Journal of Strength and Conditioning Research, 2005, 19(1), 79–84 q 2005 National Strength & Conditioning Association
COMPARATIVE STUDY OF FIELD AND LABORATORY TESTS FOR THE EVALUATION OF AEROBIC CAPACITY IN SOCCER PLAYERS THOMAS I. METAXAS, NIKOLAOS A. KOUTLIANOS, EVANGELIA J. KOUIDI, AND ASTERIOS P. DELIGIANNIS Laboratory of Sports Medicine, Department of Physical Education and Sport Science, Aristotle University of Thessaloniki, Thessaloniki, Greece.
ABSTRACT. Metaxas, T.I., N.A. Koutlianos, E.J. Kouidi, and A.P. Deligiannis. Comparative study of field and laboratory tests for the evaluation of aerobic capacity in soccer players. J. Strength Cond. Res. 19(1):79–84. 2005.—The purpose of this study was to ˙ O2max) values in soccer evaluate the maximal oxygen uptake (V players as assessed by field and laboratory tests. Thirty-five elite young soccer players were studied (mean age 18.1 6 1.0 years, training duration 8.3 6 1.5 years) in the middle of the playing season. All subjects performed 2 maximal field tests: the ˙ O2max accordYo-Yo endurance test (T1) for the estimation of V ing to normogram values, and the Yo-Yo intermittent endurance test (T2) using portable telemetric ergospirometry; as well as 2 maximal exercise tests on the treadmill with continuous (T3) and ˙ O2max values of the intermittent (T4) protocols. The estimated V T1 test (56.33 ml·kg21·min21) were 10.5%, 11.4%, and 13.3% (p # 0.05) lower than those of the T2 (62.96 ml·kg21·min21), T3 (63.59 ml·kg21·min21) and T4 (64.98 ml·kg21·min21) tests, respectively. Significant differences were also found between the intermittent exercise protocols T1 and T3 (p # 0.001) and the continuous exercise protocols T2 and T4 (p # 0.001). There was a ˙ O2max values of high degree of cross correlation between the V the 3 ergospirometric tests (T2 versus T3, r 5 0.47, p # 0.005; T2 versus T4, r 5 0.59, p # 0.001; T3 versus T4 r 5 0.79, p # 0.001). It is necessary to use ergospirometry to accurately estimate aerobic capacity in soccer players. Nevertheless, the Yo-Yo field tests should be used by coaches because they are easy and helpful tools in the training program setting and for player followup during the playing season. KEY WORDS. treadmill exercise tests, Yo-Yo field tests, estima˙ O2max tion, V
INTRODUCTION odern soccer demands both strong physical conditioning and technical characteristics (23). The improvement of aerobic and anaerobic capacity, muscle strength, speed, and neuromuscular coordination are the main targets of soccer training (46). Soccer players have to adapt to the requirements of the game in order to compete at the highest level. Therefore, aerobic capacity is an important skill for the evaluation of performance in soccer players (1, 42, 44). It is well known that physical conditioning and aerobic capacity in particular, depend on 3 important elements: maximal oxygen consumption ˙ O2max), anaerobic threshold, and work economy (24, (V 38). Soccer includes high-intensity, intermittent boats of exercise, which stresses the anaerobic glycolysis metabolic pathway (3, 12, 17, 25, 49). The contribution of anaerobic glycolysis to total metabolism in soccer has been ex-
M
amined in various studies mainly by determining the blood lactate concentration (7, 22, 50). The responses to intermittent activity are characterized by higher levels of physiological strain compared to that of continuous exercise performed at the same mean work rate (4, 13). The aerobic capacity of a soccer player is customarily evaluated via various field and laboratory tests. The majority of these tests are executed with protocols based on continuous types of exercise. However, a test is more reliable and effective when it is specific to the exercise patterns (27). Therefore, many European soccer teams use the Yo-Yo field test in daily practice (3, 4). The physiological responses to intermittent exercise have also been compared with those of continuous exercise at the same average workload in an attempt to evaluate differences between exercise patterns (2, 16, 18). The comparison of the 2 exercise patterns is interesting because both intermittent and continuous exercises are used in soccer training to facilitate physiological adaptations and to improve performance (43). Intermittent exercise is performed at the same average work rate as continuous exercise and has been associated with increased physiological strain (16). Other researchers have failed to note differences in the energy cost between intermittent and continuous exercises (2, 18). To date, no substantial information is available regarding the relative physiological cost of a single bout of soccer-specific intermittent exercise compared with that of a continuous one at the same average intensity using field and laboratory methods. Therefore, the purpose of this study was to compare 2 field tests (Yo-Yo continuous and intermittent endurance tests) with 2 laboratory treadmill exercise tests (continuous and intermittent) in the evaluation of maximal oxygen uptake in elite soccer players. The proposed hypothesis of the study is that there are no significant differences between the various exercise tests regarding maximal oxygen uptake determination.
