Franco M. Impellizzeri, Piero Mognoni, Aldo Sassi, and Ermanno Rampinini
Introduction: Several studies have been highlighted the importance of training aerobic capacity in order to optimise or improve soccer performance (1). Indeed, VO2MAX has been shown to be related to team level, ranking and distance covered during a match (2, 3). Consequently, several field and laboratory tests have been proposed to evaluate players’ aerobic fitness. Usually, physiological assessments like VO2MAX, or field tests like shuttle-run, require maximal effort and they are commonly used to monitor longitudinal changes. However, maximal tests can be strongly influenced by athletes’ motivation and they are usually not well accepted by the subjects.In 1993 a submaximal test for soccer players was proposed in Italy (4). The test consist in a single run of 6 min duration at 13.5 km·h-1. In this study, the final [La-] was linearly related to OBLA velocity (r2= 0.91) measured in the same subjects during an incremental test. Consequently, they proposed a regression equation to estimate OBLA velocity. This submaximal constant speed test is commonly used in Italy to test players of various levels. The reason of the widespread of this procedure is probably due to its submaximal nature, quick execution and well acceptance by the athletes.We think that OBLA estimation is not necessary, but [La-] at the end of the 6 min run at 13.5 km·h-1 could be itself a useful index to monitor aerobic capacity changes in soccer players. Thus, the aim of this study was to validate this proposition, correlating the percent change in this test with the percent change in lactate threshold(LT)s measured in laboratory, after 8 weeks of soccer-training and official games.
Materials and Methods: Sixteen soccer young players (mean SD: age 17.5 0.6 yrs, weight 70.2 5.0 kg, height 178.5 4.8 cm), after having signed an informed consent to participate, performed an incremental test on a treadmill and a field test, before (T1) and after (T2) the first 8 weeks of the soccer season. The laboratory test protocol was similar to the one already used by Helgerud et al. (1), that is 1 km·h-1 increment every 5 min, at a treadmill inclination of 3%. Respiratory gases were measured breath by breath with a metabolic cart (VMAX29, Sensormedics, CA), while capillary blood lactate were collected from ear lobe at the end of each step, and immediately analysed (YSI® 1500 Sport, Yellow Springs, OH). From blood [La-] LT (1.5 mmol·L-1 above baseline)(1) and OBLA (4 mmol·L-1) were determined. Within one week the players performed the field test running on a track at 13.5 km·-1 for 6 min. At the end of the run [La-] ([La-]FIELD) were measured with the same analyser used in lab setting. The relationships between LTs (VO2 and velocity) and [La-]]FIELD, and between percent change of LTs and percent change of [La-]FIELD between the first and the second test, were examined using Pearson’s product moment correlations (r).
Results: Significant correlations were found between [La-]]FIELD and VO2·BM-1 at LT and OBLA in both tests (-0.62 < r < -0.83). Similarly, significant correlations were found between [La-]]FIELD and velocity at LT and OBLA (-0.62 < r < -0.76). The correlations between [La-]]FIELD, and VO2PEAK were not significant.The percent change (between T1 and T2) of the velocity at LT and OBLA was significantly correlated to the percent change of [La-]]FIELD (r = -0.60 and r = -0.54, respectively; p<0.05).
Discussion: Our results confirm previous study (1) in which a significant correlation between OBLA velocity and [La-] at the end of the 6 min run were found. In addition, after 8 weeks of training, we have found a significant correlation between changes in this simple physiological field test and LTs measured in the laboratory. These results suggest that this submaximal test can be use to monitor changes of aerobic capacity in alternative to maximal tests. The lowering of [La-] during submaximal workload should reflect a diminished production and an increase of the clearance capacity of the muscles, as a consequence of increased aerobic capacity (5). As lactate production could be also influenced by diminished glycogen stores due to previous hard training or overtraining., in absence of a maximal lactate value, we suggest to use also the [LA-]:RPE ratio that seems to decrease in overreached athletes (6). Despite we think that maximal and laboratory tests remain the best way to evaluate athletes, even with some limitation, the use of this kind of submaximal test could be a way to test soccer players more frequently and with results not influenced by motivation. To better evaluate the individual minimun detectable change of the [La-] measured during this test, specific reliability-studies are necessary.
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