Muscle strength and flexibility in different positions of soccer players

Prediction of ACL-tear by lower limbs muscle strength and flexibility: a prospective cohort study in 95 female soccer players

The aims of the study were to build models using logistic regression analysis of flexibility and strength tests to prospectively predict risk factors for anterior cruciate ligament tear (ACL-tear) in female soccer (FS) players, and to determine training cut-off for risk factors of the predictive model built. A prospective cohort study of 95 female players (aged 14-33 years) was conducted. Age, anthropometric data, soccer history, lower limb range of motion (ROM) and hip maximal isometric strength (MIS) were measured. At the prospective follow-up after 12 months, 7.4% of the players had developed an ACL-tear. The model showed a significant relationship (χ2(93) = 30.531, p < 0.001) between the ACL-tear and the predictor variables (leg length, HAD-NH [hip adduction] MIS, asymmetric ROM [ankle dorsiflexion with knee extended (AD-KE) and with knee flexed (AD-KF), and HE (hip extension)], hip ROM [HIR (internal rotation) and HAB (abduction)]). The Akaike Information Criteria (AIC) and Bayesian Information Criteria (BIC) for model fit were 30.24 and 51.79, respectively. The value R2 showed good model fit, 76.5% for Nagelkerke´s R2, 71.4% for McFadden´s R2 and 67.5% for Tjur´s R2. For the screening test, cut-off for leg length of ≥0.40 m, for HIR ROM of ≤44º and for asymmetry of HE ROM of ≥5° were set, which have an acceptable (AUC ≥ 0.755) discriminatory ability for the development of ACL-tear.

Description of ROM-SPORT I Battery: Keys to Assess Lower Limb Flexibility

Limited range of motion (ROM) is considered one of the most important intrinsic and modifiable risk factors for the most common sports-related injuries. In addition, controlling and monitoring an athlete's ROM is a strategy to achieve optimal ROM and improve athletic performance in sports, especially those that require high ROM in the major joints. Therefore, assessing ROM (pre-participation, during a rehabilitation process, on return to play, etc.) is important not only as a method to prevent sports injuries, but also as a quantitative determinant of the potential of athletic performance. However, despite the variety of different ROM assessment methods described in the literature, there is no consensus on which methods are best suited for this goal. Recently, the ROM-SPORT I battery has been shown to have advantages over other ROM assessment methods. This tool has not yet been fully described in detail for researchers, sports professionals, and clinicians to learn. The main objective of this study is to describe the ROM-SPORT I battery tests in detail using the following criteria: test description, simplicity of the test procedure, low need for human and material resources, predictive validity, and reliability.

Championship interseason period did not reduce knee peak moment: A 10-years retrospective study of 467 elite soccer players

Study aim: To compare knee moment profiles of professional soccer players from different playing positions before and after an interseason period.

Material and methods: Retrospective study of 467 healthy, professional elite Brazilian soccer players before and after an official championship interseason period during 10-years. Main outcome measures were isokinetic peak moment from knee extensors and flexors from concentric and eccentric contractions. A Two-way ANOVA analysis was used to compare each playing position before and after interseason period.

Results: It was found no statistical difference in Ext.CPT (from p = 0.11 to p = 0.97), Ext.EPT (from p = 0.07 to p = 0.85), Flx. CPT (from p = 0.14 to p = 0.90) or Flx.EPT (from p = 0.10 to p = 0.91) between End-Season and Pre-Season evaluations for all playing positions (from Goalkeepers, Defenders, Backsiders, Midfielders and Forwards).

Conclusions: Isokinetic peak moment did not have significant differences after an interseason period of 4 to 6 weeks, allowing trainers and coaches to focus their pre-season period on other performance concerns than strengthening.

Lower Extremity Flexibility Profile in Basketball Players: Gender Differences and Injury Risk Identification