METHODS Experimental Approach to the Problem
All soccer players performed 4 maximal exercise tests; 2 in the field and 2 in the laboratory for an evaluation of their aerobic capacity in the middle of the regular training season. (Table 1). The field tests were executed on a grass field. The tests were carried out randomly, and the time interval between them was at least 2 days. All tests 79
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TABLE 1. Experimental study design. Field tests Laboratory tests
T1 T2 T3 T4
Yo-Yo endurance test Yo-Yo intermittent endurance test Continuous incremental protocol Intermittent exercise protocol
and measurements were performed in the morning within a 15-day period. The test-retest reliability for all ergospirometric tests was 0.98. The temperature was 208C–228C, and the relative humidity was no more than 50% in the field as well as in the laboratory during the tests. Wind velocity on the field did not exceed 0.5 m·s 21. Subjects
Thirty-five elite soccer players participated in this study. Their mean age was 18.1 6 1.0 years, and they were all in training systematically for more than 6 years (mean training period 8.3 6 1.5 years). All players were members of the Greek National Soccer Team U-20 (under 20 years old). All subjects were nonsmokers and none used any ergogenic aid or medication known to affect cardiorespiratory function during the study. The protocol of this study was in accordance with the guidelines of the Ethical Committee of Aristotle University of Thessaloniki and the revised declaration of Helsinki. All participants gave their written consent. Anthropometric Measurements
All soccer players underwent a physical examination, anthropometric tests including body fat assessment with skinfold measurements (4-fold method) by specific caliper (Lafayette Instrument Co., Lafayette, Indiana), and resting electrocardiogram (Excel 106, Cardiette, Trento, Italy). Field Tests
The Yo-Yo endurance test—level 1 (T1) was used to evaluate the ability to run continuously for a long period of time. According to this test, the basic aim for the soccer player is to perform as many 20-meter distances as possible within the given time limit (4). When the participant stops, the last speed and the number of performed 20meter distances at this speed are recorded, including that ˙ O2max value was estimated according to of the last run. V the relative normogram of the running distance and associated oxygen consumption. The Yo-Yo intermittent endurance test—level 1 (T2) was also performed to evaluate the players’ ability to repeatedly perform during intervals over a prolonged period of time. Due to the lack of any indicative normograms for ˙ O2 uptake in this test, a portable telethe estimation of V metric device was used (Cosmed K2 Co., Rome, Italy). This telemetric device forms a direct measurement method of consumed O2 from the working muscles. Heart rate was recorded before, during, and after the tests using a Polar Sport Tester (Polar, Kempele, Finland). The players performed repeated 20-meter shuttle runs interspersed with a short recovery during which the players jogged until exhaustion (4). In this test, players had a 5-second rest between each shuttle. The subjects began to run forward 20 meters at the time of the first signal. The running speed had to be adjusted so that runners
Indirect method of aerobic performance valuation Portable direct ergospirometry Direct ergospirometry Direct ergospirometry
TABLE 2. Continuous treadmill protocol. Stage
Speed (km/h)
Grade (%)
Time (min)
1 2 3 4 5 6 7
8.0 10.0 12.0 14.0 16.0 18.0 20.0
1.0 1.0 1.0 2.0 2.0 2.0 2.0
3 3 3 3 3 3 3
TABLE 3. Intermittent treadmill protocol. Stage
Speed (km/h)
Grade (%)
Time (min)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
9.0 0.0 9.0 9.0 9.0 0.0 9.0 9.0 9.0 0.0 9.0 9.0 9.0 0.0 12.0 12.0 12.0 0.0 12.0
0.0 0.0 2.0 6.0 4.0 0.0 6.0 10.0 8.0 0.0 10.0 14.0 12.0 0.0 10.0 14.0 12.0 0.0 15.0
3 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
