The average power with the full squat with 70kg also showed significant positive correlations with the sprint times. The CMJ height has been greatly used to access lower body power in soccer players (Wisloff, 1998; Helgerud, 2001; N��?ez, 2008; Ronnestad, 2008). Nevertheless, to our knowledge, only two previous studies done (Gorostiaga, 2004; L��pez-Segovia, 2010) have used loaded countermovement jump (CMJL) exercise for testing lower limb power in this population. Unfortunately, these authors (Gorostiaga, 2004; L��pez-Segovia, 2010) did not include sprint evaluations in their studies. Different factors such as lower reliability of testing at very short distances, the static start position in the sprint test and the location of the first photoelectric cells (30 cm behind start in these two studies) could explain the lack relationship reported between CMJ and time at 10m.

Although, the relationship obtained between the vertical jump and 30m sprint time (present study: r= ?0.55; p<0.05 vs. r= ?0.60; p<0.01) was similar to the study of Wisloff (2004), the relationships observed between the vertical jump and last running meters are consistent with the results perceived with loaded jump, given a similarity of muscle action in both types of jumps. Significant association between peak power during loaded CMJ and later stages of the sprint (r=?0.544 to ?0.611; p��0.05) were obtained. The T10�C30 and T20�C30 were significantly related with peak power observed in the CMJL exercise with 20, 30, and 40kg external load.

Cronin and Hansen (2005) observed similar results in professional rugby players between loaded (30kg) vertical jump height and 5m, 10m, and 15m sprint times. The higher relationships (R2= 41�C62%) observed in the present study were perceived with the longer distances rather than the initial run. As running velocity approaches maximum, those strength measures that require force to be produced at high velocities have been reported to be significantly related to sprint performance (Wilson, 1995; Young, 1995; Nesser, 1996). Wilson (1995) reported a significant relationship between force at 30 ms in a concentric squat jump and 30m sprint time (r= 0.62). Nesser (1996) claimed significant correlations between 40m sprint time and peak isokinetic torque at a velocity of 7.85 rad/s for the hip and knee extensors and knee flexors (r= 0.54 to 0.61).

We agree with the assertion that results show a slight tendency of increased relationships such as velocity and distance increased (Table 2). Moreover, data showed that power output during the vertical jump with 20kg best explained sprint performance. This parameter was also significantly correlated with all split speed measurements, including the first sprint stages. Although correlations do not signify causation, CMJ training with light loads could be important Batimastat to improve sprint performance in soccer player��s under-21.