Caffeine supplementation does not affect match activities and fatigue resistance during match play in young football players.

Abstract The study examined the effect of caffeine supplementation on match activities and development of fatigue during a football match. In a randomised, double-blind cross-over design, two experimental football games separated by 7 days were organised between the junior teams of two professional football clubs (17.6 ± 1.1 years (±s), 71.7 ± 6.9 kg, 13.9% ± 5.0% body fat). The players ingested either a capsule of 6 mg · kg-1 b.w. caffeine or placebo (dextrose) 65 min prior to the matches. Match activities were assessed using the ZXY match analysis system, and a Yo-Yo intermittent recovery test-level 2 (Yo-Yo IR2) was conducted immediately post-game. Heart rate was monitored throughout the game, and blood samples were obtained at baseline, half-time and after the game. There were no differences between caffeine and placebo regarding total distance covered (10,062 ± 916 vs 9854 ± 901 m), high-intensity running (557 ± 178 vs 642 ± 240 m), sprinting distance (109 ± 58 vs 112 ± 69 m) or acceleration counts (123 ± 31 vs 126 ± 24). In both trials, players displayed lower (P < 0.05) values in total distance and acceleration counts in the last 15 min compared to all other 15-min periods of the matches. Post-game Yo-Yo IR2 performance was not different between game trials (caffeine: 829 ± 322 m; placebo 819 ± 289 m). In conclusion, oral caffeine administration does not appear to have an ergogenic effect in young football players during match play.

Heart rate response and fitness effects of various types of physical education for 8- to 9-year-old schoolchildren.

The present study investigated the heart rate (HR) response to various types of physical education (PE) activities for 8- to 9-year-olds (five school classes, n = 93) and the fitness effects of a short-term PE training programme (three of the five classes, n = 59) with high compared to low-to-moderate aerobic intensity. HR was recorded during small-sided indoor soccer (SO), basketball (BB), unihockey (UH), circuit training (CT), walking (W) and Nintendo Wii Boxing (NWB) and Nintendo Wii Tennis (NWT). Maximal HR (HRmax) and physical fitness was determined by the Yo-Yo Intermittent Recovery Level 1 Children's test (YYIR1C) test. Following cluster randomisation, three classes were tested before and after 6 wks with 2 × 30 min/wk SO and UH lessons [high-intensity (HI), 2 classes, n = 39] or low-to-moderate intensity PE lessons (CON, 1 class, n = 20). Average HR in SO (76 ± 1% HRmax), BA (77 ± 1% HRmax) and UH (74 ± 1% HRmax) was higher (P < 0.05) than in CT (62 ± 1% HRmax), W (57 ± 1% HRmax), NWB (65 ± 2% HRmax) and NWT (57 ± 1% HRmax). Time with HR > 80% and 90% HRmax, respectively, was higher (P < 0.05) in SO (42 ± 4 and 12 ± 2%), BB (41 ± 5 and 13 ± 3%) and UH (34 ± 3 and 9 ± 2%) than in CT, W and NW (0-5%), with time >80% HRmax being higher (P < 0.05) in SO than UH. After 6 wk, YYIR1C performance was increased (P < 0.05) by 22% in HI (673 ± 57 to 821 ± 71 m), but unaltered in CON (674 ± 88 to 568 ± 81 m). HR 2 min into YYIR1C was lowered (P < 0.05) in HI after 6 wks (92.4 ± 0.8 to 89.1 ± 0.9% HRmax), but not in CON. In conclusion, ball games elicited high aerobic loading for young schoolchildren and a short-term, low-volume ball game PE-intervention improved physical fitness. Traditional PE sessions had no effects on intermittent exercise performance.

Application of the Copenhagen Soccer Test in high-level women players - locomotor activities, physiological response and sprint performance.

