Recent studies and meta-analysis showed that different exercise plans had greater benefits than no invention group in improving pain, physical function, and disease activity, especially in some studies that involve ankylosing spondylitis patients receiving home-based exercise. Different kinds of exercises are efficacious and should be recommended to AS patients. But, according to our current knowledge, no clear protocols regarding the effectiveness of hippotherapy in AS patients.

This study aims to investigate the effect of the therapeutic horseback riding therapy via a mechanical simulator on disease-specific outcomes and muscle strength of ankylosing spondylitis patients.

Hippotherapy or therapeutic horseback riding therapy is a form of animal-assisted therapy that uses the horse as a modality that aims to improve postural control, balance, and mobility. With hippotherapy, it is aimed to change the center of gravity by using the movements of the horse and to ensure the adaptation of the trunk and pelvis by developing righting and balance reactions against this new position. Current studies suggest that hippotherapy may be a useful complementary treatment approach for improving balance, fatigue, spasticity, walking, and quality of life in different kinds of disabilities. However, horseback riding therapy itself has some limitations as a treatment due to costs, location, and risks. By its nature horse-riding is too dynamic for patients and requires a large outdoor space. It is believed that a hippotherapy simulator is a therapeutic exercise option for the treatment of thoracolumbar segmental instability and hypo-mobility. Besides complications such as fractures caused by falling are greatly reduced using hippotherapy simulators under proper supervision. Hippotherapy with a mechanical stimulator simulates the motion of a horse as part of a continuous therapy package to provide postural or stability training. This exercise develops unified intuitive stimulation plus motor responses. It engages movement hits that are produced by the machine which mimicking the animal walks: this leads to beneficial consequences.

This prospective clinical study aims to investigate the effect of therapeutic horseback riding therapy via a mechanical simulator on disease-specific outcomes and muscle strength of ankylosing spondylitis patients.

This randomized, single-blind, controlled clinical trial will carry out at the University of Usak/ TURKEY.

This randomized, single-blind, controlled clinical trial will carry out at the University of Usak/ TURKEY. The study will include a total of 60 volunteers who had been diagnosed with AS according to the modified New York criteria. The subjects will be patients who are referred to the outpatient physical therapy center of the Physical Medicine and Rehabilitation Department of the Usak University.

Participants will be allocated to the different treatment groups using the block randomization method. All patients in both groups will continue their ongoing medications. But also, both groups will plan to complete exercise sessions 3 times a week for 12 weeks, each lasting 35 minutes per day.

For Group 1 (horse-riding simulator group), patients will perform a horse riding simulation exercise at speeds of 15km/h, 18km/h, 20km/h, 22km/h, 25km/h, each lasting 5 minutes after warm-up for 5 minutes in each session. Then they will rest for five minutes. For safety, a physiotherapist will be accompanied to the exercises for this group.

For Group 2 (home exercise group) patients will perform home exercises. Home exercises will be consist of a warm-up, stretching, balance, back walking, fingertip walking exercises, the first of which is shown by the physiatrist or physiotherapist to the patients. These patients will be called twice a month to ask whether they have done the exercises, and the patients whose participation rate is below 80% will be excluded from the study by following the exercise schedule when they come to the physician's control monthly.

During the study, if, any subject making any changes to the drug treatment will withdraw from the study.

Evaluations will make before and after treatment. All evaluations will perform by the same experienced physiotherapists who will be blind to the study groups.

Primer outcomes of the study; The Bath AS Disease Activity Index (BASDAI) and Bath AS Disease Functional Index (BASFI) will be used for the activity-related disease, function, and baseline measurements of the participants, respectively.

Quadriceps muscle strength will be measured with the microFET®2 Dynamometer. Bath AS Disease Activity Index (BASDAI): This index, which was developed to evaluate disease activity, consists of 6 VAS measurements. These are fatigue, spine, and peripheral joint pain, sensitivity, and morning stiffness measurements.

Bath AS Disease Functional Index (BASFI): BASFI measures the functional capacity of the patient in the previous week. This index consists of 8 questions about daily activities and 2 questions evaluating the patient's ability to cope with daily life. The degree of difficulty felt by the patient in performing specified tasks is marked on a 10 cm visual analog scale. The average of the total score obtained from 10 questions is calculated for use in the analysis.

Quadriceps muscle strength will be measured with the microFET2 Dynamometer. The wireless microFET®2 Digital Handheld Dynamometer muscle tester is an accurate, portable Force Evaluation and Testing device. It is a modern adaptation of the time-tested art of hands-on manual muscle testing. Measurement Range 0-300 lbs force.

Inclusion Criteria:

• Ankylosing spondylitis diagnosis according to the modified New York criteria
• Voluntary participation in the study
• Age 18-45 years
• Regular use of disease-modifying anti-rheumatic drugs (methotrexate, sulfasalazine, and anti-tumor necrosis factor (TNF) agents) at a stable dosage for at least six weeks.

Exclusion Criteria:

• Exercising regularly during the previous six months.
• The presence of severe comorbidity that may affect the kidneys, liver, lungs, and heart such as cardiovascular, pulmonary, orthopedic, and neurological problems.
• Problems that may prevent exercise (uncontrollable hypertension, heart attack or history of coronary revascularization, history of syncope or exercise-related arrhythmia, decompensated Type 1 diabetes mellitus, history of hip and/or knee arthroplasty)
• Having undergone any surgery in the previous 6 months
• Any other neuromuscular disease that may affect the muscles' strength.
• Inability to participate in at least 80% of the exercises

All evaluations for outcomes will perform by the same experienced physiotherapists who will be blind to the study groups.