Background: Over the past few decades, CrossFit has become a very popular physical activity. However, there is little literature on its effect, as resistance training, on the performance of soccer players. Objective: This study examined the effects of 12 weeks of CrossFit training on muscular strength, speed, agility, and VO 2max in young male soccer players. Methods: Thirty-eight soccer players were divided randomly into the experimental group (n = 19, age 17.32 ± 1.02 years, body height 1.76 ± 0.15 m, body mass 63.24 ± 5.68 kg, body mass index 21.34 ± 1.32 kg/m 2 ) and control group (n = 19, age 17.21 ± 1.70 years, body height 1.74 ± 0.16 m, body mass 63.43 ± 5.21 kg, body mass index 21.45 ± 1.21 kg/m 2 ). Both groups underwent 12 weeks of the usual soccer training program, including physical exercises on a regular basis, three times a week. Additionally, in the experimental group, a training program based on high-intensity functional physical activity was added during each training session as part of the usual weekly training regimen. Pre-and post-intervention tests were performed to measure player performance, including 30-m sprint, Yo-Yo intermittent recovery test level 1, vertical jump, agility T-test, sit-ups, and push-ups during 60 s. Results: A significant group x time effect was found for all tests: 30-m sprint (p = .012, η p 2 = .42), Yo-Yo test (p = .029, η p 2 = .23), vertical jump (p = .002, η p 2 = .46), T-test (p = .002, η p 2 = .21), sit-ups (p < .001, η p 2 = .55), push-ups (p = .001, η p 2 = .25). The improvement was higher in the experimental group for all variables. Conclusions: CrossFit training is an effective strategy for improving the physical capacities in young soccer players.

back pain is a common complaint among them (Pimentel et al., 2020) . The prevalence of neck and low back pain is higher in SBP than in other postural abnormalities (Lewis & Sahrmann, 2015) . The low back pain in this group of athletes may result from the spinal muscle variations that have occurred due to the SBP. Literature has indicated people with SBP experience forward displacement of the pelvis and backward displacement of the thoracic region (Dol-