could reach the 20-meter marker exactly at the time of the next signal. Runners turned at the second marker and then returned to the first marker, which they had to reach by the time of the next signal. When the start marker was reached the subjects continued forward at a slower speed, ran around the cone that was positioned farther back from the start marker, and waited for the next signal. The actual time of this jog was exactly 5 seconds. The goal of the participants was to perform as many 2 3 20-meter intervals as possible within the given time limit. When each participant stopped, the last speed and the number of performed 2 3 20-meter intervals at this speed were recorded. The last 2 3 20-meter interval was included. Laboratory Tests
All soccer players performed 2 additional maximal exercise tests on a treadmill (TM 400 Trackmaster, Carrollton, TX) within 1 week after the end of the field tests. The first test used a continuous (T 3, Table 2) protocol, and the second test used an intermittent (T4, Table 3) protocol. Maximal oxygen uptake was measured during both
PERFORMANCE TESTING TABLE 4. Anthropometric characteristics of subjects. Variables Height (m) Weight (kg) Body surface area (m2) Lean body mass (kg) Body fat (%)
6 6 6 6 6
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RESULTS
(Mean 6 SD) 1.77 70.34 1.86 59.86 14.80
IN
0.06 5.61 0.09 4.32 2.62
tests via a breath-by-breath gas analyzing system (Quark b2, Cosmed Co., Rome, Italy). The following parameters were evaluated: resting heart rate (HR), systolic and diastolic blood pressures (sBP and dBP), maximum heart rate (HRmax), maximum systolic and diastolic blood pressures (sBPmax and dBPmax), exercise duration, maximal ˙ O2max), maximum ventilation (VEmax), oxygen uptake (V ˙ O2 ratio, and respiratory frequency (Rf). The the VE:V ˙ O2 measured, ˙ O2max was considered to be the highest V V when a plateau in O2 consumption was reported despite an increase in workload. Time to the point of exhaustion was recorded as the test result. Blood Analysis
Duplicated blood samples (10 ml each) were drawn from an ear lobe. The mean concentration of the 2 blood lactate values was determined at rest and in the 4th minute of recovery of each test using a lactate analyzer (Photometer LP 400, Dr. Lange). The reproducibility values for the Dr. Lange lactate analysis kit was 99.5%. Statistical Analyses
All results are reported as mean values and standard deviations (6 SD). A one-way analysis of variance for repeated measurements was used to determine differences among 4 exercise tests. Linear regression analysis was used to estimate the relationship between 2 variables. For statistical analysis, SPSS 11.5 for Windows was used (Statistical Package for the Social Sciences, Chicago, IL). In all cases the level of statistical significance was set at p # 0.05.
The anthropometric data and physical characteristics of all subjects are presented in Table 4. Time to the point of exhaustion was significantly higher in tests T2 and T4, which had intermittent workloads, compared with those of T1 and T3 (p # 0.05) (Table 5). However, the highest exercise time was noted in the treadmill intermittent exercise test. The T3 exercise test had a significantly greater duration by 6.3% (p # 0.05) compared with that of T1; moreover, the T4 had a higher exhaustion time by 10.4% (p # 0.05) compared with that of T2. In the T1 test, soccer players appeared to have the ˙ O2max in comparison to the other tests lowest value of V (p # 0.05). More specifically, the V˙ O2max in T1 was found to be lower by 10.5% (p # 0.05), 11.4% (p # 0.05), and 13.3% (p # 0.05) compared with those of the T2, T3, and T4 tests, respectively. Furthermore, a significant differ˙ O2max values between the ence was also found in the V intermittent exercise tests T1 and T3 (p # 0.001) and the ˙ O2max continuous tests T2 and T4 (p # 0.001). In T3 the V was higher by 2.2% (p # 0.05) compared with that of T4. ˙ O2max values of the 3 ergospirometric tests showed The V a high degree of cross correlation (T2 versus T3, r 5 0.47, p # 0.005; T2 versus T4, r 5 0.59, p # 0.001; T3 versus T4, r 5 0.79, p # 0.001) (Figures 1, 2, and 3). Maximum blood lactate levels in the T2 test were higher by 13.6% (p # 0.05) compared with those of the T1 test. Moreover, the maximum blood lactate levels in the T4 test were higher by 4.5% (p # 0.05) and by 8.8% (p # 0.05) than those of the T3 and T1 tests, respectively. There was no significant difference in maximum blood lactate levels between the T2 and T4 tests. Finally, there was no statistically significant differ˙ O2 between ˙ O2:HR, Rf, and VE:V ence in the HRmax, VE, V the 4 tests.
