Background: Chronic low back pain (LBP) can lead to major functional disabilities and force people to take time off work, sports or leisure activities. Regular physical exercise is an important ally in reducing the risk factors for most diseases, and CrossFit® is one of the modalities that has been gaining momentum when choosing an exercise. However, the intensity recommended in training can collaborate with the development of musculoskeletal problems such as pain and postural changes, interfering with the development of the practice, with low back pain being one of the most common disorders in these practitioners, especially caused by mechanical stress. Considering that CrossFit® practitioners have already incorporated physical exercise into their routine, passive techniques such as myofascial release (ML) have been discussed as a form of treatment for LBP. For this reason, this study was designed to verify the efficacy of ML in the LBP of CrossFit® practitioners, comprising two techniques, one manual and one instrumental, and to see if the outcome of the LBP alters the posture of the spine. This is a randomised controlled clinical that will be conducted in a CrossFit® box in the city of Goiânia-GO, Brazil. At least 51 people will take part who have been doing CrossFit® for at least 3 months, who have LBP, are aged between 18-59 and are not undergoing any other treatment for low back pain. There will be two experimental groups, one that will receive manual MR and the other, cupping therapy, as well as a control group that will not receive any technique. The sessions will take place twice a week for 8 weeks. The primary outcome will be low back pain intensity, assessed at baseline, weekly and after 8 weeks, and the secondary outcomes, which will be postural deviations, spinal mobility and history of musculoskeletal pain, assessed at baseline and at the end of 8 weeks. There will be no blinding between therapist and participants. Discussion: This study will investigate whether MR is effective in relation to LBP, given that some results have already shown positive responses in acute conditions, while also verifying the repercussions on the postural aspect. The results could provide additional knowledge about the best technique to use and, having applicability to our outcomes, will favour and simplify treatment, helping professionals to make clinical decisions.