Yo-Yo Intermittent Recovery Test Level Research Articles

The NIE Intermittent High-Intensity Running Test: A Reliable and Valid Test for Assessment of Soccer-Specific Fitness

The overall activity pattern of soccer is that of intermittent high-intensity (Int-HINT) type and elite players have a greater repeated high-intensity running capability. Since soccer involves rapidly changing work intensities in an unpredictable manner, tests simulating overall activity pattern in a cyclical sequence have limited practical usefulness in testing of soccer fitness. The primary aim of this study was to develop a laboratory-based protocol to specifically assess the Int-HINT running capability in soccer players. University team games athletes (n=8, Mean ± SD; age 22.30 ± 1.65 years, stature 1.73 ± 0.04 m, body mass 69.36 ± 6.04 kg) participated in the reliability study and male youth professional soccer players (n=20, Mean ± SD age, 17.5 ± 0.3 yrs; stature, 1.73 ± 0.04 m; body mass, 67.2 ± 7.5 kg) participated in the validity study. The players performed on the NIE Intermittent High-intensity (NIE Int-HINT) Running Test during the preseason, early in-season and end mid-season phases of the soccer season. Performance was measured as total distance covered on the treadmill. The participants also performed the YoYo Intermittent Recovery Test Level 2 (YoYo IRT L2) during each phase of the competition season. The NIE Int-HINT test was found to be of high reliability (ICC, 0.98; CV, 2.1%; ratio limits of agreement (rLOA) 0.99 ×/÷ 1.03). A positive and significant correlation (p< 0.05) was found between the performance in the NIE Int-HINT test and the YoYo IRT L2 performance (r = 0.68-0.77) during different phases of the soccer season. The NIE Int-HINT test provided a reliable measure of intermittent high-intensity running capability and a valid and sensitive method of estimating soccer-specific fitness in youth professional soccer players. Further studies are needed to evaluate the applicability of this test in adult elite soccer players and other intermittent team game athletes.

A Comparison of Heart Rate Response and Frequencies of Technical Actions Between Half-Court and Full-Court 3-A-Side Games in High School Female Basketball Players

The purpose of this study was to compare heart rate (HR) response and frequency of technical actions between half-court and full-court 3-a-side games in female high school basketball players. Twelve young female basketball players (age 15.5 ± 0.5 years; height 165.1 ± 5.7 cm; body mass 57.3 ± 7.2 kg; training age 4.2 ± 0.7 years; HRmax 202.9 ± 5.6 b·min(-1)) participated in this study voluntarily. On the first day, anthropometric measurements (height and body mass) were taken for each player; this was followed by the Yo-Yo intermittent recovery test (YIRT) level 1 for the subjects. Then, half-court and full-court 3-a-side games were organized in random order at 2-day intervals. The HRmax for each player was determined during the YIRT, after which the HR was measured during the 3-a-side games. In addition, the frequencies of different categories of technical actions were counted manually during the 3-a-side games. A paired t-test was calculated for each dependent variable, including HR, percentage of maximum HR (%HRmax), and the frequencies of different technical actions to compare half-court and full-court 3-a-side games. The study results indicate that the full-court 3-a-side games produced significantly higher responses than the half-court 3-a-side games in terms of HR and %HRmax (p < 0.05), whereas the half-court games resulted in significantly higher frequencies of technical actions (p < 0.05). The results of this study suggest that, if coaches want to achieve greater HR responses, coaches of female high school basketball players should organize full-court 3-a-side games, whereas coaches who want to focus on technical actions should arrange half-court 3-a-side games.