Analysis of the flexibility profile of basketball players (BPs) can reveal differences in range of motion (ROM) by gender and also identify those players who are at higher risk for sports injuries. A descriptive observational study was conducted to determine the lower extremity flexibility profile of sixty-four basketball players and gender differences to identify players at higher risk of injury due to limited and asymmetric ROM in one or more movements. Participants: Sixty-four (33 male and 31 female) competitive athletes from the national leagues of the Spanish basketball league system participated in the present study (power of sample size ≥0.99). The eight passive ROM tests of the hip, knee and ankle were assessed using the ROM-SPORT battery. Each player completed a questionnaire on age, basic anthropometric data, dominant extremities, and training and sport-related variables. The lower extremity flexibility profile was established at 15° and 10° hip extension (HE), 39° and 38° ankle dorsiflexion with knee extended (ADF-KE), 40° and 39° ankle dorsiflexion with knee flexed (ADF-KF), 43° and 43° hip abduction (HAB), 75° and 61° hip abduction with the hip flexed (HAB-HF), 78° and 83° hip flexion with the knee extended (HF-KE), 134° and 120° knee flexion (KF), and 145° and 144° hip flexion (HF) by male and female basketball players, respectively. Sex differences in HE, HAB-HF, and KF were observed in BPs (p ≤ 0.01; Hedges’ g ≥ 1.04). Players reported limited ROM in ADF-KF, HE, HAB-HF, HF-KE, and KF; and asymmetric ROM mainly in HE, ADF-KE, KF, ADF-KF, and HF-KE. In conclusion, this study provides gender-specific lower extremity flexibility profile scores in BPs that can help athletic trainers and athletic and conditioning trainers to identify those players who are at higher risk of injury due to abnormal ROM scores.

Assessment of the Range of Movement of the Lower Limb in Sport: Advantages of the ROM-SPORT I Battery

Range of movement (ROM) assessment is an important strategy to increase physical-technical performance and minimize the risk of sports-related injuries. Currently, there is no consensus regarding which ROM assessment method is the most appropriate. The main objective of this study was to perform a systematic review of the test batteries available for the assessment of lower limb ROM; additionally, we compare the ROM-SPORT I battery with those previously reported in the literature. The systematic review was conducted following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. The identification of publications was made by using the databases SciELO, Medline, Scopus, PubMed, and Web of Science. Based on the inclusion criteria, sixteen publications were selected and analyzed. The ROM-SPORT I battery is the most valid of the analyzed methods. This battery evaluates the ROM of eleven lower limb movements. The inclinometer with a telescopic arm and a box is a simpler, more comfortable, and faster procedure than others. The Lumbosant support and use of two examiners are essential to avoid compensatory movements to obtain reliable measurements during ROM assessment. The ROM-SPORT I is a field-based battery of tests that may be used by sports professionals, clinics, and researchers in applied settings to accurately assess and monitor lower extremity ROM.

External and Total Hip Rotation Ranges of Motion Predispose to Low Back Pain in Elite Spanish Inline Hockey Players

Low back pain (LBP) is a common ailment in competitive athletes. Although the association between limited range of motion (ROM) and prevalence of LBP has been widely investigated in other sports, there is no research about this topic in inline hockey (IH). The main purposes of this study in IH players were (1) to analyze the association between hip ROM and LBP and (2) to establish a diagnostic cutoff for ROM of high risk of LBP. Twenty elite IH players from the two Spanish National Teams (male and female) were assessed for passive maximum hip ROMs; the movement evaluated were the hip external [HER] and internal [HIR] rotation, hip flexion with flexed [HF-KF] and extended [HF-KE] knee, hip adduction with flexed hip [HAD-HF], hip abduction with neutral [HAB] and flexed [HAB-HF] hip, and hip extension [HE]. LBP was retrospectively monitored for the last 12 months before the date of ROM assessment by using a questionnaire. The data were analyzed via a binary logistic regression and receiver operating characteristic curves. The 70% of players had developed LBP during the retrospective study period. Significant differences between LBP group and asymptomatic group for HER (p = 0.013, d [Cohen’s effect size] = 1.17) and hip total rotation [HTR] (p = 0.032, d [Cohen’s effect size] = 1.05) were observed. The cutoff points with the greatest discriminatory capacity were 56.5° for HER and 93° for HTR ROMs.

Flexibility in Spanish Elite Inline Hockey Players: Profile, Sex, Tightness and Asymmetry

Limited ranges of motion (ROM) have been considered as a relevant risk factor for team sports injuries. The main purposes of the current study were to describe the lower extremity ROM profile, muscular tightness and asymmetries in elite inline hockey players and to examine sex-related differences. Twenty professional inline hockey players from 2 Spanish National Teams (male and female) were measured of passive hip extension [HE], hip adduction with hip flexed 90° [HAD-HF], hip flexion with the knee flexed [HF-KF] and extended [HF-KE], hip abduction with the hip neutral [HAB] and hip flexed 90° [HAB-HF], hip external [HER] and internal [HIR] rotation, knee flexion [KF], ankle dorsiflexion with the knee flexed [ADF-KF] and extended [ADF-KE] ROMs of the dominant and non-dominant leg ROMs were taken. A paired t-test was carried out to assess asymmetries. ROM values were classified as “normal versus tightness”, and “normal versus asymmetry” according to the proposed reference values. The effect size for each variable was analyzed. Male team exhibited asymmetry in HF-KF (133.2° dominant vs. 129.8° non-dominant; p = 0.042; d = 0.7243 [moderate effect sizes]) and female team in ADF-KF (38.8° dominant vs. 41.0 non-dominant; p = 0.001; d = 0.6 [moderate effect sizes]) and HAB ROM (41.2° dominant vs. 38.8 non-dominant; p = 0.005; d = 1.1767 [moderate effect sizes]). Male players reported asymmetry in HAD-HF (n = 5), HER (n = 4) and HE (n = 3), whereas female players presented asymmetries in HER (n = 4), HE (n = 3) and KF (n = 2). Overall, 20–100% of all participants showed limited KF, HF_KE, HIR, HE, ADF_KF, HAD-HF, HF-KF, ADF_KE, HTR and HER ROM. The results of this study reinforce the requirement of prescribing exercises aimed at improving hip, knee and ankle ROM within everyday inline hockey practices. In addition, as some asymmetries were found, unilateral flexibility training should be considered where appropriate.