DISCUSSION The major finding of the present study is that the V˙ O2max measurement in soccer players using treadmill exercise
TABLE 5. Results of ergospirometric tests (mean 6 SD). Laboratory tests
Field tests Estimated Yo-Yo endurance test Resting heart rate (b·min21) Systolic blood pressure (mm Hg) Diastolic blood pressure (mm Hg) Lactate (mmol·l21) Time to exhaustion (min) Maximum heart rate (b·min21) Maximum systolic blood pressure (mm Hg) Maximum diastolic blood pressure (mm Hg) Ventilation (L·min21) ˙ O2 Ventilation V Respiratory frequency (b·min21) ˙ O2:heartrate (ml·b·min21) V ˙ O2max (ml·kg21·min21) V Lactate max (mmol·l21) † p # 0.05 versus T1 ‡ p # 0.05 versus T2 § p # 0.05 versus T3 \ p # 0.05 versus T4
62.1 120.2 78.5 1.78 13.28 197.3 174.0 72.2
6 6 6 6 6 6 6 6
7.1 7.6 6.0 0.3 0.8‡§\ 6.5 9.1 6.4
56.33 6 2.73‡§\ 9.93 6 1.74‡
Yo-Yo intermittent endurance test 62.8 121.1 79.4 1.50 15.68 196.3 172.0 74.4 135.1 30.8 55.3 22.6 62.96 11.28
6 6 6 6 6 6 6 6 6 6 6 6 6 6
8.1 6.7 6.4 0.39 2.87†§\ 9.4 8.2 6.2 19.5 5.7 10.1 2.8 3.78†\ 1.75†§
Continue protocol Intermittent protocol exercise test exercise test 61.3 118.3 77.1 1.66 14.12 196.7 176.6 70.9 142.8 29.5 55.9 26.8 63.59 10.33
6 6 6 6 6 6 6 6 6 6 6 6 6 6
6.9 10.4 6.2 0.45 1.96†‡\ 6.7 12.9 7.3 27.6 5.8 11.8 4.9 4.64†\ 2.01
62.7 117.9 77.0 1.81 17.31 194.9 173.7 70.9 145.9 32.3 59.8 27.9 64.98 10.80
6 6 6 6 6 6 6 6 6 6 6 6 6 6
7.1 7.3 5.4 0.45 2.62†‡§ 6.1 10.5 5.6 22.0 6.0 11.4 3.8 4.79†‡§ 1.90
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˙ O2max between T2 FIGURE 1. Linear regression analysis of V and T3 (r 5 0.47, p # 0.005).
˙ O2max between T2 FIGURE 2. Linear regression analysis of V and T4 (r 5 0.59, p # 0.001).
protocols is preferred over the Yo-Yo field tests. It seems that the Yo-Yo field tests with or without the telemetric method underestimated the measured maximal oxygen consumption values in contradiction to the performed hypothesis. In addition, these methods for measuring ˙ O2max should not be rejected because they can be easily V performed and are helpful in planning soccer training. The anthropometric data of our soccer players were similar to the corresponding results from previous studies in soccer (1, 14, 19, 37, 45, 48). However, the anthropometric characteristics from the teams of various countries and different leagues presented a wide range of results, especially in body weight (43). Anthropometric studies in soccer players have shown that height and body weight are important factors in the performance of these athletes (41, 43). It was also found that anthropometric characteristics are different depending on the position that each player on the team plays, as well as on the level of competition (professional vs. amateur) (30, 40, 52). It is a known fact that a high percentage of body fat reduces
˙ O2max between T3 FIGURE 3. Linear regression analysis of V and T4 (r 5 0.79, p # 0.001).
