Background: Young soccer players' injuries are receiving increased interest. The need of adopting injury prevention strategies to reduce financial, social and sport costs is obligated. The main purpose of this study is to analyse clinical characteristics of young soccer players in order to develop specific and effective injury prevention programs. Methods: This observational, transversal study includes 25 young soccer players from Spanish National League. Strength, motor control, flexibility and range of motion characteristics were analysed before the first preseason training. Results: Statistically significant differences were found for hip internal rotation (p value = 0.001), Thomas test (p value = 0.012) and ankle dorsiflexion test (p value = 0.009) between both sides. Dorsiflexion test showed a positive correlation with the hip internal rotation ROM (p < 0.016) and with the triple hop test (p < 0.007). The hip internal rotation ROM showed a positive correlation with the Thomas test (p < 0.033) and with the single leg squat test (p < 0.008). The drop jump test showed a positive correlation with the single leg squat test (p < 0.039). Conclusions: Clinical characteristics shown in this study should be taken into account in order to develop specific injury prevention for this specific population. Moreover, data shown in this study can be used as norm values for young soccer semi-professional players in future researches.

The rotation stress test is used to evaluate stability of the craniocervical junction by assuming that it gives the maximum rotation. However, a more complex manipulation might show a higher rotation: the rotation with extension and contralateral bending. This was tested in vitro with ten upper cervical spine specimens.

Instability is a serious and life-threatening diagnosis in the upper cervical spine (occiput-atlas-axis), and a depth understanding of normal range of movement is required for clinical manual evaluation. To improve this knowledge, ten upper cervical spine specimens have been tested in flexion, extension, lateral bending, and axial rotation.