Exposure to altitude has detrimental effects on the human body and consequently on exercise performance. Namely, it has been shown that the reduction in oxygen partial pressure in the atmospheric air reduces oxygen availability to the mitochondria, compromises adenosine triphosphate (ATP) production via oxidative phosphorylation, and thus reduces maximal oxygen uptake (V[Combining Dot Above]O2max) and endurance performance (3,6,9). Indeed, a number of laboratory studies show a reduction in V[Combining Dot Above]O2max and aerobic performance at altitude compared with sea level (3,6). This decline in V[Combining Dot Above]O2max has been recorded at altitudes as low as 580 m (6).
Aside from the aforementioned aerobic responses, the reduced air density at altitude facilitates sprint performance and alters the aerodynamics of flying objects (9). For instance, in the Mexico City Olympic Games held at an altitude of 2,240 m in 1968, a number of world records were set in sprinting events because of the reduced air resistance. A theoretical analysis, based on mathematical modeling, showed a reduction in performance from the 800 m to marathon events with increase in altitude (12). Regarding flying ball characteristics, it has been suggested that reduced air density at altitude would affect drag and lift forces acting on the ball, thus altering flight characteristics (9). This, in turn, might affect player's technical skills (9).
Most research articles have addressed individual athletes in specific sports, and thus findings cannot always be generalized in team sports such as football. In team sports, only 2 articles have examined the effect of altitude on performance. Hamlin et al. (8) tested rugby players at sea level and 12 hours after arrival at an altitude of 1,550 m. Players were tested for endurance (modified 20-m shuttle run test), repeated sprint ability (6 × 70 m agility test with a 30-second rest), single sprint, and rugby-specific fitness test. Analysis showed a significant decline in endurance performance measurements only (8).
In another study, McSharry (11) and Gore et al. (7) analyzed 1,460 football matches to assess the effect of altitude on results. After normalizing the number of goals scored and goals conceded for each game relative to the mean number of goals scored and goals conceded for each team (7), they concluded that (a) sea-level teams playing against teams that are residents of moderate/high altitude have a low probability to win when playing away, and (b) teams that are residents of moderate/high altitude showed low probability to win at sea level. The first finding further evidences the detrimental effect altitude can have on performance. The latter finding indicates that altitude-induced changes in ball's flight characteristics might diminish neuromuscular coordination of high-altitude resident players when competing at sea level. This, in turn, might explain their low probability to win at sea level (9).
Hosted in South Africa, the Fédération Internationale de Football Association (FIFA) 2010 World Cup matches were played at altitudes ranging from 0 m (Durban) to 1,753 m (Johannesburg). Theoretically, altitudes above 580 m would have negatively affected endurance performance during matches (6). In addition, technical skills could have been altered at altitude because a reduced air density might affect flying ball characteristics and goalkeepers' reactions (9).
Therefore, the aim of the present study was to examine the effect of altitude on football performance using match analysis data from the 2010 World Cup.
Experimental Approach to the Problem
Certain physical and technical data collected during the 2010 World Cup matches were used in this analysis. Physical characteristics included total distance covered, distance covered in team's ball possession, distance covered without team's ball possession, and top running speed. Number of goals scored and goals conceded due to goalkeepers' error were included in the analysis as indices of technical performance.
Outfield players were included in the physical analysis, and goalkeepers were only included in the technical analysis. Players dismissed with a red card before 75 minutes of elapsed match time were also excluded from further analysis. Because of the nature of the study, no informed consents were collected from the players. The study was approved by a university-based ethics committee.
The FIFA 2010 World Cup was staged in South Africa from June 11 to July 11, 2010. Sixty-four games were played at 9 cities of varying altitudes. These cities and the corresponding altitudes were Cape Town (0 m), Durban (0 m), Port Elizabeth (0 m), Nelspruit (660 m), Polokwane (1,312 m), Pretoria (1,370 m), Bloemfontein (1,400 m), Rustenburg (1,500 m), and Johannesburg (1,753 m). Eight games were played in Cape Town, 7 in Durban, 8 in Port Elizabeth, 4 in Nelspruit, 4 in Polokwane, 6 in Pretoria, 6 in Bloemfontein, 6 in Rustenburg, and 15 in Johannesburg. Of the 64 matches, 48 were played in group stage and 16 in stage 2 (round of 16, quarter finals, semifinals, third and fourth places, and finals).