The Yo-Yo intermittent recovery test level 1 as a high intensity training tool: Aerobic and anaerobic responses

ObjectiveThe aim of this study was to investigate the effects of using the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) as a high intensity training tool for sedentary university female students. MethodsBaseline measures were recorded for body fat percentage, Wingate Anaerobic Test (WAnT) peak power and mean power, and Yo-Yo IR1 performance. Subjects were matched in pairs for body fat percentage and then randomly allocated to the intervention group (INT) (n=12) or control group (CON) (n=13). The INT undertook a 6-week training programme twice a week using the Yo-Yo IR1. The CON undertook no training. ResultsThe INT increased their Yo-Yo IR1 performance (230±38m baseline vs 403±152m post-training), WAnT peak power (970±176Watts baseline vs 1148±159Watts post-training), and WAnT mean power (399±55Watts baseline vs 439±53 Watts post-training) (p<0.05). No changes were observed in the CON (p>0.05). ConclusionThe results of this study show that a 6-week high intensity intermittent training programme using the Yo-Yo IR1 as a training intervention increases both aerobic and anaerobic capacity in a sedentary female population.

The Relationship Between the Yo-Yo Tests, Anaerobic Performance and Aerobic Performance in Young Soccer Players

The purposes of this study were to determine the relationship between performance in the Yo-Yo intermittent recovery test level 1 (YIRT1), the Yo-Yo intermittent recovery test level 2 (YIRT2) and the Yo-Yo endurance test (continuous) (YET) with maximal oxygen uptake (VO2max) and Wingate anaerobic performance (WaNT) test results in young soccer players (age 15.00 ± 0.0 years, body height 176.3 ± 4.2 cm and body mass 68.1 ± 3.6 kg). An ergospirometry device was used during the treadmill test (TRT) to determine VO2max. At the end of the study, significant differences were found between the Yo-Yo tests and TRT in terms of HRmax (TRT = 195,92, YIRT1 = 197,83, YIRT2 = 198,5 YET = 198) (p > 0.05). While there were moderate correlations between VO2max and YIRT 1–2 performances (respectively, r = 0.56, r = 0.53), there was only a weak relationship between VO2max and YET performance (r = 0.43) (distance covered). There were also moderate significant negative correlations between performance in the YIRT2 and peak power measured in the WaNT (r = −0.55), although there were no significant correlations between performance in the three tests and average power. A moderate negative correlation was found between performance in the YIRT2 and Fatigue index (FI) (r = −0,66). In conclusion, the YIRT2 may be a more suitable field test for determining both aerobic and anaerobic performance in soccer players.

Effects of a soccer season on anthropometric characteristics and physical fitness in elite young soccer players

The aim of this study was to evaluate the effect of a soccer-training season on the anthropometric and performance characteristics of elite youth soccer players. Two groups (age: 14.4 years) participated in this study: 1) 24 soccer players training 8 to 10 hours per week and 2) 26 non-athletic boys used as controls. Anthropometric measurements, aerobic (Yo-Yo Intermittent Recovery test level 1) and anaerobic (counter-movement-jump (CMJ), squat-jump (SqJ), five-jump-test (5JT), and speed (T5m, 10 m, 30 m)) performances were assessed twice during 8 months (T0: October; T1: May) of the competitive season. Data showed significant differences in height and weight at T0 between the two groups (P < 0.05), while no difference in the percentage of body fat (%BF) was observed. However, the soccer players were significantly taller and had lower %BF than age-matched controls at T1. Compared to the controls, the soccer players attained better results in the physical fitness test (P < 0.05) at T0 and T1 except in (T5m) sprinting speed. Hence, significant improvements (P < 0.05) in physical parameters were observed between T0 and T1 only in soccer players. The results demonstrate that soccer-training season was able to provide maturation free improvement in anthropometric and performance characteristics in young soccer players during the training season.

