Physical exercises proves to be an option to revert a vicious cycle and aggravation of the painful that chronic low back pain can provide, which can improve the mobility and stabilization of the spine, muscle strength, motor coordination and general aerobic conditioning. In addition, photobiomodulation using light emitting diodes (LEDs) has attracted attention for acute and chronic pain and wound healing, being used as a resource for prevention and recovery of lesions. Thus, the present study aims to analyze the efficacy of aerobic training systematized with Deep Water Running associated with photobiomodulation in individuals with chronic nonspecific low back pain. Individuals of both sexes, sedentary, who present chronic low back pain, aged between 30 and 55 years (middle-aged individuals) who meet the inclusion and exclusion criteria will be invited to participate. Anthropometric measurements, maximal stress test, functional tests, physiological measures and questionnaires concerning disability and pain, besides psychological ones, will be carried out. After the evaluations, the participants will be randomized into three experimental groups with 15 participants in each: the first group will be the training group that will hold interval training sessions in addition to continuous training sessions (GT). The second group will perform the same training model, and before the training sessions the LED will be applied (GTL). And the third group will only receive the LED application (GL).

This study will be a randomized clinical trial, structured according to the Consort-Statement, with a standardization that includes methodological design, conduction, analysis and interpretation and evaluation of results. The participants will be individuals of both sexes, sedentary, who present chronic low back pain, aged between 30 and 55 years (middle-aged individuals), will be invited to participate. Participants will be informed of all experimental procedures of the study and will sign the Informed Consent Form and to answer the socio-demographic questionnaire. Participation in the study will be voluntary and free of any bonuses or liens; all participants will be free to withdraw their consent at any time without any loss. Prior to the tests, participants will perform prior clinical examinations with the cardiologist to have their cardiac fitness and release checked to carry out the pertinent evaluations of the study. The possible discomfort felt after the tests and training such as tiredness, muscular pain, perspiration will be similar to the senses during the practice of physical exercises. The procedures to be used in this research will follow the regulations required in Resolution 196/96 of the National Health Council on research involving human beings.

Evaluation protocol Body mass index and skin folds of triceps, subscapular, pectoral, abdominal, thigh mean, suprailiac and mean axillary for subsequent determination of fat percentage.

6-minute walk test-adapted The 6-minute walk test consists of a test that evaluates the distance a person can walk on a flat, rigid surface in six minutes and has as main goal the determination of exercise tolerance and oxygen saturation during a submaximal exercise . This test will be adapted to aquatic environment (CAMARGO et al., 2009).

Sit-up test The sit-up test, which consists of quantifying how many supports (hands and / or knees or, still, hands or forearms on knees), the individual uses to sit and lift from the floor. This method of evaluation allows us to analyze items such as flexibility of the lower limb joints, balance, motor coordination and the relation between muscular power and body weight, which can be characterized as minimum functional muscular fitness (ARAUJO, 1999).

Schober's Test To measure the range of motion of the lumbar spine, the Schober test will be performed, which consists of placing a tape measure from the lumbosacral joint, 10 cm above with the individual in a neutral position, and request the trunk flexion, where the increase of the distance between the marks will provide the estimate of the flexion amplitude of the lumbar spine (Schober, 1937).

Determination of cortisol and creatine kinase's blood markers At the beginning and at the end of the training period, blood samples will be collected for the determination of creatine kinase and cortisol levels. They will be stored in Eppendorf and then centrifuged at 3000rpm for 10 min. Serum will be stored at -20⁰C, while plasma will be discarded, and it wil be read with ck and cortisol analysis kit.

Determination of mood, disability, pain intensity Questionnaires will be applied to monitor the state of beliefs and fears, disability and intensity of pain. The Fear avoidance beliefs questionnaire (FABQ) questionnaire, an instrument for assessing the beliefs and fears of individuals with low back pain and how this pain may affect their physical activities, FABQ-Phys subscale, and occupational subscale, subscale FABQ-Work. It consists of 16 self-report items, which are divided into two subscales: the one that addresses the fears and beliefs of individuals in relation to work and in relation to physical activities. Each item is graded on a seven-point scale, ranging from 0 (completely disagree) to 6 (completely agree) (ABREU et al., 2008), and will be applied at the baseline and after the interventions are completed.

The Oswestry Questionnaire presents 10 sections describing pain or limitations resulting from low back pain, The Oswestry Questionnaire presents 10 sections describing pain or limitations resulting from low back pain, will be applied before and after the intervention period. Each section presents six items, where the zero score indicates little or no pain and / or functional limitation, while score 5 is indicative of extreme pain and / or limitation (VIGATTO, ALEXANDRE and FILHO, 2007).

To evaluate pain intensity, the EVA (COSTA, et al., 2008), which consists of a subjective evaluation of 0 (no pain) to 10 (lots of pain), will be applied in all sessions before and at the end of it. And for a more careful assessment of pain, McGill (PIMENTA and TEIXEIRA, 1996), which is an instrument that provides quantitative information on pain and allows an association with sensorial, affective and evaluative qualities of the process which will be applied at the beginning and at the end of the interventions.

TRAINING PROTOCOL The training sessions will be monitored based on the subjective perception of effort of the session (FOSTER, 1998), and heart rate. There will be two types of training: continuous and hight intensity interval. The sessions of the training group and group training + LED will be preceded by a warm-up of 15 minutes. Participants in the two training groups will undergo weekly training twice weekly in non-consecutive days during the four week period. A total of four continuous training sessions and four high intensity interval training sessions will be held. Continuous training will be 30 minutes at 70 - 80% HRmax, and interval training will be performed 30 minutes high intensity of laced running with fixation of an elastic tube in the floating vest, 30 seconds intense run in maximum effort and 30 seconds of interval.

LED Application The LED application will be performed in the GL and immediately after the GTL training sessions, and will be applied through the spot method with direct contact of the equipment over the irradiated site for 30 seconds. The application will be in the lumbar region, above the gluteal region, with an angle of 90 ° in relation to the cutaneous surface. A wavelength of 660 to 850 nm will be used with a frequency of 0 to 1500 Hz and energy irradiated of 0.9 J of each diode totaling 43.2J (48 diodes).

Inclusion Criteria:

• sedentary
• nonsmoker
• diabetic
• hipertensive
• asthmatic
• cardiovascular disease
• any restriction to the practice of physical exercise
• severe spinal diseases
• previous surgery on the spine
• nerve root compression
• infection or skin lesion at the site of the LED application
• who has been under physiotherapy for chronic low back pain in the last six months

Exclusion Criteria:

• fear of swimming pool
• minimum frequency of 90%
• Unable to finalize training protocol

The participants will be not informed if the LED appliance will be on or off, and the outcomes will be numbers for identification.