Therefore, investigators will undertake a rigorous assessment of a practical UA muscle training on OSA. Investigators will recruit patients with OSA that are wither unable/unwilling to use CPAP, as well as those who are already on treatment with PAP or oral appliances. The exercises include 4 steps: step 1 is to put on an individualized fitted oral retainer device to guide the exercise; step 2 is to push the tongue towards the hard palate to press the movable part of the oral retainer device for 4 minutes; step 3 is to touch the hard palate using the middle part of the tongue, hold for 10 seconds and repeat it for 4 minutes; step 4 is to remove the retainer device and brush the tongue gently on both sides for 2 minute. The exercise will take 20 minutes a day (10 minutes in the morning and 10 minutes in the afternoon/evening).