Static Stretching of the Hamstring Muscle for Injury Prevention in Football Codes: a Systematic Review

To evaluate the relationship between aerobic and intermittent capacities in a team of professional futsal players. FIFTEEN FUTSAL PLAYERS FROM BRAZILIAN FIRST DIVISION (AGE: 25.9±5.1 yrs; height: 1.77±0.04 m, body mass: 74.37±6.02 kg) performed in random order a ramp test and the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) at the start of the season for determination of maximum oxygen consumption (VO2max), peak running speed (Speak), and intermittent running ability. Mean VO2max was of 57.25±6.35 ml·kg(-1)min(-1) with a Speak of 17.69±1.88 km·h(-1). Yo-Yo IR1 performance was of 1,226±282 m. There was no correlation between VO2max and Yo-Yo performance while Speak and Yo-Yo IR1 performance were correlated (r=0.641; P=0.007). From the current results, it may be suggested that both continuous and intermittent physical evaluations are necessary for obtaining a complete fitness profile of futsal players. The low Yo-Yo IR1 performance of Brazilian futsal players when compared to other elite team sport athletes warrants further investigation.

Influence of Neuromuscular Fatigue on Accelerometer Load in Elite Australian Football Players

To determine the impact of neuromuscular fatigue (NMF) assessed from variables obtained during a countermovement jump on exercise intensity measured with triaxial accelerometers (load per minute [LPM]) and the association between LPM and measures of running activity in elite Australian Football. Seventeen elite Australian Football players performed the Yo-Yo Intermittent Recovery Test level 2 (Yo-Yo IR2) and provided a baseline measure of NMF (flight time:contraction time [FT:CT]) from a countermovement jump before the season. Weekly samples of FT:CT, coaches' rating of performance (votes), LPM, and percent contribution of the 3 vectors from the accelerometers in addition to high-speed-running meters per minute at >15 km/h and total distance relative to playing time (m/min) from matches were collected. Samples were divided into fatigued and nonfatigued groups based on reductions in FT:CT. Percent contributions of vectors to LPM were assessed to determine the likelihood of a meaningful difference between fatigued and nonfatigued groups. Pearson correlations were calculated to determine relationships between accelerometer vectors and running variables, votes, and Yo-Yo IR2 score. Fatigue reduced the contribution of the vertical vector by (mean ± 90% CI) -5.8% ± 6.1% (86% likely) and the number of practically important correlations. NMF affects the contribution of individual vectors to total LPM, with a likely tendency toward more running at low speed and less acceleration. Fatigue appears to limit the influence of the aerobic and anaerobic qualities assessed via the Yo-Yo IR2 test on LPM and seems implicated in pacing.

Seasonal Changes in Physical Performance and Heart Rate Variability in High Level Futsal Players

The aim of this study was to determine the changes in physical performance and resting heart rate variability (HRV) in professional futsal players during the pre-season and in-season training periods. 11 athletes took part in the study (age=24.3±2.9 years; height=176.3±5.2 cm; weight=76.1±6.3 kg), and performed a repeated-sprint ability (RSA) test [6×40 m (20+20 m with a 180° change of direction) sprints separated by 20 s of passive recovery] and Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) at 3 different moments (M1=beginning of pre-season; M2=end of pre-season; M3=mid in-season). The HRV indices were assessed at the same moments. After the short pre-season (3-week), mean RSA time (RSAmean) (M1=7.43±0.2 s; M2=7.24±0.2 s; P=0.003), decrement in RSA performance (RSAdecrement) (M1=6.7±0.3%; M2=5.0±0.9%; P=0.001), and Yo-Yo IR1 distance (M1=1.244±298 m; M2=1.491±396 m; P=0.002) were significantly improved (P<0.05). During the in-season (i. e., M3), performance in Yo-Yo IR1 and RSAmean were maintained. In contrast, RSAbest (M2=6.89±0.2 to M3=6.69±0.3; P=0.001) was improved and RSAdecrement (M2=5.0±0.9% to M3=6.6±0.9%; P=0.001) was impaired. At M2, there was an increase in HRV vagal-related indices compared with M1 that was maintained at M3. In conclusion, after a short pre-season, futsal players improved their RSA and Yo-Yo IR1 performance with concomitant improvements in HRV. These indices were maintained during the in-season period while RSAbest was improved and RSAdecrement impaired. Frequent monitoring of these performances and HRV indices may assist with identification of individual training adaptations and/or early signs of maladaption.

