Peter Krustrup

Match performance of high-standard soccer players with special reference to development of fatigue

The aim of this study was to assess physical fitness, match performance and development of fatigue during competitive matches at two high standards of professional soccer. Computerized time-motion analyses were performed 2-7 times during the competitive season on 18 top-class and 24 moderate professional soccer players. In addition, the players performed the Yo-Yo intermittent recovery test. The top-class players performed 28 and 58% more (P < 0.05) high-intensity running and sprinting, respectively, than the moderate players (2.43 ± 0.14 vs 1.90 ± 0.12 km and 0.65 ± 0.06 vs 0.41 ± 0.03 km, respectively). The top-class players were better (11%; P < 0.05) on the Yo-Yo intermittent recovery test than the moderate players (2.26 ± 0.08 vs 2.04 ± 0.06 km, respectively). The amount of high-intensity running, independent of competitive standard and playing position, was lower (35-45%; P < 0.05) in the last than in the first 15 min of the game. After the 5-min period during which the amount of high-intensity running peaked, performance was reduced (P < 0.05) by 12% in the following 5 min compared with the game average. Substitute players (n = 13) covered 25% more (P < 0.05) ground during the final 15 min of high-intensity running than the other players. The coefficient of variation in high-intensity running was 9.2% between successive matches, whereas it was 24.8% between different stages of the season. Total distance covered and the distance covered in high-intensity running were higher (P < 0.05) for midfield players, full-backs and attackers than for defenders. Attackers and full-backs covered a greater (P < 0.05) distance in sprinting than midfield players and defenders. The midfield players and full-backs covered a greater (P < 0.05) distance than attackers and defenders in the Yo-Yo intermittent recovery test (2.23 ± 0.10 and 2.21 ± 0.04 vs 1.99 ± 0.11 and 1.91 ± 0.12 km, respectively). The results show that: (1) top-class soccer players performed more high-intensity running during a game and were better at the Yo-Yo test than moderate professional players; (2) fatigue occurred towards the end of matches as well as temporarily during the game, independently of competitive standard and of team position; (3) defenders covered a shorter distance in high-intensity running than players in other playing positions; (4) defenders and attackers had a poorer Yo-Yo intermittent recovery test performance than midfielders and full-backs; and (5) large seasonal changes were observed in physical performance during matches.

The Yo-yo Intermittent Recovery Test: Physiological Response, Reliability, and Validity

PURPOSE To examine the physiological response and reproducibility of the Yo-Yo intermittent recovery test and its application to elite soccer. METHODS Heart rate was measured, and metabolites were determined in blood and muscle biopsies obtained before, during, and after the Yo-Yo test in 17 males. Physiological measurements were also performed during a Yo-Yo retest and an exhaustive incremental treadmill test (ITT). Additionally, 37 male elite soccer players performed two to four seasonal tests, and the results were related to physical performance in matches. RESULTS The test-retest CV for the Yo-Yo test was 4.9%. Peak heart rate was similar in ITT and Yo-Yo test (189 +/- 2 vs 187 +/- 2 bpm), whereas peak blood lactate was higher (P < 0.05) in the Yo-Yo test. During the Yo-Yo test, muscle lactate increased eightfold (P < 0.05) and muscle creatine phosphate (CP) and glycogen decreased (P < 0.05) by 51% and 23%, respectively. No significant differences were observed in muscle CP, lactate, pH, or glycogen between 90 and 100% of exhaustion time. During the precompetition period, elite soccer players improved (P < 0.05) Yo-Yo test performance and maximum oxygen uptake ([OV0312]O(2max)) by 25 +/- 6 and 7 +/- 1%, respectively. High-intensity running covered by the players during games was correlated to Yo-Yo test performance (r = 0.71, P < 0.05) but not to [OV0312]O(2max) and ITT performance. CONCLUSION The test had a high reproducibility and sensitivity, allowing for detailed analysis of the physical capacity of athletes in intermittent sports. Specifically, the Yo-Yo intermittent recovery test was a valid measure of fitness performance in soccer. During the test, the aerobic loading approached maximal values, and the anaerobic energy system was highly taxed. Additionally, the study suggests that fatigue during intense intermittent short-term exercise was unrelated to muscle CP, lactate, pH, and glycogen.