Age-related differences in flexibility in soccer players 8-19 years old

BACKGROUND

Muscle flexibility is a main component of health-related fitness and one of the basic components of fitness for the performance in some sports. Sport and health professionals require the flexibility profile of soccer to define quantitative aims in the training of flexibility. The aim of this study was to identify age-related differences in lower extremity flexibility in youth soccer players.

METHODS

Seventy-two young male soccer players (age: 13.0 ± 3.1 y; body mass: 50.5 ± 15.3 kg; stature 158.2 ± 16.8 cm; BMI: 19.6 ± 2.6 kg/m2) completed this study. Measures of eleven passive hip (hip extension (HE), hip adduction with hip flexed 90°(HAD-HF90°), hip flexion with knee flexed (HF-KF) and extended (HF-KE), hip abduction with hip neutral (HAB) and hip flexed 90°(HAB-HF90°), hip external (HER) and internal (HIR) rotation), knee (knee flexion (KF)) and ankle dorsiflexion (ankle dorsiflexion with knee flexed (ADF-KF) and extended (ADF-KE)) ranges of motion (ROM) were taken. Descriptive statistics were calculated for hip, knee and ankle ROM measured separately by leg (dominant and non-dominant) and age-group (U10, U12, U14, U16 and U19). The data was analysed using a one-way analysis of variance (ANOVA) to examine the interaction of 11 ROM in the different players' age-group.

RESULTS

Generally, U10 and/or U12 soccer players obtain the highest mean value in almost all ROM evaluated (U10: HAD-HF [39.6° ± 4.3°], ADF-KE [32.3° ± 4.1°], HER [63.5° ± 5.6°] and HAB-HF90°[64.1° ± 7.5°]; U12: HE [17.7° ± 6.2°], HAB [35.6° ± 3.0], HIR [60.8° ± 4.7°] and KF [133.8° ± 7.1°]). Nonetheless, significant differences between the players' age-groups are just found in HAD-HF90°(p = .042; ES = .136), HAB (p = .001; ES = .252), HIR (p = .001; ES = .251), HER (p < .001; ES = .321) and HAB-HF90°(p < .001; ES = .376) ROM, showing a progressive and irregular decrease in these ROM until the U19 team.

CONCLUSION

The findings of this study reinforce the necessity of prescribing exercises aimed at improving HAD-HF90°  ROM in U16, HAB ROM in U14, HIR ROM in U16 and U19, HER ROM in U12 and U19, and HAB-HF90°  ROM in U16 and U19 players within everyday soccer training routines.

Examination of Physical Characteristics and Positional Differences in Professional Soccer Players in Qatar

Physical characteristics in professional soccer differ between competition levels and playing positions, and normative data aid practitioners in profiling their players to optimize performance and reduce injury risk. Given the paucity of research in Arabic soccer populations, the purpose of this study was to provide position-specific normative values for professional players competing in the Qatar Stars League. One hundred and ninety-five players completed a musculoskeletal assessment as part of an annual periodic health examination. Tests included measures of range of motion (hip, ankle, and hamstring), bilateral and unilateral jump performance, and quadriceps/hamstring (isokinetic/NordBord), hip adduction/abduction (eccentric), and groin (isometric) strength. Descriptive data were examined, and positional differences were analyzed using a one-way analysis of variance (ANOVA). Goalkeepers were significantly heavier (p < 0.01), had a higher body mass index (p < 0.05) than outfield positions and demonstrated greater absolute strength. Defenders were the strongest relative to body mass, and these differences were significant (p < 0.05) versus goalkeepers and strikers. No meaningful between-group comparisons were apparent for jumping or range of motion tests. Compared to mean values from other professional leagues, soccer players in Qatar appear to be shorter, lighter and display inferior strength and jump capacities. These data can be used to tailor training and rehabilitation programs to the specifics of the league and position in which the athletes compete.