One hundred twenty-eight teams were available for the physical performance analysis (64 matches × 2). For various reasons (explained below and in Table 2), 23 teams were not included in the analysis. Thus, data from 105 teams were analyzed (Table 1). The distribution of teams included in the analysis and those not included are presented in Tables 1 and 2, respectively. Teams not included were those in which a player was dismissed with a red card before the 75th minute and those that played extra time (only in stage 2 matches).
Data were grouped according to altitude as sea level (0 m, n = 39 teams), at 660 m (n = 8 teams), 1200–1400 m (n = 25 teams), and 1401–1753 m (n = 33 teams). All physical and technical characteristics were analyzed per team. Data were recorded from the official FIFA website (http://www.fifa.com/worldcup/statistics/players/distanceandspeed.html, during the World Cup, and www.fifa.com/worldcup/archive/southafrica2010/statistics/index.html, after the World Cup).
It was hypothesized that (a) total distance covered, an index of endurance, would be reduced starting at an altitude of 660 m, and (b) technical skills would be affected because altitude alters ball flight characteristics.
The normality of distribution was checked for all variables with the Kolmogorov-Smirnov test. All variables were normally distributed. Differences between match play locations were assessed with a one-way analysis of variance (ANOVA) with 4 levels (corresponding to the 4 altitude levels). Where a significant difference was found with ANOVA, a Fisher's Least Significant Difference post hoc test was employed. A p value of <0.05 was used as a criterion of statistical significance. Statistical analyses were completed with SPSS (version 13.0; SPSS 13.0, Armonk, NY, USA). Values are presented as mean ± SD in tables and mean ± SE in figures and in text.
Total distances covered during matches played above 1200 m were significantly lower than those at sea level (106.9 ± 4.3 km at sea level, 105.9 ± 10.5 km at 660 m, 103.5 ± 5.4 km at 1200–1400 m, and 103.6 ± 5.2 km at 1401–1753 m; p < 0.05; Figure 1). No difference was found between 660 m and at sea-level performance. However, distances covered both with and without ball possession, and top running speed, did not differ between the game locations (Table 3). Also, no differences were found in the number of goals scored and goalkeeper errors that resulted in goals conceded between the match locations (Table 3).
The main finding of this study was that the teams' endurance performance, determined by the total distance covered during the game, was 3.1% lower in the matches played at altitudes above 1,200 m during the 2010 World Cup compared with sea-level values. However, it is noteworthy that the maximal speed, the number of goals scored, and the errors made by the goalkeepers that resulted in goals conceded were not significantly influenced by altitude. This is the first study to show the effect of altitude on football performance using physical and technical data from official matches.
The negative effects of hypoxia on exercise performance have been shown in a number of laboratory studies (3,4,6,15). Namely, in endurance athletes, V[Combining Dot Above]O2max declines approximately 0.5–1% for every 100 m altitude above sea level (15), and this drop is observed at altitudes as low as 580 m (6,14). In this study, the critical altitude was detected at an ascent above 1,200 m, which is in contradiction to the laboratory studies. In particular, the total distance covered by the players during the matches at that altitude (1,200 m) was almost 3.1% lower compared with that in the sea-level matches in this study. Of course, no direct comparison of the present findings with the aforementioned studies can be made because football is a more complex activity than an endurance run, and it involves repeated bouts of low to maximal exercise for a period of at least 90 minutes.
There is a lack of information regarding the effect altitude may have on performance in team sports. In the single experimental study, Hamlin et al. (8) reported a 3.4% decline in the endurance performance (modified 20-m shuttle run test) for rugby players tested at an altitude of 1,550 m, an almost similar result to this study.
