Heart rate (HR) is commonly used to monitor and to design aerobic training (Gilman, 1996). Recently, Hoff et al. (2002) have been shown that the relationship in soccer-specific exercises (five-a-side, dribbling track) was not significantly different from
relationship found in the laboratory. Using this relationship it is possible to analyze the metabolic demands and the energy cost of sport-specific exercises or competitions. Furthermore, HR itself was suggested to be indicative of physiological effort (Reilly, 1997). These findings support the use of HR in aerobic soccer training. In fact, aerobic endurance training, using interval training performed at a target HR (9095% of HRmax) improved soccer performance by increasing distance covered during a match, work intensity, the number of the sprints and involvements with the ball (Helgerud et al., 2001). In addition, Hoff et al. (2002), have shown that is possible to reach a similar exercise intensity as match-play by using games and a soccer-specific circuit track as in interval training.