The Yo-Yo Intermittent Recovery Test in Junior Basketball Players According to Performance Level and Age Group

The aim of this study was to evaluate the Yo-Yo Intermittent Recovery Test Level 1 (Yo-Yo IR1) ability to discriminate between elite, subelite junior basketball players, and a group of nonathletic healthy male athletes at 3 different age groups (U-14 to U-17). In a cross-sectional design, 119 age-matched participants spread over 3 groups, elite (n = 46), subelite (n = 42) junior basketball players, and nonathletic healthy male athletes (n = 31), were evaluated over a 5-week period. The participants undertook 2 familiarization trials of the Yo-Yo test performance and 3 test sessions on an indoor basketball court. When controlling for the effect of the participants' body mass, the results showed that elite athletes had a significantly higher Yo-Yo performance compared with the subelite athletes (1,271 ± 385 vs. 861 ± 428 m; p < 0.0017; effect size [ES] 1.0 ± 0.35) and the nonathletic group (1,271 ± 385 vs. 738 ± 345 m; p < 0.0017; ES 1.45 ± 0.38). No statistical differences (p > 0.0017; ES from 0.02 to 0.39) were noted between participants' performance levels across age groups. Typical between-performance levels and -age groups differences in the Yo-Yo IR1 were observed. However, when controlling for the effect of the participants' body mass, this study demonstrates that the Yo-Yo test is accurate only to discriminate elite junior basketball players but cannot be used to differentiate the basketball-specific aerobic performance for age.

Effects of an Individualized Soccer Match Simulation on Vertical Stiffness and Impedance

An observed relationship between soccer match duration and injury has led to research examining the changes in lower extremity mechanics and performance with fatiguing exercise. Because many fatigue protocols are designed to result in substantial muscular deficits, they may not reflect the fatigue associated with sport-specific demands that have been associated with the increasing incidence of injury as the match progresses. Thus, the aim of this study was to systematically analyze the progressive changes in lower extremity mechanics and performance during an individualized exercise protocol designed to simulate a 90-minute soccer match. Previous match analysis data were used to systematically develop a simulated soccer match exercise protocol that was individualized to the participant's fitness level. Twenty-four National Collegiate Athletic Association Division I soccer players (12 men, 12 women) participated in 2 testing sessions. In the first session, the participants completed the Yo-Yo Intermittent Recovery Test Level 1 to assess their fitness level and determine the 5 submaximal running intensities for their soccer match simulation. In the second test session, progressive changes in the rating of perceived exertion (RPE), lower extremity performance (vertical jump height, sprint speed, and cutting speed), and movement mechanics (jumping vertical stiffness and terminal landing impedance) were measured during the soccer match simulation. The average match simulation running distance was 10,165 ± 1,001 m, consistent with soccer match analysis research. Time-related increases in RPE, and decrements in sprinting, and cutting speed were observed, suggesting that fatigue increased as the simulation progressed. However, there were no time-related decreases in vertical jump height, changes in lower extremity vertical stiffness in jumping, or vertical impedance during landing. Secondary analyses indicated that the coordinative changes responsible for the maintenance of stiffness and impedance differed between the dominant and nondominant limbs. Despite an increase in RPE to near exhaustive levels, and decrements in sprint and cutting performance, the participants were able to maintain jump performance and movement mechanics. Interestingly, the coordinative changes that allowed for the maintenance of vertical stiffness and impedance varied between limbs. Thus, suggesting that unilateral training for performance and injury prevention in soccer-specific populations should be considered.