Comprehensive profile of hip, knee and ankle ranges of motion in professional football players

BACKGROUND

Limited ranges of motion (ROM) have been considered as a primary risk factor for some football injuries, but only a few studies have analyzed differences in lower extremity joints. The main purposes were: 1) to describe the lower extremity ROM profile in professional football players; and 2) to examine differences between goalkeepers and outfield players.

METHODS

Eighty-two professional male football players from 4 teams were measured in the 2013 pre-season. Measures of passive hip (flexion with knee flexed [PHFKF] and extended [PHFKE], extension [PHE], abduction [PHA], external [PHER] and internal [PHIR] rotation), knee (flexion [PKF]) and ankle (dorsiflexion with knee flexed [ADFKF] and extended [ADFKE]) ROMs were taken. Magnitude-based inferences exploring differences between player position and limb were made.

RESULTS

Overall, 46% of all participants showed restricted PHFKE and/or around 30% showed restricted ADFKF ROM values. Contrarily, most players reported normal PHFKF, PHE, PHIR and PHER as well as PKF ROM scores with percentage values close to 100%. Bilateral meaningful differences for PHA, PHIR and PHER were found in approximately 30% of outfield players and goalkeepers. Statistical analysis found trivial differences between players for PHFKE, PHE, PHIR, PHER, ADFKE and ADFKF. However, moderate differences between players were found for PHFKF, PHA and PKF, with goalkeepers demonstrating higher values than outfield players.

CONCLUSIONS

The findings of this study reinforce the necessity of prescribing exercises aimed at improving PHFKE and ADFKF ROM within everyday football training routines. In addition, as some bilateral deficits were observed, unilateral training should be considered where appropriate.

The isokinetic strength profile of elite soccer players according to playing position

The aim of this study was to compare isokinetic strength performance profiles in elite soccer players across different field positions. A total of 111 elite international players of Polish Ekstraklasa (the top division in Poland) were examined during the 2010–2015 seasons. The players were classified into six positional roles: central defenders (CD), external defenders (ED), central midfielders (CM), external midfielders (EM), forwards (F), and goalkeepers (G). The concentric isokinetic strength (peak torque [PT] of quadriceps and hamstrings, H/Q ratios) was calculated for the dominant leg and the non-dominant leg at angular velocity of 1.05 rad ·s^–1, whereas to assess isokinetic muscle endurance, the total work [TW] at angular velocity of 4.19 rad ·s^–1, was taken into consideration. The results showed that isokinetic strength performance varies significantly among players in different playing positions. The analysis of PT for quadriceps (PT-Q) and hamstrings (PT-H) generally showed that the goalkeepers and central midfielders had lower strength levels compared to other playing positions. In the case of PT-H and hamstring/quadricep (H/Q) peak torque ratios, statistically significant differences were also noted for the legs, where mean values noted for the dominant leg were higher than for the non-dominant leg. For TW for quadriceps (TW-Q) and hamstrings (TW-H), statistically significant differences were noted only between playing positions. TW-Q values for goalkeepers were lower than for central defenders and external midfielders. TW-H values for goalkeepers were lower than for central midfielders, central defenders and external midfielders. This study showed that specific functional activity of players in individual positions on the field influences the varied profile of isokinetic strength performance.

Lower-extremity strength ratios of professional soccer players according to field position

Previous investigators have proposed that knee strength, hamstrings to quadriceps, and side-to-side asymmetries may vary according to soccer field positions. However, different results have been found in these variables, and a generalization of this topic could lead to data misinterpretation by coaches and soccer clubs. Thus, the aim of this study was to measure knee strength and asymmetry in soccer players across different field positions. One hundred and two male professional soccer players performed maximal concentric and eccentric isokinetic knee actions on the preferred and nonpreferred legs at a velocity of 60° · s. Players were divided into their field positions for analysis: goalkeepers, side backs, central backs, central defender midfielders, central attacking midfielders, and forwards. Results demonstrated that only goalkeepers (GK) differed from most other field positions on players' characteristics, and concentric peak torque across muscles. Although all players presented functional ratios of the preferred (0.79 ± 0.14) and nonpreferred (0.75 ± 0.13) legs below accepted normative values, there were no differences between positions for conventional or functional strength ratios or side-to-side asymmetry. The same comparisons were made only between field players, without inclusion of the GK, and no differences were found between positions. Therefore, the hamstrings to quadriceps and side-to-side asymmetries found here may reflect knee strength functional balance required for soccer skills performance and game demands across field positions. These results also suggest that isokinetic strength profiles should be considered differently in GK compared with other field positions due to their specific physiological and training characteristics.

