Exploring oxygen uptake efficiency slope as an accessible marker of aerobic fitness in middle-aged adults

OUES can be reliably obtained using a brief treadmill protocol and portable metabolic equipment in middle-aged adults. While not associated with self-reported activity, OUES showed moderate correlations with VO<inf>2</inf>max and differentiated higher-fitness individuals, especially by sex. These findings support OUES as a valid submaximal marker of cardiorespiratory fitness and underscore the importance of objective fitness measures alongside self-report tools in health and exercise settings.