Relative Age Effect and Yo-Yo IR1 in Youth Soccer

The aims of the study were to investigate the presence of a relative age effect and the influence of birth quarter on anthropometric characteristics, an estimation of biological maturity and performance in the Yo-Yo Intermittent Recovery Test level 1 in 606 elite, Flemish youth soccer players. The sample was divided into 5 chronological age groups (U10-U19), each subdivided into 4 birth quarters. Players had their APHV estimated and height, weight and Yo-Yo IR1 performance were assessed. Differences between quarters were investigated using uni- and multivariate analyses. Overall, significantly (P<0.001) more players were born in the first quarter (37.6%) compared to the last (13.2%). Further, no significant differences in anthropometric variables and Yo-Yo IR1 performance were found between the 4 birth quarters. However, there was a trend for players born in the first quarter being taller and heavier than players born in the fourth quarter. Players born in the last quarter tended to experience their peak in growth earlier, this may have enabled them to compete physically with their relatively older peers. Our results indicated selection procedures which are focused on the formation of strong physical and physiological homogeneous groups. Relative age and individual biological maturation should be considered when selecting adolescent soccer players.

EVALUATION OF AEROBIC CAPACITY IN SOCCER PLAYERS: COMPARISON OF FIELD AND LABORATORY TESTS

The purpose of this study was to evaluate the maximal oxygen uptake ( · VO2max) values in soccer players as assessed by field and laboratory tests. Fourteen amateur soccer players (mean age: 21.9 ± 2.5) performed 2 maximal field tests: the Yo-Yo intermittent recovery test level 1 (YIRT), and the 20-m multi-stage shuttle run test (MST), as well as 1 maximal test on the treadmill with the Bruce treadmill test (BTRT) protocol. A portable telemetric ergospirometry device was used during all the tests to determine · VO2max. In addition, an estimated · VO2max value was calculated for players after all the tests. At the end of the study, no significant differences were found between field and laboratory tests in terms of measured · VO2max, HRmax and respiratory exchange ratio (RER) (p>0.05), whereas significant differences were found between field and laboratory tests in terms of estimated · VO2max (p<0.05). In addition, there were no significant differences between measured · VO2 and estimated · VO2max in BTRT, whereas significant differences were found between measured · VO2max and estimated · VO2max in both YIRT and MST. Finally, while there was a strong relationship between · VO2max and both MST and BTRT performance (distance covered), there was a moderate correlation between · VO2max and YIRT performance. This study results suggest that it is necessary to use ergospirometry to accurately estimate aerobic capacity in soccer players. In addition, both MST and YIRT could be used to determine HRmax of players, and MST has a strong relationship with · VO2max. Thus MST may also be a more favourable field-based assessment

The effect of Ramadan fasting on the diurnal variations in aerobic and anaerobic performances in Tunisian youth soccer players

The purpose of this investigation was to assess the effects of Ramadan fasting on physical performance in youth Muslim athletes their diurnal fluctuations. In a balanced and randomized study design, 10 Tunisian junior male soccer players completed the Yo-Yo intermittent recovery test level 1 (YYIRT) and the repeated sprint ability (RSA) at 07:00 and 17:00 h on three different occasions: 1 week before Ramadan (BR), the second week of Ramadan (SWR) and the fourth week of Ramadan (ER). There was an interval of 36 h between any two successive tests. Oral temperature was measured before each test. Under each condition, the results showed a time-of-day effect on oral temperature. However, no significant diurnal variations in rate of perceived exertion (RPE) scores were observed during the three periods (BR, SWR and ER). Performances during the YYIRT and the first two sprints of the RSA improved significantly from morning to evening during BR. However, daily fluctuations disappeared during the SWR and ER. Considering the effect of Ramadan on physical performances, in comparison with BR, no significant difference was observed during Ramadan at 07:00 h. However, the variables were significantly lower in SWR and ER at 17:00 h. The RPE scores were higher during SWR and ER in the evening after the YYIRT and RSA tests. In conclusion, the time-of-day effects on physical performances variables tend to disappear during Ramadan. In comparison with the period BR, physical performances were unaffected at 07:00 h but impaired at 17:00 h during Ramadan.