Physical Characteristics, Physiological Attributes, and On-Field Performances of Soccer Goalkeepers

The soccer goalkeeper (GK) is required to perform strenuous actions during practice sessions and actual games. One of the objectives of those professionals who work with GKs is to obtain relevant information on physical characteristics and physiological attributes of GKs, and to use it effectively when planning training programs for them. This article has three purposes: (a) to review a series of studies (n = 23) on physical characteristics, physiological attributes, and on-field performances of soccer GKs; (b) to outline a number of methodological limitations and research concerns associated with these studies; and (c) to suggest several practical recommendations for soccer coaches who work with GKs. Four main fndings emerged from our review: (a) professional adult GKs usually are over 180 cm tall and have a body mass of over 77 kg; (b) studies on agility and speed produced mixed results, with some showing similar values between GKs and field players and others showing reduced performance in GKs; (c) GKs usually have higher vertical jump values when compared with players playing the various field positions; (d) GKs cover approximately 5.5 km during a game, mostly by walking and jogging. Four methodological limitations and research concerns associated with the reviewed studies were discussed, among them the lack of a longitudinal approach and the lack of on-field performance studies. Three practical recommendations are made for coaches, one of which is that coaches should adopt a careful approach when selecting testing protocols and devices for the assessment of GKs’ physiological attributes.

Testing soccer players

To cope with the physiological demands of soccer, players must be competent across several fitness components. The use of fitness tests in the laboratory and field assist in examining soccer players' capabilities for performance both at the amateur and elite levels. Laboratory tests provide a useful indication of players' general fitness. Accurate test results can be obtained with the use of a thorough methodology and reliable equipment. Laboratory tests are used sparingly during the season because of the time-consuming nature of the tests. Instead, tests are generally carried out at the start and end of the pre-season period to evaluate the effectiveness of specific training interventions. Field tests provide results that are specific to the sport and are therefore more valid than laboratory tests. The reduced cost, use of minimal equipment and the ease with which tests can be conducted make them more convenient for extensive use throughout the season. Although data from laboratory and field tests provide a good indication of general and soccer-specific fitness, individual test results cannot be used to predict performance in match-play conclusively because of the complex nature of performance in competition. Fitness tests in conjunction with physiological data should be used for monitoring changes in players' fitness and for guiding their training prescription.

Maturity-associated variation in sport-specific skills of youth soccer players aged 13 – 15 years

The aim of this study was to estimate the contribution of experience, body size and maturity status to variation in sport-specific skills of adolescent soccer players. The participants were 69 players aged 13.2-15.1 years from three clubs that competed in the highest division for their age group. Height and body mass were measured and stage of pubic hair development was assessed at clinical examination. Years of experience in football was obtained at interview. Six football skill tests were administered: ball control with the body, ball control with the head, dribbling with a pass, dribbling speed, shooting accuracy and passing accuracy. Multiple linear regression analysis was used to estimate the relative contributions of age, stage of sexual maturity, height, body mass and years of formal training in soccer to the six skill tests. Age, experience, body size and stage of puberty contributed significantly but in different combinations to the variance in four of the six skill tests: dribbling with a pass (21%; age, stage of maturity), ball control with the head (14%; stage of maturity, height, body height x body mass interaction), ball control with the body (13%; stage of maturity, years of training) and shooting accuracy (8%; stage of maturity, height; borderline significance, P = 0.06). There were no significant predictors for the tests of dribbling speed and passing accuracy. In conclusion, age, experience, body size and stage of puberty contributed relatively little to variation in performance in four of the six soccer-specific skill tests in adolescent footballers aged 13-15 years.

Biomechanics of the first ray part V: The effect of equinus deformity. A 3-dimensional kinematic study on a cadaver model

The positional change of the medial column of the foot in closed kinetic chain with variable Achilles tendon tension was investigated in seven fresh frozen cadaver specimens using a 3-dimensional radio wave tracking system. The distal tibia and fibula and the intact ankle and foot and were mounted on a non-metallic loading frame. The frame allowed positioning of the foot to simulate midstance phase of gait while the tibia and fibula were axially loaded to 400 N. To record osseous motion, receiving transducers were attached to the first metatarsal, medial cuneiform, navicular, and talus. Movements of these bones in 3-dimensional space were measured as specimens were axially loaded and midstance motor function was simulated using pneumatic actuators. To simulate a progressive equinus influence, force was applied to the Achilles tendon at tensile loads of 0%, 30%, and 60% of predicted maximum strength during each test trial. Osseous positions and orientations were collected and analyzed in all three cardinal planes utilizing data recorded. As Achilles load increased, the position of the first metatarsal became significantly more inverted ( P < .05). Although not statistically significant, remarkable trends of arch flattening motion were detected in the distal segments of the medial column with varied Achilles load. Increased Achilles load reduced the influence of peroneus longus on the medial column.