We evaluated the physiological response, sprint performance and technical ability in various phases of the Copenhagen Soccer Test for Women (CSTw) and investigated whether the locomotor activities of the CSTw were comparable to competitive match-play (CM). Physiological measurements and physical/technical assessments were performed during CSTw for eleven Norwegian high-level women soccer players. The activity pattern during CSTw and CM was monitored using the ZXY tracking system. No differences were observed between CSTw and CM with regards to total distance covered (10093±94 and 9674±191m), high intensity running (1278±67 and 1193±115m) or sprinting (422±55 and 372±46m) (p>.05). During CSTw, average HR was 85±2%HRmax with 35±2% playing time >90%HRmax. Blood lactate increased (p<.05) from 1.4±0.3mM at rest to an average of 4.7±0.5mM during CSTw, with no changes during the test. Blood glucose was 5.4±0.3mM at rest and remained unaltered during CSTw. Sprint performance (2×20m) decreased (p<.05) by 3% during CSTw (8.19±0.06-8.47±0.10s). In conclusion, the locomotor activities during CSTw were comparable to that of high-level competitive match-play. The physiological demands of the CSTw were high, with no changes in heart rate, blood lactate or technical performance during the test, but a lowered sprint performance towards the end of the test.

Cardiovascular health profile of elite female football players compared to untrained controls before and after short-term football training.

This study examined the intermittent exercise performance and cardiovascular health profile in elite female football players in comparison to untrained young women, as well as a subgroup subjected to football training 2x1 h · week(-1) for 16 weeks. Twenty-seven Danish national team players (elite trained, ET) and 28 untrained women (UT) underwent dual-energy X-ray absorptiometry-scanning (DXA), comprehensive transthoracic echocardiography, treadmill and Yo-Yo Intermittent Endurance level 2 (IE2) testing. Eight women in UT were also tested after the football training period. Maximal oxygen uptake rate (VO2max), peak ventilation and peak lactate were 40, 18 and 51% higher (P< 0.01) in ET than UT, respectively. Cardiac dimensions and function were greater in ET than UT, with left ventricular diastolic diameter, right ventricular diastolic diameter, tricuspid annular plane systolic excursion (TAPSE) and peak transmitral flow in early diastole divided by peak transmitral flow velocity in late diastole during atrial contraction (E/A-ratio) being 13, 19, 27 and 41%, respectively, greater in ET than UT (P< 0.001 to< 0.05). Yo-Yo IE2 performance was 7-fold higher in ET than UT (1772 ± 508 vs. 234 ± 66 m, P< 0.001), fat mass was 51% lower (P< 0.001) and high density lipoprotein (HDL) cholesterol levels were 20% higher (P< 0.01). Sixteen weeks of football elevated VO2max and Yo-Yo IE2 performance by 16 and 40%, respectively, and lowered fat mass by 6%. Cardiac function was markedly improved by 16 weeks of football training with 26 and 46% increases in TAPSE and E/A ratio, respectively, reaching levels comparable to ET. In summary, elite female football players have a superior cardiovascular health profile and intermittent exercise performance compared to untrained controls, but short-term football training can markedly improve the cardiovascular health status.

The use of Yo-Yo intermittent recovery level 1 and Andersen testing for fitness and maximal heart rate assessments of 6- to 10-year-old school children.

We evaluated a submaximal and maximal version of the Yo-Yo intermittent recovery level 1 children's (YYIR1C) test and the Andersen test for fitness and maximal heart rate assessments of children aged 6-10 years. Two repetitions of the YYIR1C and Andersen tests were carried out within 1 week by 6- to 7-year-olds and 8- to 9-year-olds (grade 0, n = 17; grade 2, n = 16) and 6 weeks apart by 9- to 10-year-olds (grade 3, n = 49). Grade 0-2 pupils also performed an incremental treadmill test (ITT). Grade 2 pupils had a better (p < 0.05) YYIR1C (84%; 994 ± 399 m (±SD) vs. 536 ± 218 m) and Andersen test performance (10%; 1,050 ± 71 m vs. 955 ± 56 m) than grade 0 pupils. For grade 0-2 pupils, YYIR1C, Andersen, and ITT peak heart rates were 205 ± 11, 207 ± 9, and 203 ± 7 b·min(-1), respectively (Andersen > ITT, p < 0.05), and for grade 3 pupils, YYIR1C and Andersen peak heart rates were 208 ± 9 and 204 ± 9 b·min(-1), respectively (YYIR1C > Andersen, p < 0.05). Submaximal YYIR1C heart rate (HR) was inversely correlated (p < 0.05) with YYIR1C test performance (r = -0.54 to -0.67) and VO2peak (r = -0.42). The 6-week change in submaximal HR correlated with the change in YYIR1C test performance (r = -0.42 to -0.53, p < 0.05). In conclusion, YYIR1C and Andersen tests are simple and inexpensive intermittent field tests that can detect differences in fitness levels and determine maximal HR of 6- to 10-year-old children. Additionally, submaximal YYIR1C testing can be used for frequent nonexhaustive fitness assessments.