β-alanine supplementation improves YoYo intermittent recovery test performance

Backgroundβ-alanine supplementation has been shown to improve high-intensity exercise performance and capacity. However, the effects on intermittent exercise are less clear, with no effect shown on repeated sprint activity. The aim of this study was to investigate the effects of β-alanine supplementation on YoYo Intermittent Recovery Test Level 2 (YoYo IR2) performance.MethodsSeventeen amateur footballers were allocated to either a placebo (PLA; N = 8) or β-alanine (BA; N = 9) supplementation group, and performed the YoYo IR2 on two separate occasions, pre and post 12 weeks of supplementation during a competitive season. Specifically, players were supplemented from early to mid-season (PLA: N = 5; BA: N = 6) or mid- to the end of the season (PLA: N = 3; BA: N = 3). Data were analysed using a two factor ANOVA with Tukey post-hoc analyses.ResultsPre supplementation scores were 1185 ± 216 and 1093 ± 148 m for PLA and BA, with no differences between groups (P = 0.41). YoYo performance was significantly improved for BA (+34.3%, P ≤ 0.001) but not PLA (−7.3%, P = 0.24) following supplementation. 2 of 8 (Early – Mid: 2 of 5; Mid – End: 0 of 3) players improved their YoYo scores in PLA (Range: -37.5 to + 14.7%) and 8 of 9 (Early – Mid: 6 of 6; Mid – End: 2 of 3) improved for BA (Range: +0.0 to +72.7%).Conclusions12 weeks of β-alanine supplementation improved YoYo IR2 performance, likely due to an increased muscle buffering capacity resulting in an attenuation of the reduction in intracellular pH during high-intensity intermittent exercise.

Differences in Body Composite and Physical Match Performance in Female Soccer Players According to Team Position

Milanovic Z, Sporis G, Trajkovic N. Differences in Body Composite and Physical Match Performance in Female Soccer Players According to Team Position. J. Hum. Sport Exerc. Vol. 7, No. Proc1, pp. S67-S72, 2012. The aim of this research was to determine the differences between body composition and physical match performance among female soccer players according to the team’s position. Twenty two elite female soccer players (aged 23.95 ± 4.52, height 168.82 ± 7.19 cm, body mass index 21.5 ± 1.3kg) from Serbian A-national team participated in this study. Players were tested for aerobic endurance, Yo-Yo intermittent recovery test level 1 (YYIRL1), body mass and body height. The percentage of body fat and body mass index (BMI) was determinate according to body height and body weight parameters. The average value of body weight among female soccer players has been 61.4±6.0kg. The biggest average value for body weight has been found among midfielders 62.7±7.7kg, while the smallest values have been found among goalkeepers 59.5±10.6kg. Opposite to the body weight, goalkeepers have been the tallest players with average body high of 172.5±3.5cm, than the defenders with 170.0±7.2cm, while the midfielders (168.7±8.7cm) and the attackers (164.7±5.0cm) have shown the smallest average values. The YYIRL1 test’s results have shown that all positions have similar value within range of 880-930m, which indicates group homogeneity. The average values of the body fat was 25.9±2.0%. Significant difference between the tested variables according to the player’s position in the team could not be established (p<0.05). The selection process and the orientation towards specific team position represent an important aspect of the realization of the top athletic results, but it cannot be based merely on morphological and functional results. According to this research, differences cannot be precisely defined in both morphological and functional abilities of the women soccer players based on their position in the team. Key words: YO-YO TEST, BODY MASS, FEMALE, SOCCER.

N-Acetylcysteine’s Attenuation of Fatigue After Repeated Bouts of Intermittent Exercise: Practical Implications for Tournament Situations