The Yo-Yo Intermittent Recovery Test A Useful Tool for Evaluation of Physical Performance in Intermittent Sports

The two Yo-Yo intermittent recovery (IR) tests evaluate an individual’s ability to repeatedly perform intense exercise. The Yo-Yo IR level 1 (Yo-Yo IR1) test focuses on the capacity to carry out intermittent exercise leading to a maximal activation of the aerobic system, whereas Yo-Yo IR level 2 (Yo-Yo IR2) determines an individual’s ability to recover from repeated exercise with a high contribution from the anaerobic system. Evaluations of elite athletes in various sports involving intermittent exercise showed that the higher the level of competition the better an athlete performs in the Yo-Yo IR tests. Performance in the Yo- Yo IR tests for young athletes increases with rising age. The Yo-Yo IR tests have shown to be a more sensitive measure of changes in performance than maximum oxygen uptake. The Yo-Yo IR tests provide a simple and valid way to obtain important information of an individual’s capacity to perform repeated intense exercise and to examine changes in performance.

Physical and metabolic demands of training and match-play in the elite football player

Abstract In soccer, the players perform intermittent work. Despite the players performing low-intensity activities for more than 70% of the game, heart rate and body temperature measurements suggest that the average oxygen uptake for elite soccer players is around 70% of maximum ([Vdot]O2max). This may be partly explained by the 150 – 250 brief intense actions a top-class player performs during a game, which also indicates that the rates of creatine phosphate (CP) utilization and glycolysis are frequently high during a game. Muscle glycogen is probably the most important substrate for energy production, and fatigue towards the end of a game may be related to depletion of glycogen in some muscle fibres. Blood free-fatty acids (FFAs) increase progressively during a game, partly compensating for the progressive lowering of muscle glycogen. Fatigue also occurs temporarily during matches, but it is still unclear what causes the reduced ability to perform maximally. There are major individual differences in the physical demands of players during a game related to physical capacity and tactical role in the team. These differences should be taken into account when planning the training and nutritional strategies of top-class players, who require a significant energy intake during a week.

High-intensity running in English FA Premier League soccer matches

Abstract The aims of this study were to (1) determine the activity profiles of a large sample of English FA Premier League soccer players and (2) examine high-intensity running during elite-standard soccer matches for players in various playing positions. Twenty-eight English FA Premier League games were analysed during the 2005–2006 competitive season (n = 370), using a multi-camera computerised tracking system. During a typical match, wide midfielders (3138 m, s = 565) covered a greater distance in high-intensity running than central midfielders (2825 m, s = 473, P = 0.04), full-backs (2605 m, s = 387, P < 0.01), attackers (2341 m, s = 575, P < 0.01), and central defenders (1834 m, s = 256, P < 0.01). In the last 15 min of a game, high-intensity running distance was ∼20% less than in the first 15-min period for wide midfielders (467 m, s = 104 vs. 589 m, s = 134, P < 0.01), central midfielders (429 m, s = 106 vs. 534 m, s = 99, P < 0.01), full-backs (389 m, s = 95 vs. 481 m, s = 114, P < 0.01), attackers (348 m, s = 105 vs. 438 m, s = 129, P < 0.01), and central defenders (276 m, s = 93 vs. 344 m, s = 80, P < 0.01). There was a similar distance deficit for high-intensity running with (148 m, s = 78 vs. 193 m, s = 96, P < 0.01) and without ball possession (229 m, s = 85 vs. 278 m, s = 97, P < 0.01) between the last 15-min and first 15-min period of the game. Mean recovery time between very high-intensity running bouts was 72 s (s = 28), with a 28% longer recovery time during the last 15 min than the first 15 min of the game (83 s, s = 26 vs. 65 s, s = 20, P < 0.01). The decline in high-intensity running immediately after the most intense 5-min period was more evident in attackers (216 m, s = 50 vs. 113 m, s = 47, P < 0.01) and central defenders (182 m, s = 26 vs. 96 m, s = 39, P < 0.01). The results suggest that high-intensity running with and without ball possession is reduced during various phases of elite-standard soccer matches and the activity profiles and fatigue patterns vary among playing positions. The current findings provide valuable information about the high-intensity running patterns of a large sample of elite-standard soccer players, which could be useful in the development and prescription of specific training regimes.