The 3.1% drop in endurance performance with altitude in this study could be because of a reduction in V[Combining Dot Above]O2max resulting in a higher relative exercise intensity at any given absolute rate of movement. This in turn might have led to a higher perception of effort and fatigue than at sea-level work (6). The diminished V[Combining Dot Above]O2max was probably because of the lower oxygen partial pressure at altitude that resulted in lower ATP production via mitochondrial oxidative phosphorylation (5,9). It is of note that the detrimental effect of hypoxia on aerobic performance is greater in well-trained athletes than in untrained individuals, and this should be taken into account when applying these findings to other populations. The greater V[Combining Dot Above]O2max reduction in well-trained athletes is attributed to the diminished diffusion capacity of the lung in these athletes compared with untrained individuals (13).
Maximal running speed was not affected by altitude during the World Cup 2010. Similar results have been reported by Hamlin et al. (8). In their study, sprint times in single straight-line sprints did not differ when rugby players were tested at 1,550 m and at sea level (8). This was unexpected because the lower air density at altitude should facilitate sprint performance. Indeed, a previous study has shown an almost 1% improvement in 100 m performance at 1,500 m of altitude (12). However, sprint distances in football game average only 6–8 m (2), and football players rarely achieve their maximum speed in games because they usually do not run in a straight line. These factors may explain the absence of sprint time difference with altitude in the 2010 World Cup.
Previous research attributed the improvement in sprint time experienced at altitude to the lower air density (12). Reduced air density could also, theoretically, affect ball aerodynamics, flight characteristics, and consequently the players' technical skills (9). Indeed, the 2 forces acting on a flying ball, drag and lift, are directly proportional to air density. Air density reduces about 3% for every 305 m increase in altitude (9), which means a reduction of approximately 6% at 660 m, approximately 12% at 1,200 m, and approximately 15–18% at 1,753 m. In practical terms, this means that the ball would project further and curve less at altitude, which might change the ability to score a goal and for goalkeepers to follow and anticipate the flight of the ball. However, neither the number of goals scored nor the number of goals conceded because of goalkeepers' errors were affected by altitude at the World Cup 2010 games. This could be because of the teams' acclimatization in altitude, although no such data are available in this study and supporting evidence is lacking in the literature.
Indeed, pretournament altitude acclimatization could have impacted teams' physical and technical performance, which might have affected these results. To the author's knowledge, the effect of acclimatization period on team sports performance is unclear. Although the recommendation is clear for playing games at elevations above 2,000 m, it is not the same for lower altitudes (7). Hamlin et al. (8) showed that pre-acclimatization via intermittent hypoxic exposure (breathing hypoxic gas for 60 minutes per day for about 2 weeks) had an unclear effect on endurance, single, and multiple sprints performance at an altitude of 1,550 m (8). The recommendation, based on the consensus statement on playing football at different altitudes is that football players “would likely benefit from several days of acclimatization in situ” when playing at altitudes as high as 1,700 m (1,7).
A wide interindividual variability in the level of V[Combining Dot Above]O2max reduction at a certain hypoxia and hence altitude has been reported (10), and this should also be taken into account when applying these data to other teams or players. For instance, Hamlin et al. (8) reported a variation in endurance performance decline from −0.2 to −6.5% within 12 hours of testing at 1,550 m. Genetic variation might also explain individual differences in performance at altitude (10). Finally, one must remember that performance in football is multifactorial requiring a mixture of physical, technical, and tactical aspects. A number of these factors were not evaluated in this study, and this should be taken into account when interpreting these results.
Playing football at altitude above 1,200 m might decrease endurance performance but has no effect on certain technical aspects. To avoid physical performance decline that might decide match results when teams of almost similar technical and tactical quality compete, coaches should plan several days of acclimatization before playing official matches at altitudes. Thus, teams should not fly to altitudes of 1,500–1,700 m just 1–2 days before a football match, as is common practice, but should acclimatize for several days as suggested by the literature.
No funding was available. No competing interest to declare. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association. The author wishes to thank Dr. Michail Keramidas for his valuable comments on the revised manuscript.
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