2a) Vertical momentum of trunk (Fig. 2b) Horizontal Paclitaxel momentum of upper limbs (Fig. 2c) Vertical momentum of upper limbs (Fig. 2d) Horizontal momentum of lower limbs Figure 3. Take-off and segmental angles during impulse in the back somersault (Fig. 3a) Round-off, flic-flac, salto backward stretched (RFS) (Fig. 3b) Round-off, salto-tempo, salto backward stretched (RTS) Acknowledgments We thank Mr. Mourad Hambli, Mr. Mokhtar Chtara and Mr. Habib Bouall��gue for their help in the experiment. This research was performed in collaboration with the National Centre of Medicine and Science in Sport, Tunisia..
Physical fitness is nowadays considered as one of the most important health markers in childhood ( Ortega et al., 2008 ).

Consequently, in the last decades several countries have been promoting physical fitness improvement among young people in different ways ( Department of Health and Human Services, 1990 ). In many circumstances, schools have been considered the best setting in which children with low fitness levels can be identified and a healthy lifestyle can be promoted ( Ortega et al., 2008 ). Therefore, one of the main Spanish government strategies was focused on modifying school legislations in order to give health a more important role in the Educational System ( Ministerio de Educaci��n y Ciencia, 2006 ). Schools are mainly attempting to increase the pupils�� health level by using measures such as the improvement of their physical fitness through physical education (PE) ( Ministerio de Educaci��n y Ciencia, 2006 ).

It has been concluded that the health promotion policies and physical activity programs should be designed to improve physical fitness, where strength and cardiovascular endurance are the most important health-related physical fitness components ( Ortega et al., 2008 ). It is known that planning long-term fitness programs is the best way to improve these components ( Donnelly et al., 2009 ). Nonetheless, in the PE setting these programs cannot last the whole course or a large part of it since many curricular contents must be developed in a school year ( Ministerio de Educaci��n y Ciencia, 2006 ). Consequently, in the PE setting we need to find short-term programs that could be also effective for the increment of fitness. One of the methodologies that meet these criteria could be the circuit training ( Dorgo et al.

, 2009 ; Granacher et al., 2011a ; Granacher et al., 2011b ). The circuit training effectively reduces the time devoted Brefeldin_A to training while allowing an adequate training volume to be achieved ( Alcaraz Ram��n et al., 2008 ). Moreover, it permits a greater motor engagement time ( Lozano et al., 2009 ), which is a very important requirement for the success of a PE program. In addition, this methodology has multilevel effects on fitness, especially in beginners ( Alcaraz Ram��n et al., 2008 ; Dorgo et al., 2009 ; Wong et al., 2008 ).