Fatigue is a symptom associated with the weakening or depletion of an individual's physical and/or mental resources. The term fatigability comprises the subjective perception of fatigue in face of activities of specific intensity and duration. The Pittsburg Fatigability Scale (PFS), originally published in English, is the only validated scale to measure perceived fatigability in older adults. Considering the importance of specific assessment in the aging population for the prevention of conditions and for the rehabilitation, it is necessary to translate and adapt it cross-culturally to the specificities of the Brazilian context.

To translate and cross-culturally adapt the Pittsburgh Fatigability Scale into Brazilian Portuguese to assess fatigability in the Brazilian older adult's population.

Based on Beaton et al. (2000) we carried out the translation and cross-cultural adaptation to generate the PFS version in Brazilian Portuguese (PFS-Brasil), following the steps: translation from the source language (English), comparison and synthesis of translated versions, blind back-translation, comparison of back-translations and assessment of instrument clarity by the expert committee. Older adults who met the inclusion and exclusion criteria were invited to participate voluntarily. Each participant provided demographic data, responded to the PFS-Brasil and reported their understanding, difficulty in responding and suggestions about each item on the scale. All assessments were performed in environments with noise, temperature, and lighting control to ensure privacy and comfort conditions for the proper performance of the tests. The R software was used to analyze the evidence of construct validity and instrument precision based on Confirmatory Factor Analysis (CFA), Cronbach's α, McDonald's ω and composite reliability.

The Brazilian version of the PFS (PFS-Brasil) was developed. The pilot test referring to the last phase of the cross-cultural adaptation included the assessment of 103 participants. Confirmatory factor analyzes carried out point to the adequacy of bifactorial models for both subscales, with satisfactory and excellent internal consistency for the physical and mental subscales, respectively.

The present study demonstrated that the Brazilian version of the Pittsburgh Fatigability Scale has adequate construct validity for assessing perceived fatigability in older adults, both in its physical and mental subscales.

To have an assessment tool that is easy to use, brief, easy to understand and validated for our culture is essential for proper clinical assessment. The PFS-Brasil scale analyzes the degree of perceived physical and mental fatigability in the older adult and the scale will allow health professionals to assess health conditions in a comprehensive and precise way, defining rehabilitation procedures and its follow-up for the integral health care of the aging populations. To analyses other validation parameters are needed and are being performed as part of a second study.