The Yo-Yo IR2 Test: Physiological Response, Reliability, and Application to Elite Soccer

PURPOSE To examine the physiological response, reliability, and validity of the Yo-Yo intermittent recovery level 2 test (Yo-Yo IR2). METHODS Thirteen normally trained male subjects carried out four Yo-Yo IR2 tests, an incremental treadmill test (ITT), and various sprint tests. Muscle biopsies and blood samples were obtained, and heart rate was measured before, during, and after the Yo-Yo IR2 test. Additionally, 119 Scandinavian elite soccer players carried out the Yo-Yo IR2 test on two to four occasions. RESULTS Yo-Yo IR2 performance was 591 +/- 43 (320-920) m or 4.3 (2.6-7.9) min. Test-retest coefficient of variation in distance covered was 9.6% (N = 29). Heart rate (HR) at exhaustion was 191 +/- 3 bpm, or 98 +/- 1% HRmax. Muscle lactate was 41.7 +/- 5.4 and 68.5 +/- 7.6 mmol x kg(-1) d.w. at 85 and 100% of exhaustion time, respectively, with corresponding muscle CP values of 40.4 +/- 5.2 and 29.4 +/- 4.7 mmol x kg(-1) d.w. Peak blood lactate was 13.6 +/- 0.5 mM. Yo-Yo IR2 performance was correlated to ITT performance (r = 0.74, P < 0.05) and VO2max (r = 0.56, P < 0.05) but not to 30- and 50-m sprint performance. Yo-Yo IR2 performance was better (P < 0.05) for international elite soccer players than for moderate elite players (1059 +/- 35 vs 771 +/- 26 m) and better (P < 0.05) for central defenders (N = 21), fullbacks (N = 20), and midfielders (N = 48) than for goalkeepers (N = 6) and attackers (N = 24). Fifteen elite soccer players improved (P < 0.05) Yo-Yo IR2 performance by 42 +/- 8% during 8 wk of preseasonal training. CONCLUSION This study demonstrates that the Yo-Yo IR2 test is reproducible and can be used to evaluate an athletes ability to perform intense intermittent exercise with a high rate of aerobic and anaerobic energy turnover. Specifically, the Yo-Yo IR2 test was shown to be a sensitive tool to differentiate between intermittent exercise performance of soccer players in different seasonal periods and at different competitive levels and playing positions.

Muscle temperature and sprint performance during soccer matches – beneficial effect of re‐warm‐up at half‐time

The relationship between quadriceps muscle temperature (Tm) and sprint performance was evaluated during soccer matches in 25 competitive players. In one game, Tm was determined frequently (n=9). In another game, eight players performed low‐intensity activities at half‐time (re‐warm‐up, (RW), whereas another eight players recovered passively (CON). Tm was 36.0±0.2 °C at rest and increased (P<0.05) to 39.4±0.2 °C before the game and remained unaltered during the first half. At half‐time, Tm decreased (P<0.05) to 37.4±0.2 °C, but increased (P<0.05) to 39.2±°C during the second half. In CON and RW, Tm and core temperature (Tc) were similar before and after the first half, but 2.1±0.1 and 0.9±0.1 °C higher (P<0.05), respectively, in RW prior to the second half. At the onset of the second half, the sprint performance was reduced (P<0.05) by 2.4% in CON, but unchanged in RW. The decrease in Tm was correlated to the decrease in performance (r=0.60, P<0.05, n=16). This study demonstrates that in soccer, the decline in Tm and Tc during half‐time is associated with a lowered sprint capacity at the onset of the second half, whereas sprint performance is maintained when low‐intensity activities preserve muscle temperature.

Application of four different football match analysis systems: a comparative study.