Kicking velocity and physical, technical, tactical match performance for U18 female football players--effect of a new ball.

We investigated kicking velocity and physical, technical, and tactical match performance for under-18 (U18) female football players and evaluated the effect of using a newly developed lighter smaller ball. Ten regional league teams participated. Maximal ball velocity was 4±1% higher when kicking the new ball (NB) compared with the standard ball (SB) in a laboratory testing situation (23.2±0.4 vs. 22.4±0.3 ms(-1); p<.05). Mean HR was similar during games with NB and SB (169±2 vs. 170±2 bmin(-1); p>.05), but lower-limb muscular RPE was lower with NB (4.2±0.4 vs. 5.2±0.3; p<.05). The number of activity changes (1387±76 vs. 1401±55), total distance covered (9.09±0.25 vs. 9.11±0.25 km) and high-intensity running (1.04±0.08 vs. 1.11±0.07 km) were not different between NB and SB (p>.05). High-intensity running decreased (p<.05) from 0-20 to 60-80 min with NB (34%) and SB (37%). The number and success rate of long and short passes did not differ between NB and SB (p>.05). In conclusion, physiological demands were high in youth female football games, and decrements in running performance occurred towards the end of games. The players kicked faster and reported lower muscular exertion during games played with a lighter smaller ball, but locomotor activities, heart rate and overall technical-tactical game performance remained unaffected.

Yo-Yo IR2 testing of elite and sub-elite soccer players: performance, heart rate response and correlations to other interval tests.

We examined performance, heart rate response and construct validity of the Yo-Yo IR2 test by testing 111 elite and 92 sub-elite soccer players from Norway and Denmark. VO2max, Yo-Yo IR1 and repeated sprint tests (RSA) (n = 51) and match-analyses (n = 39) were also performed. Yo-Yo IR2 and Yo-Yo IR1 performance was 41 and 25% better (P < 0.01) for elite than sub-elite players, respectively, and heart rate after 2 and 4 min of the Yo-Yo IR2 test was 20 and 15 bpm (9 and 6% HRmax), respectively, lower (P < 0.01) for elite players. RSA performance and VO2max was not different between competitive levels (P > 0.05). For top-teams, Yo-Yo IR2 performance (28%) and sprinting distance (25%) during match were greater (P < 0.05) than for bottom-teams. For elite and sub-elite players, Yo-Yo IR2 performance was correlated (P < 0.05) with Yo-Yo IR1 performance (r = 0.74 and 0.76) and mean RSA time (r = -0.74 and -0.34). We conclude that the Yo-Yo IR2 test has a high discriminant and concurrent validity, as it discriminates between players of different within- and between-league competitive levels and is correlated to other frequently used intermittent elite soccer tests.

Reliability, sensitivity and validity of the assistant referee intermittent endurance test (ARIET) - a modified Yo-Yo IE2 test for elite soccer assistant referees.

