320 Journal of Strength and Conditioning Research, 2006, 20(2), 320–325  2006 National Strength & Conditioning Association AEROBIC FITNESS AND YO-YO CONTINUOUS AND INTERMITTENT TESTS PERFORMANCES IN SOCCER PLAYERS:ACORRELATION STUDY CARLO CASTAGNA, 1 FRANCO M. IMPELLIZZERI, 2 KARIM CHAMARI, 3 DOMENICO CARLOMAGNO, 2 AND ERMANNO RAMPININI 2 1 School of Sport and Exercise Sciences, Faculty of Medicine and Surgery, University of Rome Tor Vergata, Rome, Italy; 2 Human Performance Lab, S.S. MAPEI, Castellanza, Varese, Italy; 3 Unite ´ de Recherche, ‘‘Evaluation, Sport, Sante ´,’’ National Center of Medicine and Science in Sports, El Menzah, Tunisia. ABSTRACT. Castagna, C., F.M. Impellizzeri, K. Chamari, D. Car- lomagno, and E. Rampinini. Aerobic fitness and yo-yo continu- ous and intermittent tests performances in soccer players: A cor- relation study. J. Strength Cond. Res. 20(2):320–325. 2006.—Yo- yo tests are very popular in soccer; however, no study has ad- dressed details of their relation to canonical aspects of aerobic fitness. Furthermore, no information is available on the effect of the individual levels of lower limbs’ explosive strength on yo-yo tests in soccer players. The purpose of this study was to examine the physiological determinants of Yo-yo Endurance Test Level 2 (YYETL2) and Yo-yo Intermittent Recovery Test Level 1 (YYIRTL1) in soccer players. Twenty-four soccer players (body mass, 74.6  8.5 kg; height, 178.1  4.5 cm; age, 25.6  5.1 years) were tested for V ˙ O 2 max and ventilatory threshold (VT) on a motorized treadmill. Lower-limb explosive strength was as- sessed using vertical countermovement jumps (CMJ) performed on a force platform. Results showed that YYETL2 and YYIRTL1 performances (m) were significantly related ( r = 0.75, p = 0.00002). YYETL2 results were significantly related to V ˙ O 2 max, VTV ˙ O 2 , and speed at VT (r = 0.75, 0.76, and 0.83, respectively; p  0.00002). Peak treadmill speed results were significantly related to YYETL2 and YYIRTL1 (r = 0.87 and 0.71, respec- tively; p  0.0003). YYIRTL1 was related to CMJ peak power (r = 0.57; p = 0.003). These findings show that YYETL2 and YYIRTL1, although adopting similar starting and progression speeds, are influenced by different physiological variables. From these results, YYETL2 can be considered an aerobic fitness–re- lated field test, whereas YYIRTL1 can be regarded as an aero- bic–anaerobic, soccer-specific field test. KEY WORDS. field testing, shuttle running, intermittent exercise, association football INTRODUCTION C ompetitive soccer is an intermittent, high-inten- sity physical activity that requires well-devel- oped aerobic and anaerobic fitness (15, 32–34). The relevance of aerobic fitness in soccer has been confirmed by descriptive (36), cross-sectional (39), and training studies (18). Furthermore, as soccer perfor- mance is characterized by several actions, such as sprint- ing, jumping, changes in direction, and tackling, muscu- lar strength and power has also been shown to be impor- tant characteristics for soccer players (39). Aerobic fitness (maximum oxygen uptake, lactate thresholds, and running economy; 30) can be accurately evaluated using a variety of laboratory protocols during treadmill-running until exhaustion. Although the values obtained with laboratory testing are considered the gold standard for the measurement of aerobic fitness, the pro- cedures involved are time consuming and require trained personnel and expensive equipment. For these reasons, some field tests have been proposed as practical alter- natives to laboratory assessments, and they are common- ly used by coaches and applied sport scientists to evaluate aerobic training outcome in soccer players (12, 23). By far, the most popular tests for aerobic power (V ˙ O 2 max) are the 20-m shuttle run test (20MSRT; 23, 24) and the multi- stage fitness test (MSFT; 31). The latter being a modified version of the 20MSRT originally devised by Leger et al. (23, 24). More recently, Bangsbo (2, 3) suggested, for well- trained subjects, the Yo-yo Endurance Test Level 2 (YYETL2). Different from the MSFT and the 20MSRT that start at 8 and 8.5 km·h -1 , respectively, the YYETL2 uses an initial speed of 11.5 km·h -1 . The use of YYETL2 has been suggested with the aim of estimating V ˙ O 2 max in well-trained players in the attempt to shorten assess- ment-session time (2, 3). In field settings, however, the use of sport-specific en- durance tests as performance measures of tasks repro- ducing technical skills, movement patterns, and physio- logical demands of the competitive match-play is wide- spread (1, 4, 9, 10, 13–15, 21, 27, 35). The relevance of these specific endurance tests are commonly based on their logical validity. To date, only the Yo-yo Intermittent Recovery Test Level 1 (YYIRTL1) proposed by Bangsbo (2) has been both externally and internally validated (20, 21, 26). Starting at a speed similar to that used for YYETL2 (see Tables 1 and 2), YYIRTL1 consists of 2  20-m bouts of progressive speed shuttle-running, inter- spersed by 10 seconds of active recovery, performed until exhaustion following prerecorded acoustic signals (2). Re- cently, Krustrup et al. (21), using muscle biopsy and blood analysis, have shown that YYIRTL1 elicits maximal aer- obic responses while significantly stressing the anaerobic energy system. This confirms that the physiological de- mands involved during this soccer-specific endurance test are similar to those taxed during a soccer-match (1). For these reasons, both the shuttle run tests (20MSRT and MSFT), as indirect measures of V ˙ O 2 max, and the YYIRTL1, as an indicator of soccer-specific endurance, are commonly used by coaches as practical measures of training outcomes (20, 21). Match analysis has provided evidence that during competitive soccer, players perform a great deal of activ-