Abstract Using a video-based time–motion analysis system, a semi-automatic multiple-camera system, and two commercially available GPS systems (GPS-1; 5 Hz and GPS-2; 1 Hz), we compared activity pattern and fatigue development in the same football match. Twenty football players competing in the Spanish second and third divisions participated in the study. Total distance covered during the match for the four systems was as follows: 10.83 ± 0.77 km (semi-automatic multiple-camera system, n = 20), 9.51 ± 0.74 km (video-based time–motion analysis system, n = 17), 10.72 ± 0.70 km (GPS-1, n = 18), and 9.52 ± 0.89 km (GPS-2, n = 13). Distance covered by high-intensity running for the four systems was as follows: 2.65 ± 0.53 km (semi-automatic multiple-camera system), 1.61 ± 0.37 km (video-based time–motion analysing system), 2.03 ± 0.60 km (GPS-1), and 1.66 ± 0.44 km (GPS-2). Distance covered by sprinting for the four systems was as follows: 0.38 ± 0.18 km (semi-automatic multiple-camera system), 0.42 ± 0.17 km (video-based time–motion analysing system), 0.37 ± 0.19 km (GPS-1), and 0.23 ± 0.16 km (GPS-2). All four systems demonstrated greater (P < 0.05) total distance covered and high-intensity running in the first 15-min period and less (P < 0.05) total distance covered and high-intensity running during the last 15-min period than all other 15-min intervals, with a reduction (P < 0.05) in high-intensity running from the first to the last 15-min period of 46 ± 19%, 37 ± 26%, 50 ± 26%, and 45 ± 27% for the semi-automatic multiple-camera system, video-based time–motion analysis system, GPS-1, and GPS-2, respectively. Our results show that the four systems were able to detect similar performance decrements during a football game and can be used to study game-induced fatigue. Rather large between-system differences were present in the determination of the absolute distances covered, meaning that any comparisons of results between different match analysis systems should be done with caution.

Glucose ingestion attenuates interleukin-6 release from contracting skeletal muscle in humans

To examine whether glucose ingestion during exercise affects the release of interleukin‐6 (IL‐6) from the contracting limb, seven men performed 120 min of semi‐recumbent cycling on two occasions while ingesting either 250 ml of a 6.4 % carbohydrate (GLU trial) or sweet placebo (CON trial) beverage at the onset of, and at 15 min intervals throughout, exercise. Muscle biopsies obtained before and immediately after exercise were analysed for glycogen and IL‐6 mRNA expression. Blood samples were simultaneously obtained from a brachial artery and a femoral vein prior to and during exercise and leg blood flow was measured by thermodilution in the femoral vein. Net leg IL‐6 release, and net leg glucose and free fatty acid (FFA) uptake, were calculated from these measurements. The arterial IL‐6 concentration was lower (P < 0.05) after 120 min of exercise in GLU, but neither intramuscular glycogen nor IL‐6 mRNA were different when comparing GLU with CON. However, net leg IL‐6 release was attenuated (P < 0.05) in GLU compared with CON. This corresponded with an enhanced (P < 0.05) glucose uptake and a reduced (P < 0.05) FFA uptake in GLU. These results demonstrate that glucose ingestion during exercise attenuates leg IL‐6 release but does not decrease intramuscular expression of IL‐6 mRNA.

Exercise induces hepatosplanchnic release of heat shock protein 72 in humans

Physical exercise results in the appearance of heat shock protein (HSP) 72 in the circulation that precedes any increase in gene or protein expression in contracting skeletal muscle. In rodents, exercise increases liver HSP72 expression and the hepatosplanchnic viscera are known to release many acute phase proteins. In the present study, we tested the hypothesis that the splanchnic tissue beds release HSP72 during exercise. Seven male subjects performed 120 min of semi‐recumbent cycling at 62 ± 2 % of maximal oxygen uptake. Blood samples were obtained simultaneously from a brachial artery, a femoral vein and the hepatic vein prior to and at 30, 60 and 120 min of exercise. Leg blood flow (LBF) was measured by thermodilution in the femoral vein, and hepatosplanchnic blood flow (HBL) was measured using indocyanine green dye. Net leg and net hepatosplanchnic HSP72 balance were calculated as the product of LBF and femoral venous‐arterial HSP72 difference and the product of HBF and hepatic venous‐arterial HSP72 difference, respectively. Arterial plasma HSP72 was only detected in one subject at rest but progressively appeared in the arterial samples throughout exercise such that at 120 min it was detected in all subjects (0.88 ± 0.35 pg l−1; P < 0.05 compared with rest). The contracting muscle did not, however, contribute to this increase since there was no difference in the femoral venous‐arterial HSP72 concentration at any time. Rather, the increase in arterial HSP72 was accounted for, at least in part, by release from the hepatosplanchnic viscera with values increasing (P < 0.05) from undetectable levels at rest to 5.2 ± 0.2 pg min−1 after 120 min. These data demonstrate that the splanchnic tissues release HSP72 during exercise and this release is responsible, in part, for the elevated systemic concentration of this protein during exercise.