OSAS is characterised by loud snoring, upper airway obstruction, and occasional apnea during sleep. OSAS may affect at least 4% of the men and 2% of the women in middle-age. In Sweden, prevalence figures of 200 000 have been reported. The mechanisms behind OSAS is not fully explained but functionally impaired upper airways muscles, causing a reduction in tonic and phasic contraction during sleep, are proposed one key explanation. The reduced contractions cause partial or complete occlusion of airflow, which in turn cause oxygen desaturation and sleep fragmentation. Patients commonly report everyday life consequences including loud snoring, sleep disturbances, daytime sleepiness, reduced alertness and concentration, and involvement in motor vehicle accidents. Between 7% and 70% of patients suffer from depression and anxiety (figures vary extensively because of methodological differences in existing studies). Due to cardiovascular consequences, OSAS is also linked to hypertension, myocardial infarction, and stroke. Approximately 75% of patients with severe OSAS carry overweight. First line measures recommended for OSAS are conservative including lifestyle modifications, CPAP, and oral appliances. Current state-of-science concludes that CPAP is best possible evidence-based treatment. Despite the use of life style modification recommendations in terms of physical activity and weight loss in accepted guidelines of OSAS, randomised clinical trials supporting these recommendations are rare. Hence, the value of health behaviour modifications has yet to be established. Research within this area is therefore of major interest and urgency, which has motivated the present study design.