Determining an Indicator of Physical Fitness Age for Middle-Aged and Older Adults Based on a Nationwide Population-Based Study in China

To better determine the rate of aging and offer tailored intervention or medical care, it is essential to create a comprehensive indicator that can evaluate physical fitness in middle-aged and older people. This study aimed to create an indicator of physical fitness age (PFA) that can be used to comprehensively evaluate physical performance and to confirm its validity. There were 5,368 participants in the constructing PFA group and 1,846 participants in the validating PFA group (aged ≥40 for all). We measure five physical fitness items to develop PFA by using principal component analysis. To assess the validity of PFA, we compared chronological age (CA) and PFA in participants with and without possible sarcopenia and used receiver operating characteristic (ROC) curve analysis to assess the discriminating power of the CA and PFA in identifying possible sarcopenia. We established an indicator of PFA which was expressed as PFA = 24.857 − 0.034 × peak expiratory flow − 0.609 × handgrip strength + 9.238 × walking speed + 1.238 × 5-time chair stand test + 0.742 × CA for men, and PFA = 22.171 − 0.051 × peak expiratory flow − 0.735 × handgrip strength + 7.603 × walking speed + 1.108 × 5-time chair stand test + 0.753 × CA for women. The validation test demonstrated that PFA was statistically lower than CA in participants without possible sarcopenia, while the PFA was significantly greater than CA in those with possible sarcopenia. ROC analysis showed that PFA had a larger area under the curve than CA. The findings suggest that PFA is a valid predictor of physical performance in Chinese middle-aged and older adults, which can discriminate persons of the same CA but different levels of physical performance.