A survey of flexibility training protocols and hamstring strains in professional football clubs in England

OBJECTIVES

To investigate the relation between current flexibility training protocols, including stretching, and hamstring strain rates (HSRs) in English professional football clubs.

METHOD

Questionnaire based data on flexibility training methods and HSRs were collected from 30 English professional football clubs in the four divisions during the 1998/99 season. Data were coded and analysed using cross tabulation, correlation, and multiple regression.

RESULTS

Flexibility training protocols were characterised by wide variability, with static stretching the most popular stretching technique used. Hamstring strains represented 11% of all injuries and one third of all muscle strains. About 14% of hamstring strains were reinjuries. HSRs were highest in the Premiership (13.3 (9.4)/1000 hours) with the lowest rates in Division 2 (7.8 (2.9)/1000 hours); values are mean (SD). Most (97%) hamstring strains were grade I and II, two thirds of which occurred late during training/matches. Forwards were injured most often. Use of the standard stretching protocol (SSP) was the only factor significantly related to HSR (r = -0.45, p = 0.031) in the correlation analysis, suggesting that the more SSP is used, the lower the HSR. About 80% of HSR variability was accounted for by stretching holding time (SHT), SSP, and stretching technique (STE) in the multiple regression equation: HSR = 37.79 - (0.33SHT + [corrected] 10.05SSP + 2.24STE) +/- 2.34. SHT (negatively correlated with HSR) was the single highest predictor, and accounted for 30% of HSR variability, and an additional 40% in combination with SSP.

CONCLUSIONS

Flexibility training protocols in the professional clubs were variable and appeared to depend on staffing expertise. Hamstring stretching was the most important training factor associated with HSR. The use of SSP, STE, and SHT are probably involved in a complex synergism which may reduce hamstring strains. Modification of current training patterns, especially stretching protocols, may reduce HSRs in professional footballers.

Physical fitness, injuries, and team performance in soccer

PURPOSE

To investigate the relationship between physical fitness and team success in soccer, and to test for differences in physical fitness between different player positions.

METHODS

Participants were 306 male soccer players from 17 teams in the two highest divisions in Iceland. Just before the start of the 1999 soccer season, the following variables were tested: height and weight, body composition, flexibility, leg extension power, jump height, and peak O2 uptake. Injuries and player participation in matches and training were recorded through the 4-month competitive season. Team average physical fitness was compared with team success (final league standing) using a linear regression model. Physical fitness was also compared between players in different playing positions.

RESULTS

A significant relationship was found between team average jump height (countermovement jump and standing jump) and team success (P = 0.009 and P = 0.012, respectively). The same trend was also found for leg extension power (P = 0.097), body composition (% body fat, P = 0.07), and the total number of injury days per team (P = 0.09). Goalkeepers demonstrated different fitness characteristics from outfield players. They were taller and heavier, more flexible in hip extension and knee flexion, and had higher leg extension power and a lower peak O2 uptake. However, only minor differences were observed between defenders, midfield players, and attackers.

CONCLUSION

Coaches and medical support teams should pay more attention to jump and power training, as well as preventive measures and adequate rehabilitation of previous injuries to increase team success.

Effects of age on the reciprocal peak torque ratios during knee muscle contractions in elite soccer players

To investigate the effects of age on the reciprocal peak torque ratios during knee muscle contractions, 25 elite male soccer players, aged 22.3 +/- 3.8 yr (18-28), volunteered for the present study. The players were grouped as adult (> 21 years, n = 13) and young players (< or = 21 years, n = 12). Maximal concentric (CON) and eccentric (ECC) isokinetic thigh muscle strength was measured at angular velocities of 30 degrees, 180 degrees, 240 degrees and 300 degrees/s. ECC and CON peak torques of knee flexors (hamstring, HAM) and CON peak torques of knee extensors (quadriceps, QUA) in the dominant knee were greater (P < 0.05) in adult players than in young players at 180, 240 and 300 degrees/s. ECC HAM/CON QUA peak torque ratio at 300 degrees/s was greater (P < 0.05) for adult players compared to young players in the dominant knee but not in the nondominant knee. Furthermore, conventional HAM/QUA peak torque ratios of the dominant knee at all angular velocities for ECC contraction were higher (P < 0.05) in adult players than in young players. In conclusion, the findings of the present study indicate that the reciprocal torque ratio is influenced by age in the dominant knee of elite soccer players. Because there was no effect of age for the nondominant leg, the findings of the present study are more likely to be the result of the training background of the players than their age.

