; SSG: -7.7%, d = 1.43), SJ (SSG_core: 12.0%, d = 2.14; SSG: 5.7%, d = 1.28), THD (SSG_core: 5.0%, d = 1.39; SSG: 2.7%, d = 0.52) and TCRT (SSG_core: -3.7%, d = 0.69; SSG: -1.9%, d = 0.38). Furthermore, the SSG_core group demonstrated meaningfully higher improvement responses in both leg balance score (d = ranging from 2.11 to 2.75) compared with SSG group. These results suggest that the inclusion of core strength training to a SSG periodization is greatly effective to improve speed and strength-based conditioning in young soccer players.     

Injury incidence and risk factors in youth soccer players: a systematic literature review. Part I: epidemiological analysis

The analysis of the epidemiological data and the risk factors underlying injuries is crucial to promote prevention strategies in young soccer players. The objective of the present study was to perform a systematic literature review on the epidemiological data, described in the first part, and injury risk factors, presented in the second part. After electronic database searching, articles in line with the inclusion criteria were selected for the systematic review. Epidemiological data were extracted and discussed in this first part of the review. Data were grouped as follows: injury incidence, injury severity, and re-injury, injury types, injury mechanisms, and anatomical location. The principal findings of this first part of the review are as follows: (1) injury incidence is higher in older players and during matches than during training; (2) sex and maturity status may increase risk of injury; (3) male soccer players are more prone to muscle strains and ligament sprains while female players suffer more ligament sprains; (4) most injuries are located in the ankle and thigh in young male soccer players, and in the ankle and knee in female players; (5) severe injuries are less frequent but the incidence increases in older players. Re-injuries represent only a small percentage. Although soccer is considered a safe sport, many injuries are recorded in young soccer players every year. Injury predisposition changes in relation to age, sex, and biological age. Coaches and physical trainers should be aware of individual differences in order to promote prevention strategies and personalised training.     

Warm-up optimization in amateur male soccer players: A comparison of small-sided games and traditional warm-up routines on physical fitness qualities

The aim of this study was to compare the effects of small-sided soccer games (SSSGs) and traditional warm-up (TWU) routines on physical fitness qualities in soccer players. Following a between-subject, randomized design, amateur-level soccer players were assigned to a SSSG warm-up (n = 10; age: 19.3 ± 2.8 years) or TWU group (n = 10; age: 19.3 ± 2.4 years). Players completed multiple trials of 10-m and 30-m linear sprints, change-of-direction speed (CODS) tests, and countermovement jumps (CMJ) prior to and following the warm-up routine. Separate mixed ANOVAs were performed to assess group effects (SSSG vs. TWU), time effects within each group (pre- vs. post-warm-up), and their interaction for each physical fitness quality. No significant interaction effects were observed for any dependent variable. Significant improvements were evident between baseline and follow-up measurements for 10-m sprint time (p = 0.002, Hedges’ g effect size [g] = 0.59) and CMJ variables (height: p = 0.016, g = 0.20; power: p = 0.003, g = 0.19; force: p = 0.002, g = 0.14) in the TWU group and for CODS performance time (p = 0.012, g = 0.51) and CMJ variables (height: p < 0.001, g = 0.46; power: p = 0.002, g = 0.35; force: p = 0.001, g = 0.27) in the SSSG warm-up group. Both SSSG and TWU protocols improved selected physical fitness qualities with SSSG more effective at improving CODS and CMJ performance, and TWU more effective at improving linear speed. Soccer coaches may choose between SSSG or traditional warm-up activities according to player needs and preferences; however, the superior effects of SSSG suggest it might offer greater benefits than TWU in preparing players for optimal physical output.     

Physiological responses induced by copper bioaccumulation in <Emphasis Type="Italic">Eichhornia crassipes</Emphasis> (Mart.)

Eichhornia crassipes (Mart.) has strong ability to remove Cu²⁺ from copper-contaminated water. Physiological responses in E. crassipes exposed to known concentrations of Cu²⁺ were examined in this study, and demonstrated that E. crassipes could accumulate 314 mg kg⁻¹ dry weight of Cu when exposed to 5 mg l⁻¹ of Cu²⁺ for periods up to 14 d. However, there were marked changes in physiology of the plant commencing at Cu²⁺ concentrations of 1 mg l⁻¹. Results of this study showed that E. crassipes could tolerate moderate concentrations (i.e. 0.5 mg l⁻¹) of Cu²⁺, without significant changes in photosynthetic pigment concentrations, while high concentrations (i.e. 5 and 10 mg l⁻¹) of Cu²⁺ resulted in substantial loss in pigment concentrations. Increases in malondiadehyde (MDA) content were also demonstrated in plant exposure to high Cu²⁺ concentrations. Soluble protein content increased to a level slightly higher than the control at <0.5 mg l⁻¹ of Cu²⁺, but then decreased with exposure to >1 mg l⁻¹ of Cu²⁺. Our results suggest that E. crassipes has a substantial capacity to accumulate copper when cultivated at moderate concentrations of Cu²⁺, without marked changes in its physiology. The findings indicate that E. crassipes is a promising possibility for phytoremediation of moderately Cu-contaminated water bodies. Handling editor: S. M. Thomaz     