Production of reactive oxygen species (ROS) during muscle contractions is associated with muscle fatigue and damage in the short term and adaptive responses in the long term. When adaptation is inconsequential acute antioxidant supplementation may be able to attenuate muscle fatigue and damage to enhance performance. This study aimed to determine the effects of acute oral N-acetylcysteine (NAC) supplementation on Yo-Yo Intermittent Recovery Test Level 1 (YIRT-L1) performance after repeated bouts of damaging intermittent exercise. In a pair-matched design, 12 recreationally trained men engaged in 6 d of either NAC (n = 6) or placebo (n = 6) supplementation. After a treatment-loading day, participants completed 3 testing sessions, on alternating days, consisting of a preexercise isokinetic dynamometry (IKD) test, a damaging intermittent-exercise protocol, YIRT-L1, and a postexercise IKD test. Another IKD test was completed on the 2 intervening d. NAC treatment resulted in a significant preservation of YIRT-L1 performance (p ≤ .0005). IKD performance significantly deteriorated over time at all contraction speeds, and this deterioration was not influenced by treatment group. Plasma creatine kinase values increased significantly over time (p = .002) and were significantly greater in the NAC group than in the placebo group (p = .029). NAC induced mild gastrointestinal side effects. NAC supplementation may be a useful strategy to enhance performance during short-term competitive situations when adaption is inconsequential. Titration studies to elucidate a treatment dose that enhances performance without inducing side effects are now required.

Discriminative Ability of The Yo-Yo Intermittent Recovery Test (Level 1) in Prospective Young Soccer Players

We evaluated the sensitivity of the Yo-Yo intermittent recovery test-level 1 (Yo-Yo IR1) when discriminating among players in varying playing positions and different age categories in youth soccer. One-hundred and six prospective young soccer players, grouped on the basis of chronological age (under-13, under-14, under-15, under-16, under-17, under-18, and under-19) and playing position (center-backs, fullbacks, center midfielders, wide midfielders, and forwards), participated in the study. The players were administered a single Yo-Yo IR1 test at the beginning of the spring season. Analysis of variance revealed significant (F = 25.3; p < 0.001) group differences in Yo-Yo IR1 test performance scores among the observed age categories, and a systematic age-related increase in the Yo-Yo IR1 test performance was evident. Subsequent post hoc comparisons identified a number of significant differences among the selected age categories in Yo-Yo IR1 test performance. Analysis of covariance identified significant differences among playing positions (F = 3.1; p < 0.019) in the Yo-Yo IR1 test performance after controlling for age (F = 135.1; p < 0.001). Subsequent pairwise comparisons of the adjusted Yo-Yo IR1 test performance identified that center-backs had achieved significantly lower (all p < 0.01) performance scores than center midfielders, wide midfielders, and forwards, but not fullbacks. These results could be of practical value to coaches and scientists for further development of talent selection and profiling procedures in soccer, particularly because (a) the endurance performance represents a very important fitness component in selection and profiling of young soccer players and (b) the Yo-Yo IR1 test proved to be valid, reliable, and easily available measurement tool of a player's soccer-specific endurance capacity.

Yo-Yo IR2 test e teste de margaria: validade, confiabilidade e obtenção da frequência cardíaca máxima em jogadores jovens de futebol

Os objetivos do presente estudo foram: i) avaliar a validade de constructo do Yo-Yo Intermittente Recovery Test Level 2 (Yo-Yo IR2) e do teste de Margaria (TM) com o desempenho em alta intensidade de exercício durante jogos oficiais em jogadores de futebol; ii) verificar a confiabilidade (teste-reteste) dos dois testes; iii) comparar os valores da frequência cardíaca máxima (FCM) obtida nesses protocolos e em jogo. Dezoito jogadores (média ± DP; idade 14 ± 0,8 anos, estatura 172 ± 9cm, peso 64,3 ± 8,5kg) pertencentes à mesma equipe foram avaliados em teste-reteste nos referidos protocolos e no percentual de tempo de permanência acima de 85% da FCM individual (PTP&gt;85%FCM) em dois jogos oficiais do Campeonato Mineiro Infantil. Uma alta correlação foi encontrada entre o desempenho no Yo-Yo IR2 e PTP&gt;85%FCM (rs = 0,71; p &lt; 0,05). Não houve correlação estatisticamente significante entre o desempenho no TM e PTP&gt;85%FCM (rs = 0,44; p = 0,06). O Yo-Yo IR2 se mostrou mais variável e menos reprodutível (CV = 11%; CCI [95% IC] = 0,38) do que TM (CV = 1%; CCI [95% IC] = 0,93). O maior valor de FCM (p &lt; 0,001) ocorreu no jogo (202 ± 8bpm). A FCM no Yo-Yo IR2 (194 ± 4bpm) foi menor (p &lt; 0,006) do que TM (197 ± 6bpm). Conclui-se que o Yo-Yo IR2 pode ser considerado mais válido para predizer a manutenção de alta intensidade de exercício em jogo que é uma importante medida de desempenho no futebol. Porém, há necessidade de padronização rigorosa entre os procedimentos de avaliação para estabilidade da medida. A FCM deve ser observada em diversas situações, principalmente competitiva, para possibilitar que ocorra o maior valor individual.