Dynamic strength of the quadriceps muscle and sports activity

The study objectives were to examine the dynamic strength of the quadriceps muscle in athletes, and investigate its association with participation in sport. The study comprised 168 active competitive non-pregnant athletes, aged 14-24 years. The dynamic strength of their quadriceps muscle was measured, and they answered a questionnaire about sports activity and occupation. The dynamic strength of the quadriceps muscle was significantly higher in men than in women, and was positively associated with body weight, years of jogging, years of soccer, and weekly hours of basketball. In conclusion, the dynamic strength of the quadriceps muscle seems to be associated with sports activity. The results suggest sport specific adaptation, which may reflect high levels of running and jumping activity.

Flexibility and its effects on sports injury and performance

Flexibility measures can be static [end of ROM (range of motion)], dynamic-passive (stiffness/compliance) or dynamic-active (muscle contracted, stiffness/compliance). Dynamic measures of flexibility are less dependent on patient discomfort and are more objective. Acute and chronic changes in flexibility are likely to occur with stretching exercises, but it is difficult to distinguish between changes in stretch tolerance as opposed to changes in muscle stiffness. How flexibility is measured impacts these findings. There is no scientifically based prescription for flexibility training and no conclusive statements can be made about the relationship of flexibility to athletic injury. The literature reports opposing findings from different samples, frequently does not distinguish between strain, sprain and overuse injury, and rarely uses the proper denominator of exposure. There is basic scientific evidence to suggest that active warm-up may be protective against muscle strain injury but clinical research is equivocal on this point. Typically, specific flexibility patterns are associated with specific sports and even positions within sports. The relationship of flexibility to athletic performance is likely to be sport-dependent. Decreased flexibility has been associated with increased in-line running and walking economy. Increased stiffness may be associated with increased isometric and concentric force generation, and muscle energy storage may be best manifested by closely matching muscle stiffness to the frequency of movement in stretch-shorten type contractions.

Time-of-day dependence of isokinetic leg strength and associated interday variability

The purpose of this study was to assess the interday variability and time-of-day effects on selected isokinetic leg strength indices. Nine adult collegiate sportsmen (mean(s.e.) age 19.6(0.5) years; mean(s.e.) height 1.81(0.02) m; mean(s.e.) body mass 76.5(3.1) kg) completed a series of nine test sessions, organized so that each subject was tested three times within a day (08.00-09.00 hours; 13.00-14.00 hours; 18.00-19.30 hours), on three occasions, each separated by a minimum of 7 days. Gravity-corrected indices of extension peak torque (EPT), flexion peak torque (FPT), and the peak torque ratio (PTR), at contraction velocities of 1.05 rad s-1 and 3.14 rad s-1, were calculated for each subject using an isokinetic dynamometer. Two-way repeated measures analysis of variance of coefficient of variation (V%) scores revealed no significant differences in performance variability across within-subject factors of time-of-day and performance index (P > 0.05). Overall mean(s.e.) V% for scores across experimental conditions were 3.97(0.72)% at 1.05 rad s-1 and 5.98(1.23)% at 3.14 rad s-1, suggesting that similar levels of measurement error occur between 08.00-19.30 hours. One-way repeated measures analysis of variance of absolute strength indices (EPT, FPT and PTR) revealed that significantly higher scores were achieved during session 3 (18.00-19.30 hours), with mean(s.e.) values of 249.1(40.0) N m, 149.0(32.3) N m, 59.5(5.0)% at 1.05 rad s-1, and 172.1(38.7) N m, 121.3(27.7) N m, 71.1(6.2)% at 3.14 rad s-1, respectively (P < 0.05). This finding appears to be consistent with current knowledge about time-of-day effects on the assessment of muscular strength. Thus for stable and maximal values to be obtained during isokinetic leg testing, the use of multiple-trial protocols is recommended, with testing occurring as close to 18.00-19.30 hours as possible. In addition, the observed significant time-of-day effect suggests that appropriate comparison of maximal isokinetic leg strength can only be achieved based on data obtained within 30 min of the same time of day.