Effects of 1 vs. 2 sessions per week of equal-volume sprint training on explosive,high-intensity and endurance-intensive performances in young soccer players

The study aimed to evaluate the effects of 1 vs. 2 sessions per week of equal-volume sprint training on explosive, high-intensity and endurance-intensive performances among young soccer players. Thirty-six young male soccer players were randomly divided into 2 experimental groups that performed either a single weekly sprint training session (ST1, n = 18, age: 17.2 ± 0.8 years) or two weekly sprint training sessions (ST2, n = 18; age: 17.1 ± 0.9 years) of equal weekly and total volume, in addition to their regular soccer training regimen. Linear sprinting (10 m, 20 m, 30 m, and flying 10 m), T-test agility, countermovement jump (CMJ) and maximal oxygen consumption were assessed one week before (T1), in the middle (T2) and immediately after the 10 weeks of training (T3). A large magnitude and statistically significant main effect for time was found in all the assessed variables after both training interventions (all p < 0.001; ES ≥ 0.80). No main effect was observed between the 2 groups at any time in linear sprinting, T-test or CMJ test (p > 0.05; ES < 0.20). A significant interaction effect (F = 4.05; p = 0.04, ES = 0.21) was found for maximal oxygen consumption with ST2 inducing better performance than ST1 (p = 0.001; ES = 1.11). Our findings suggested that the two sprint training frequencies were effective in enhancing explosive, high-intensity and endurance-intensive performances. However, it is recommended for coaches and fitness coaches to use a biweekly sprint training modality as it was found to be more effective in improving endurance-intensive performance.     

Injury incidence and risk factors in youth soccer players: a systematic literature review. Part II: Intrinsic and extrinsic risk factors

Injury is defined as a complex phenomenon determined by the non-linear interaction of several intrinsic and extrinsic factors. The objective of the present study was to perform a systematic literature review on the injury risk factors in young soccer players. After electronic database searching, articles in line with the inclusion criteria were selected for the systematic review. Injury risk factor data were extracted and grouped in intrinsic and extrinsic risk factors. The main findings of the current review are as follows: (1) alteration in neuromuscular control such as limb asymmetry and dynamic knee valgus are important intrinsic risk factors; (2) maturation status may impair neuromuscular control and increase the risk of injury; (3) fatigue and poor recovery contribute to the onset of overuse injuries; (4) the impact of anthropometric factors is still unclear; (5) previous injuries increase the risk of re-injuries; (6) highly skilled players are more exposed to risk of injuries; (7) high external workloads increase the risk of injuries; (8) playing position, as well as sport specialization, exposes young soccer players to greater injury risk. Many factors (e.g., neuromuscular control, training load, maturity status) can modify the susceptibility to injury in young soccer players. Being aware of the complex interaction between these factors is essential to identify players at higher risk of injury, develop adequate prevention strategies, and from a scientific point of view move from a reductionist to a complex system approach.     

Allelopathic Effects,Physiological Responses and Phenolic Compounds in Litter Extracts of Juniperus rigidaSieb. et Zucc.

The allelopathic effects of Juniperus rigida litter aqueous extract (LE) on wheat and Pinus tabuliformis were studied, as well as the physiological responses to the extract. High concentration LE (0.10 g Dw/ml) significantly inhibited the seed germination and seedling growth in receptor plants. The chlorophyll content and root activity in the wheat seedlings were reduced significantly across all treatments; however, those were more prominently reduced at high concentration (0.10 g Dw/ml) but received little stimulation at low concentration (0.025 g Dw/ml) in P. tabuliformis. The content of malonaldehyde (MDA) increased with increasing concentrations of LE, except at 0.025 g Dw/ml. Activities of antioxidant enzymes (POD, CAT and SOD) in receptor plants were all significantly inhibited at high concentrations but stimulated at low concentrations. These results demonstrate that the aqueous extract from J. rigida litter has allelopathic potential. Various phenolic compounds were identified in litter aqueous extract and litter ethanol extract by HPLC. The phenolic compound content in the aqueous extract was significantly lower than that in the ethanol extract. Chlorogenic acid and podophyllotoxin were the predominant phenolic compounds in both types of litter extracts. These findings suggest that the seed germination and seedling growth of P. tabuliformis and wheat would be inhibited when planted near large amounts J. rigida litter.     

Physiological responses of Pogonatum cirratum subsp. fuscatum living in different habitats to simulated nitrogen deposition

The effects of nitrogen (N) deposition on Pogonatum cirratum (Sw.) Bird. subsp. fuscatum (Mitt.) Hyvoenen, a species of moss widely distributed in South China, were investigated. Plots subjected to a gradient of N treatments were established in 3 habitats with different illumination and humidity conditions. N was sprayed onto plots with NH₄NO₃ solutions, at doses equivalent to 20, 40 and 60 kg N ha^?1, in 4 applications during May 2006 and January 2007. The results suggest that high N deposition affects both carbon (C) and N metabolism of P. cirratum subsp. fuscatum, as well as the interaction between them. On the other hand, the sensitivity of the moss varied according to the humidity and light conditions. Moss in a habitat with high humidity and moderate light was more tolerant to an N deposition increase than moss in a habitat with low humidity and low light, as the latter was extremely sensitive to an increase in N deposition.