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Jens Bangsbo, Fedon Marcello Iaia and Peter Krustrup

The physical demands in soccer have been studied intensively, and the aim of the present review is to provide an overview of metabolic changes during a game and their relation to the development of fatigue. Heart-rate and body-temperature measurements suggest that for elite soccer players the average oxygen uptake during a match is around 70% of maximum oxygen uptake (VO2 max). A top-class player has 150 to 250 brief intense actions during a game, indicating that the rates of creatine-phosphate (CP) utilization and glycolysis are frequently high during a game, which is supported by findings of reduced muscle CP levels and several-fold increases in blood and muscle lactate concentrations. Likewise, muscle pH is lowered and muscle inosine monophosphate (IMP) elevated during a soccer game. Fatigue appears to occur temporarily during a game, but it is not likely to be caused by elevated muscle lactate, lowered muscle pH, or change in muscle-energy status. It is unclear what causes the transient reduced ability of players to perform maximally. Muscle glycogen is reduced by 40% to 90% during a game and is probably the most important substrate for energy production, and fatigue toward the end of a game might be related to depletion of glycogen in some muscle fibers. Blood glucose and catecholamines are elevated and insulin lowered during a game. The blood free-fatty-acid levels increase progressively during a game, probably reflecting an increasing fat oxidation compensating for the lowering of muscle glycogen. Thus, elite soccer players have high aerobic requirements throughout a game and extensive anaerobic demands during periods of a match leading to major metabolic changes, which might contribute to the observed development of fatigue during and toward the end of a game.

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Anne-Marie Elbe, Svein Barene, Katharina Strahler, Peter Krustrup and Andreas Holtermann

Flow is a rewarding psychological state that motivates individuals to repeat activities. This study explored healthcare workers’ flow experiences during a workplace exercise intervention. Seventy-nine females were assigned to either a 12-week football or Zumba exercise intervention and their flow experiences were assessed at the beginning, midway and at the end of the intervention. The results showed that both intervention groups experienced medium levels of flow and an increase in flow values over time. A significant positive correlation between experiencing flow midway through the intervention and adherence to regular physical activity 18 weeks after the end of the intervention was found. Furthermore, repeated measures throughout the intervention period showed a significantly different development of flow values over time for the adherers and nonadherers. Flow therefore may be of importance for adherence to regular workplace physical activity. Future research needs to investigate the importance of flow in other physical activity settings, especially also for male participants.

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Susana C. A. Póvoas, Carlo Castagna, José Manuel da Costa Soares, Pedro Silva, Manuel Coelho-e-Silva, Fernando Matos and Peter Krustrup

Purpose:

The reliability and construct validity of three age-adapted-intensity Yo-Yo tests were evaluated in untrained (n = 67) vs. soccer-trained (n = 65) 9- to 16-year-old schoolgirls.

Methods:

Tests were performed 7 days apart for reliability (9- to 11-year-old: Yo-Yo intermittent recovery level 1 children’s test; 12- to 13-yearold: Yo-Yo intermittent endurance level 1; and 14- to 16-year-old: Yo-Yo intermittent endurance level 2).

Results:

Yo-Yo distance covered was 40% (776 ± 324 vs. 556 ± 156 m), 85% (1252 ± 484 vs. 675 ± 252 m) and 138% (674 ± 336 vs. 283 ± 66 m) greater (p ≤ .010) for the soccer-trained than for the untrained girls aged 9–11, 12–13 and 14–16 years, respectively. Typical errors of measurement for Yo-Yo distance covered, expressed as a percentage of the coefficient of variation (confidence limits), were 10.1% (8.1–13.7%), 11.0% (8.6–15.4%) and 11.6% (9.2–16.1%) for soccer players, and 11.5% (9.1–15.8%), 14.1% (11.0–19.8%) and 10.6% (8.5–14.2%) for untrained girls, aged 9–11, 12–13 and 14–16, respectively. Intraclass correlation coefficient values for test-retest were excellent (0.795–0.973) in both groups. No significant differences were observed in relative exercise peak heart rate (%HRpeak) between groups during test and retest.

Conclusion:

The Yo-Yo tests are reliable for determining intermittent-exercise capacity and %HRpeak for soccer players and untrained 9- to 16-year-old girls. They also possess construct validity with better performances for soccer players compared with untrained age-matched girls, despite similar %HRpeak.

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Susana Cristina Araújo Póvoas, Peter Krustrup, Carlo Castagna, Pedro Miguel Ribeiro da Silva, Manuel J. Coelho-e-Silva, Rita Liliana Mendes Pereira and Malte Nejst Larsen

Purpose: To examine the reliability of age-adapted submaximal Yo-Yo (Yo-Yosubmax) intermittent tests in untrained schoolchildren aged 9–16 years (n = 139; 72 boys and 67 girls) and within children with high and low percentage of body fat (%BF). Methods: Yo-Yo intermittent recovery level 1 children’s (YYIR1C), Yo-Yo intermittent endurance level 1 (YYIE1), and Yo-Yo intermittent endurance level 2 (YYIE2) tests were performed 7 days apart by 9- to 11-, 12- to 13-, and 14- to 16-year-old children, respectively. Reliability was tested for Yo-Yosubmax heart rate (HRsubmax), peak HR, and maximal distance. Results: HRsubmax typical errors of measurement (TEM) in YYIR1C, YYIE1, and YYIE2 were 2.2% (1.7%–2.9%), 2.4% (1.9%–3.3%), 1.9% (1.6%–2.5%) and 2.4% (1.9%–3.3%), 2.4% (1.9%–3.2%), 1.9% (1.5%–2.4%) for girls and boys, respectively. HRsubmax intraclass correlation coefficient values were good to excellent (.62–.87) in all age groups and in schoolchildren of different %BF. TEM for HRsubmax ranged from 2.1% to 2.3% in high and low %BF groups. Maximal distance intraclass correlation coefficients were excellent and TEM values ranged from 11% to 12% in both %BF groups. HRsubmax was moderately to largely associated (r = −.46 to −.64; P < .002) with Yo-Yo maximal distance across the age groups. Conclusion: Yo-Yosubmax tests are a reliable tool providing useful and sustainable aerobic performance testing in physical education, irrespective of individual %BF.