Human development and gender inequality are associated with cardiorespiratory fitness: A global systematic review of V̇O_2peak

Background: Cardiorespiratory fitness (CRF) is a powerful predictor of mortality and chronic disease risk, yet global patterns and determinants of CRF remain poorly defined, particularly in females and underrepresented populations. We conducted a systematic review and quantitative synthesis of directly measured peak oxygen uptake (V̇O_2peak) internationally and examined its association with human development and gender inequality. Methods: Studies were eligible if V̇O_2peak was assessed via direct gas analysis during maximal exercise testing, and if the countries had scores for the Human Development Index (HDI) and Gender Inequality Index (GII). Studies were identified through MEDLINE/PubMed, Embase, CINAHL, and Web of Science. Risks of bias were assessed by an adaptation of the Newcastle-Ottawa Scale. Multivariable linear regression models examined associations between V̇O_2peak, age, sex, exercise modality, HDI, GII, and study year. Results: Data included 95 studies from 24 countries with HDI and GII scores, comprising 119,435 adults (42% females) with V̇O_2peak assessed via direct gas analysis during maximal exercise testing. The risk of bias was low. V̇O_2peak was positively associated with HDI (β = 14.1) and negatively associated with GII (β = –3.6). Slightly stronger associations were observed in females than males (HDI: β = 18.9 vs. β = 13.9, GII: β = –4.6 vs. β = –3.6). Young females in middle-HDI countries had higher V̇O_2peak than those in low-HDI countries (31.2 mL/kg/min vs. 28.5 mL/kg/min), with limited additional gains in high-HDI contexts. V̇O_2peak decreased with higher gender inequality, with the largest disparities observed in young females between high- and low-GII countries (26.3 mL/kg/min vs. 32.8 mL/kg/min). Conclusion: Global variation in CRF is tied to national levels of human development and gender equality. These findings support prioritizing structural and policy-level interventions that address social and gender disparities in physical activity access and health promotion. Studies from countries with lower HDI and information on ethnicity and socioeconomic status will bridge crucial gaps in understanding factors involved in global CRF levels.