Combined and Aquatic Exercise in Chronic Low Back Pain

• Aquatic-exercise Program (Other): This intervention will consist of an aquatic-exercise program, performed in shallow water (120-150 cm deep) at a temperature of 32-34 °C, and supervised by a physiotherapist with over two years of experience in aquatic-based exercise and Ai Chi method. The aquatic-exercise sessions, will consist of a 5-minute warm-up phase, a 30-40-minute training phase, and a 10-15-minute relaxation/cool-down phase, adapted from Ai Chi exercise positions. The Ai Chi method consists of 19 katas (movements) that incorporate deep breathing, coordinated upper and lower limb actions, trunk control, and slow, continuous motion. In this study, only 10 of these 19 katas will be included in the aquatic-exercise protocol.
• Land-based Exercise Program (Other): This program will include specific land-based exercises, supervised by a physiotherapist with more than two years of experience in therapeutic exercise. The land-based exercise program, will be divided into three components: core stability exercises (15-20 minutes), trunk and lower limb stretching exercises (10-15 minutes), and relaxation/coordination exercises adapted from the Ai Chi method (10-15 minutes).
• Home-based Exercise Program (Other): This exercise program will consist of a home-based exercise program. Each session will last 20-30 minutes and will be performed individually at home without professional supervision. The home-based exercise program will include core stability exercises that progress from the supine to the quadruped position. It will mirror the land-based exercise program and is adapted from a previous unsupervised home-based protocol.

Primary outcomes

• Visual Analogue Scale [One measurement will be assessed at baseline and one at each follow-up (8 and 12 weeks).]: Pain intensity will be assessed with the Visual Analogue Scale (Minimum: 0; Maximum 10). Higher values correspond to worse outcome.
• Oswestry Disability Index - version 2.0 [One measurement will be assessed at baseline and one at each follow-up (8 and 12 weeks).]: Disability due to low back pain will be assessed with the Oswestry Disability Index (Minimum: 0; Maximum 100). Higher values correspond to worse outcome.
• Short Physical Performance Battery [One measurement will be assessed at baseline and one at each follow-up (8 and 12 weeks).]: Lower-limb functional capacity (balance, gait speed, chair stands) will be assessed with the Short Physical Performance Battery, a simple tool that includes the four-meter gait speed test, the five-repetition sit-to-stand test and a balance test, and gives a total score based on the performance in each of those tests. Each component is scored (0-4), yielding a composite score (0-12), with higher scores indicating better performance.

Secondary outcomes

• Tampa Scale of Kinesiophobia-13 [One measurement will be assessed at baseline and one at each follow-up (8 and 12 weeks).]: Fear of movement will be assessed with the Tampa Scale of Kinesiophobia-13 (Minimum: 13; Maximum 52). Higher values correspond to worse outcome.
• Hospital Anxiety and Depression Scale [One measurement will be assessed at baseline and one at each follow-up (8 and 12 weeks).]: Anxiety and depression will be assessed with the Hospital Anxiety and Depression Scale (Minimum: 0; Maximum 21). Higher values correspond to worse outcome.
• Fixed Handheld Dynamometry for Assessing Quadriceps Strength [Three measurements will be assessed at baseline and three at each follow-up (8 and 12 weeks).]: Quadriceps muscle (both sides) maximum voluntary isometric contraction will be assessed with Fixed Handheld Dynamometry with participants seated and the knee positioned at approximately 90° of flexion.
• Hand-Grip Dynamometry [Three measurements will be assessed at baseline and three at each follow-up (8 and 12 weeks).]: Maximum isometric strength of the hand and forearm muscles (both sides) will be assessed with Hand-Grip Dynamometry with participants seated with the elbow flexed at 90° and the forearm in a neutral position.
• Modified-Modified Schober Test [Three measurements will be assessed at baseline and three at each follow-up (8 and 12 weeks).]: Lumbar spine range of motion will be assessed with the Modified-Modified Schober Test.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* all genders;
* aged over 18 years;
* Chronic Low Back Pain lasting three months or longer and with an intensity of 3 or higher on the Visual Analogue Scale at rest.

Exclusion Criteria:

* Individuals who refuse to participate or do not provide informed consent;
* Pain radiating to the lower limb;
* Recent pregnancy or childbirth (less than 8 weeks ago);
* Ongoing physical therapy treatments;
* Severe rheumatological, neurological, neoplastic, cardiovascular diseases or other conditions that could prevent full participation in the intervention;
* History of spinal surgery;
* Inflammatory, infectious, or malignant spinal diseases;
* Psychiatric disorders that may affect adherence and symptom assessment.

• Pedro Duarte-Mendes, PhD, Study director, Instituto Politécnico de Castelo Branco
• Henrique Neiva, PhD, Study director, University of Beira Interior
• Diogo Monteiro, PhD, Study director, Instituto Politécnico de Leiria