Background. Primary hypothyroidism, both clinical and subclinical, is frequently associated with persistent fatigue, reduced psychological well-being, and lower levels of physical activity in adult women. However, evidence integrating these psychosocial factors remains limited and methodologically heterogeneous.

Objective. To analyze the association between physical activity and fatigue, social support, and psychological well-being in women with primary hypothyroidism; to compare these profiles between clinical and subclinical hypothyroidism; and to explore the moderating effect of social support and psychological well-being on the relationship between fatigue and physical activity.

Methods. An observational, analytical, multicenter cohort study will be conducted including 96 adult women with primary hypothyroidism from the Principality of Asturias. Physical activity levels will be assessed using the International Physical Activity Questionnaire-Short Form (IPAQ-SF), while fatigue, social support, and psychological well-being will be measured using the Fatigue Severity Scale (FSS), the Medical Outcomes Study Social Support Survey (MOS-SSS), and the WHO-5 Well-Being Index, respectively. Confounding variables will include age, body mass index, type of hypothyroidism (clinical or subclinical), and time since diagnosis. Descriptive analyses, comparisons between clinical and subclinical groups, and multiple linear regression models will be performed.

Expected results. The study is expected to identify physical activity levels within the sample and determine which psychosocial factors are independently associated with physical activity. Additionally, fatigue is anticipated to be negatively associated with physical activity, whereas social support and psychological well-being are expected to show positive associations and potential moderating effects.

Inclusion Criteria:

• Have a diagnosis of primary hypothyroidism (clinical or subclinical), established by a specialist in Endocrinology or Internal Medicine based on TSH and FT4 levels.
• Female.
• Are aged ≥18 years at the time of inclusion.
• Have stable treatment for thyroid dysfunction (levothyroxine dose or other replacement regimen without relevant modifications) for at least the previous 3 months, or a stable clinical condition if treatment is not required.
• Are able to ambulate independently in the community (with or without usual assistive devices), allowing participation in light to moderate physical activity.
• Are able to understand and complete the questionnaires independently.
• Have provided written informed consent

Exclusion Criteria:

• Have a diagnosis of severe medical conditions that predominantly limit the ability to perform physical activity independently of hypothyroidism (e.g., advanced heart failure, severe chronic respiratory disease).
• Have severe psychiatric disorders or significant cognitive impairment that hinder understanding of the information or reliable completion of the questionnaires.
• Have undergone major surgery, severe trauma, or an acute medical condition that has substantially limited physical activity in the three months prior to assessment.
• Are pregnant or in the immediate postpartum period, due to potential hormonal and functional interference with the study variables.
• Are concurrently participating in a clinical trial or a structured physical exercise program.

Women with primary hypothyroidism