Applied physiology of female soccer players

Women's soccer is in its infancy as a sport and research into its physiological demands and the physical characteristics of players is somewhat limited. There is now an increasing demand for scientific investigation of the female game and of the players, match analysis and role variations requiring particular attention. Current research suggests that the demands of the game for women are similar to those placed on male players. Women are reported to cover a similar distance (mean 8471m) to their male counterparts during a game and much the same proportions of the game appear to be devoted to exercise of varying intensities. Furthermore, female and male players appear to tax the aerobic and anaerobic energy systems to a similar level. The physical and physiological characteristics of female soccer players are comparable with those of other female games players and are more favourable than average for the population. Mean body fat percentages of between 19.7 and 22.0% and VO2max values of between 47.1 and 57.6 ml/kg/min have been reported for elite female players, while faster than average sprint times are also characteristic of them.

Physiological profiles of Hong Kong élite soccer players

Most physiological profiles of élite soccer players originate from Western Europe and North America. Unfortunately, there is a scarcity of descriptive data on the physical characteristics of Asian soccer players. Therefore, the purpose of this study was to evaluate the physiological profiles of élite soccer players in Hong Kong. It was conducted in conjunction with the selection of the Hong Kong team before the 1990 Beijing Asian Games. In all, 24 professional soccer players were selected from a pool of 180 players as subjects for the study. The following means(s.d.) were observed: height 173.4(4.6) cm; weight 67.7(5.0) kg; body fat 7.3(3.0)%; forced vital capacity (FVC) 5.1(0.6) l; maximum oxygen uptake (VO2max) 59.1(4.9) ml kg-1 min-1; anaerobic threshold (AT 80.0(7.2)% of VO2max; alactic power index 13.5(2.4) W kg-1; lactic work index 298(27) J kg-1; peak isokinetic dominant knee extensor and flexor strengths 2.72(0.36) Nm kg-1 and 1.65(0.20) Nm kg-1. On average the physique of Hong Kong soccer players appeared to be smaller and lighter than those found in Europe, which may be one of the key factors that contribute to the lack of success of Hong Kong soccer teams in international competition.

Specific muscular development in under-18 soccer players

A comparison of the under-18 (U-18) and under-16 (U-16) squads of the Canadian national soccer team with a representative sample of Canadians (Canada Fitness Survey, 1983) showed a tendency for the development or selection of the older players in teams of stature (U-18, 175.8 cm; U-16, 171.1 cm; CFS, 170.9 cm) and lean body mass (U-18, 63.4; U-16, 57.9; CFS, 54.2 kg). The larger lean mass of the older players could not be explained simply by size. The U-18s also showed greater isokinetic leg extension force (particularly for rapid movements) and explosive strength (vertical jump) relative to the younger players, although the knee extension force was less than in some classes of athlete. Part of the gain in mass seems due to local training of the hip and leg muscles and part to a more general muscular development. Contrary to some reports, the hip flexibility of the Canadian players (sit and reach test) was greater than for a national sample; this may be important in avoiding soft tissue injuries to the legs. However, aerobic power (58.3 +/- 5.3 ml kg-1 min-1) and body fat (8.0 +/- 1.1%) were unremarkable.

Lower Extremity Strength and Active Range of Motion in College Baseball Pitchers: A Comparison between Stance Leg and Kick Leg

The role of the lower extremities and torso is vital in the pitching mechanism. However, a review of the literature reveals information primarily dealing with the upper extremity's role in throwing. This pilot study was conducted to: 1) determine selected lower extremity strength and range of motion measurements in sixteen college baseball pitchers, and 2) compare measurements in the stance leg to the kick leg. When preseason profiling is not possible, clinical norms for those treating college pitchers can be valuable in proper rehabilitation of the lower extremity. Also, by determining trends in lower extremity strength and motion when comparing kick (plant) leg to stance (drive) leg, a better understanding of lower extremity kinematics in the pitching act can be appreciated. Statistically significant differences were found in the active range of motion in plantarflexion, hip internal rotation, and hip extension of the stance leg, as well as hip flexion of the kick leg. lsokinetic evaluations at slow and fast speeds revealed significant differences in the strength of ankle dorsiflexors and hip flexors at slow speeds of the kick leg. Strength of the hamstrings on the kick leg was significant at fast speeds as was strength of the hip external rotators on the stance leg. J Orthop Sports Phys Ther 1986;8(1):10-14.

The Applied Sport Science of Soccer

In brief: Participation in soccer is increasing, possibly because many people believe that anyone can play the game. This article reviews the nature and demands of soccer and the physiological characteristics of the players, including aerobic power, anaerobic power, muscle strength, flexibility, agility, glycogen use, and fiber types. Soccer players must perform short sprints as well as cover long distances during a game. Soccer players fall in the middle of the ranges for athletes in all of the measured variables. The author concludes that soccer players are unique in their ability to repeatedly perform difficult motor skills during constantly changing tactical situations.