athletic performance. Some researchers found values of body fat at 9%–16% in high-level soccer players (44), whereas low vales (10.0%–11.5%) were observed in professional soccer players (28, 40). The range of percentage of body fat in our soccer players can be attributed to differences in training age. The aerobic capacity of our soccer players, which was indirectly estimated in the continuous field test (Yo-Yo endurance test), was in agreement with the values being reported for young elite soccer players that were obtained with the same method (4, 6, 7, 33, 34). Similar values of ˙ O2max were also observed by Metaxas et al. (2001) in V elite adult soccer players who performed the same Yo-Yo test (29). Furthermore, the Yo-Yo intermittent test has been proven to be a valid measure of physical performance in soccer with a high reproducibility (27). Nevertheless, the same authors observed that the Yo-Yo intermittent test performance was significantly correlated with the time to ˙ O2max values at the treadmill test, exhaustion and V which led to the assumption that the treadmill exercise tests do not underestimate aerobic performance in soccer. The results of this study are also in agreement with others, supporting the notion that a portable telemetric ergospirometer is a reliable method for determining an athlete’s aerobic capacity in the field (10, 11, 26, 39). It seems that this method can contribute effectively to creating the best training plan and lead to a higher level of sport performance in modern soccer. ˙ O2max in the Yo-Yo continuous The lower values of V test compared with those in the Yo-Yo intermittent test are possibly due to various factors such as the turn in the shuttle run, as well as the unstable running rate. Another possible cause is the effect of the acceleration immediately after the signal and turn. Regardless of these limiting ˙ O2max values, it should factors on the achievement of V be noted that the attainment of the estimated maximal heart rate ensured that players reached their exhaustion levels. Moreover, encouragement and competition between players during the test contributed to this finding (31). ˙ O2max determination in the laboraRegarding the V
PERFORMANCE TESTING
tory, higher values were observed in both continuous and intermittent tests in comparison to the corresponding field tests. This difference can be explained partly by the different running conditions, considering that in the field the turns in the shuttle run are a suspending factor in ˙ O2. It is also supported by the attainment of maximum V intermittent workload protocols that demonstrate higher ˙ O2max in comparison with constant protocols values of V (5, 15, 35, 36). Indeed, our soccer players reached their ˙ O2max during the intermittent test in highest values of V the laboratory. These findings are the result of using the constant protocols, which cause higher local muscle exhaustion, whereas in the intermittent protocol, the recovery phase contributes to the production of higher muscle workload (1, 17, 40, 52). The greater muscle exhaustion in the tests in which the constant workload protocol was used is due to the higher absolute time of exercise compared with the interval tests, in which the breaks for recovery are deleted. However, during the field and laboratory tests there was no significant difference in maximal heart rate. This ensures that all athletes achieved a maximum effort in all trials. The high level of blood lactate in all participants is ˙ O2max and demalso a criterion for the attainment of V onstrates the use of anaerobic energy production during exercise (24). The greatest values, which were noted during the interval attempts, are the results of high energy anaerobic adaptations of high-intensity efforts (7, 20, 42, 51). At the end of the Yo-Yo endurance test our soccer players recorded a significantly lower blood lactate concentration in comparison with the relative values measured both in the Yo-Yo intermittent recovery test and the laboratory tests. This is due to the lowest maximal workload that the soccer players strived for at the last stage. The explanation for this lies in the running velocity at the last stage between tests in which the constant workload protocol was applied (30, 47). Reduced maximal velocity must be due to maximal local muscle fatigue caused by the shuttle run during the field tests in comparison with the tests conducted in the laboratory, which had both a constant and intermittent progressively increasing workload (13). Blood lactate concentration seems to be independent of a soccer player’s aerobic capacity, because no significant correlation was found between the maximum blood ˙ O2max or the distance covered by athlactate values and V letes in the T1 test. A comparative study by Metaxas et al. (2000) on the cardiorespiratory adaptations of Greek professional and amateur soccer players showed that professionals had higher levels of adaptation (30). This could be due to the type and intensity of exercises applied in the different training models (32, 42). It was suggested that the level of aerobic capacity in Greek soccer players was significantly higher than in Portuguese (21), British (8), English (14), and Asian (9) players of the same age. This difference may also be the result of the aerobic targeted training problems that are applied by Greek coaches even to adolescent soccer players.
PRACTICAL APPLICATIONS ˙ O2max in soccer In conclusion, the determination of V players using treadmill exercise tests seems to be a more accurate method in comparison with field Yo-Yo tests. Thus, the evaluation of aerobic capacity with laboratory
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tests constituted an appropriate process of cardiorespiratory index analysis in soccer players. However, deter˙ O2max via telemetric method in the field is mining the V also useful for the evaluation of cardiorespiratory efficiency. Finally, the Yo-Yo field tests should be considered as an easy and helpful tool for trainers and should be applied for players’ follow-up during the playing season.
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Address correspondence to Dr. Thomas Metaxas, tommet@ phed.auth.gr.
