Fatigue is an early indicator of negative outcomes in aging, associated with increased risk of disability and mortality. Recently, the term fatigability was coined, which comprises the individual's subjective perception of fatigue in the face of activities of defined duration and intensity. The Pittsburg Fatigability Scale (PFS) is a validated and standardized instrument for the elderly public, which has been translated into Brazilian Portuguese.

To validate the physical subscale of the Brazilian version of the Pittsburgh Fatigability Scale (PFS-Brasil) by evaluating the convergent validity in relation to measures of physical performance.

Validation study of the PFS-Brasil instrument to assess physical fatigability in the Brazilian elderly population. People aged 60 years or over, Brazilians, without neurological, cognitive or orthopedic alterations limiting the performance of the physical test, were invited to participate in the study. The participants performed a measure of physical performance (Short Physical Performance Battery - SPPB) and answered the Brazilian version of the PFS (PFS-Brasil). The evaluations were carried out individually in environments with noise, temperature and lighting control to ensure privacy and comfort conditions for the proper performance of the tests. For the analysis of convergent validity, a search was performed to remove extreme values and Pearson's correlation was calculated between the scores on the physical subscale of the PFS-Brasil and the total score on the SPPB and its subdomains. The Bioestat 5.0 program was used to carry out the statistical analysis.

This study is in progress, and partial data are presented here regarding the evaluation of 57 elderly participants (age: 72.3 ± 6.3 years, 91% women, physically active). The total score on the SPPB was 11.3 (±0.9) points, indicating good functional capacity of the assessed population, consisting of the assessment of gait speed (1.76±0.7 m/s), time to sit and lift 5 repetitions (10.7±2.2 seconds), static balance (3.9±0.4 points). The score in the assessment of physical fatigability by the PFS-Brasil (14.2±9.9 points) demonstrated that there is little perceived physical fatigability in individuals (reference value: < 15 points). The physical fatigability assessment scores demonstrated convergent validity both in relation to the total Short Physical Performance Battery score (r = -0.34, p = 0.0093), and in the gait speed subdomains (r = -0.47, p = 0.0002) and sit-to-stand time 5 repetitions (r = 0.2886, p = 0.0294), but not for static balance (r = -0.2546, p = 0.0559). The correlations indicate that as the value of the total PFS-Brasil score increases (greater perceived fatigability), the total SPPB score, the individual's gait speed and static balance decrease, as does the time to perform the repetitions of sit and stand up from a chair, indicating a low functional capacity.

The PFS-Brasil has convergent validity with a measure of functional capacity in elderly Brazilians.

The characterization of fatigability allows the quantification of an individual's susceptibility to fatigue in the context of standardized physical task(s), being a more sensitive approach to assess the presence and severity of fatigue.