We examined the reliability and validity of the assistant referee intermittent endurance test (ARIET), a modified Yo-Yo IE2 test including shuttles of sideways running. The ARIET was carried out on 198 Italian (Serie A-B, Lega-Pro and National Level) and 47 Danish elite soccer assistant referees. Reproducibility was tested for 41 assistant referees on four occasions each separated by one week. The ARIET intraclass correlation coefficients and typical error of measurement ranged from 0.96 to 0.99 and 3.1 to 5.7%, respectively. ARIET performance for Serie A and B was 23 and 25% greater than in Lega-Pro (P < 0.001). The lowest cut-off value derived from receiving operator characteristic discriminating Serie A-B from Lega-Pro was 1300 m. The ARIET performance was significantly correlated with VO(2max) (r = 0.78, P < 0.001), %HR(max) after 4 min of ARIET (r = - 0.81, P < 0.001) and Yo-Yo IR1 performance (r = 0.95, P < 0.001), but not sprint performance (r = -0.15; P = 0.58). The results showed that ARIET is a reproducible and valid test that is able to discriminate between assistant referees of different competitive levels. The lack of correlation with sprinting ability and close correlations with aerobic power, intermittent shuttle running and sub-maximal ARIET heart rate loading provide evidence that ARIET is a relevant test for assessment of intermittent endurance capacity of soccer assistant referees.

The Copenhagen Soccer Test: physiological response and fatigue development.

INTRODUCTION: The aims of the study were 1) to evaluate whether a multifaceted simulated soccer game protocol, entitled the Copenhagen Soccer Test (CST), elicited a similar physiological loading as a competitive game (CG) and 2) to determine muscle metabolites, blood variables, and sprint performance in various phases of CST. METHODS: Twelve Danish Second- and Third-Division soccer players participated in the study. On separate days, HR measurements, frequent blood sampling, and physical/technical tests were performed during 60- and 90-min versions of the CST during which repeated musculus vastus lateralis biopsies were collected. A CG was also played, where HR was recorded and pre- and post-game muscle biopsies and blood samples were collected. RESULTS: No differences were observed between CST and CG in average HR (85% ± 1% and 86% ± 1% HRmax, P > 0.05) or recovery plasma creatine kinase (24 h: 312 ± 57 and 324 ± 76 U·L, P > 0.05). Muscle glycogen decreased (P < 0.05) from 459 ± 15 to 232 ± 30 mmol·kg dry weight (d.w.) during CST, which was not different from CG (P > 0.05). The rate of glycogen utilization was 4 ± 1 mmol·kg d.w.·min during the warm-up and the first 15 min of CST and 1 ± 1 mmol·kg d.w.·min (P < 0.05) from 60 to 90 min of CST. After 15 min of CST, muscle lactate was elevated (P < 0.05) approximately fivefold (24 ± 3 mmol·kg d.w.), and creatine phosphate was lowered (P < 0.05) by ∼60% (28 ± 4 mmol·kg d.w.). Sprint velocity (2 × 20 m) decreased (P < 0.05) by 7% during CST (5.2 ± 0.6 to 4.9 ± 0.7 m·s). CONCLUSIONS: The physiological response to the CST was reproducible and comparable to that of high-level CG. The CST allowed for rapid muscle sampling and revealed high creatine phosphate degradation throughout the test and a lowered glycogen utilization toward the end of the simulated game.

Elite futsal refereeing: activity profile and physiological demands.

The purpose of this study was to determine the physiological demands and to establish the relationship between activity profile and endurance capacity of futsal referees. Eighteen elite futsal referees (33.0 ± 5.1 years, 173 ± 5 cm, and 73.2 ± 8.4 kg) were studied. Video filming (n = 18) and heart rate (HR) recordings were performed throughout games. Blood lactate (n = 14) was determined at rest and after the game. Endurance capacity was determined with the Yo-Yo IE2. The number of activity changes was as high as 1,395 ± 218 (± SD). Total distance covered, high-intensity running (HIR), sprinting (SPR), and sideways running were 5.89 ± 0.56, 0.96 ± 0.29, 0.09 ± 0.07, and 0.91 ± 0.46 km, respectively. The number of HIR and SPR bouts was 129 ± 41 and 9 ± 8, respectively, with a mean duration of ∼1.4 seconds. Blood lactate content was 1.0 ± 0.3 and 1.5 ± 0.5 mM before and after the game. The amount of HIR performed during the match correlated significantly (r = 0.77; p < 0.05) with the Yo-Yo IE2 performance. Considering the data obtained in the present study, the use of match-specific intermittent fitness tests to evaluate futsal referees seems to be required.