Physiological and performance adaptations to an in‐season soccer camp in the heat: Associations with heart rate and heart rate variability

The aim of the present study was to examine the associations between adaptive responses to an in-season soccer training camp in the heat and changes in submaximal exercising heart rate (HRex, 5-min run at 9 km/h), postexercise HR recovery (HRR) and HR variability (HRV). Fifteen well-trained but non-heat-acclimatized male adult players performed a training week in Qatar (34.6 ± 1.9°C wet bulb globe temperature). HRex, HRR, HRV (i.e. the standard deviation of instantaneous beat-to-beat R-R interval variability measured from Poincaré plots SD1, a vagal-related index), creatine kinase (CK) activity, plasma volume (PV) changes, and post-5-min run rate of perceived exertion (RPE) were collected at six occasions in temperate environmental conditions (22°C). Players also performed the yo-yo intermittent recovery test level 1 (Yo-Yo IR1) in the same environmental conditions (22°C), both at the beginning and at the end of the training week. Throughout the intervention, HRex and HRV showed decreasing (P < 0.001) and increasing (P < 0.001) trends, respectively, while HRR remained unaffected (P = 0.84). Changes in HRex [-0.52, 90% confidence limits (-0.64; -0.38), P < 0.001] and SD1 [0.35 (0.19; 0.49), P < 0.001] were correlated with those in PV. There was no change in RPE (P = 0.92), while CK varied according to training contents (P < 0.001), without association with HR-derived measures. Yo-Yo IR1 performance increased by 7 ± 9% (P = 0.009), which was correlated with changes in HRex [-0.64 (-0.84; -0.28), P = 0.01]. In conclusion, we found that an in-season soccer training camp in the heat can significantly improve PV and soccer-specific physical performance; both of which are associated with changes in HRex during a 5-min submaximal run.

The relationship between physical capacity and match performance in elite Australian football: A mediation approach

The aim of this study was to verify if yo-yo intermittent recovery test (level 2) (yo-yo IR2) score is linked to Australian football (AF) performance through match exercise intensity. Six week prospective study design. Twenty-one data sets were recorded from nine individual players that completed the yo-yo IR2, and played an Australian Football League match in the first five rounds of the 2010 season wearing a global positioning system (GPS) unit. Simple mediation modelling was used to analyse the inter-relationship between yo-yo IR2 score, match exercise intensity and AF performance. Playing position and experience were also incorporated into the model to identify conditional affects. A significant direct relationship was observed between yo-yo IR2 and number of ball disposals ( p < 0.1) and a significant indirect relationship was observed between yo-yo IR2 and number of ball disposals through distance travelled at high intensity (HIR m min −1) ( p < 0.1). Moderation analysis showed that playing position affected the relationship between of yo-yo IR2 and HIR m min −1 ( p < 0.1) and HIR m min −1 and total ball disposals ( p < 0.1). Playing experience also significantly affected the relationship between HIR m min −1 and total ball disposals. This study is the first to identify the effects of yo-yo IR2 on total ball disposals through HIR m min −1 performed during AF matches, and that playing position and playing experience affect these interactions.