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Exploring oxygen uptake efficiency slope (OUES) as an accessible marker of aerobic fitness in middle-aged adults
Journal article   Peer reviewed

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

Luke Del Vecchio and Mike Climstein
The Journal of Sports Medicine and Physical Fitness, Vol.66(2), pp.223-231
02/2026
DOI: https://doi.org/10.23736/S0022-4707.25.17226-5
Appears in  Recent Faculty of Health Publications

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Abstract

Oxygen consumption Middle aged Exercise
BACKGROUND: The oxygen uptake efficiency slope (OUES) is a submaximal, effort-independent index derived from cardiopulmonary exercise testing that reflects aerobic fitness. Although OUES has shown strong correlations with maximal oxygen uptake (VO2max) in clinical populations, its validity and relationship with habitual physical activity in healthy middle-aged adults remain underexplored. This study aimed to evaluate OUES as a marker of aerobic fitness and examine its association with self-reported physical activity in this demographic. METHODS: Twenty-one middle-aged adults (14 women, seven men; mean age 63.3±3.8 years) without known cardiopulmonary disease were recruited. Participants completed the Sports Medicine Australia pre-exercise screening questionnaire, including weekly physical activity reporting. Each participant underwent a graded treadmill test (Bruce protocol) to submaximal effort, with oxygen uptake (VO2) and ventilation (VE) measured continuously using a validated portable metabolic system. OUES was calculated from the linear regression of VO2 against the log10VE). VO2max was estimated via a resting seismocardiography device (VentriJect Seismofit®). Pearson’s correlations and one-way ANOVA were used to evaluate relationships between variables and tertile-based fitness groups. An independent-samples t-test compared OUES values by sex. RESULTS: Mean peak VO2 was 25.2±4.1 mL/kg/min; mean OUES was 1629.6±522.0 mL/min per log L/min. OUES showed a moderate but non-significant correlation with estimated VO2max (r=0.415, P=0.069) and no meaningful association with self-reported physical activity (r=-0.012, P=0.960). One-way ANOVA showed significant differences in VO2max across VentriJect VO2 tertiles (P<0.001, η2=0.65), but not in OUES (P=0.162). Males had significantly higher OUES values than females (2171±391 vs. 1366±282; P<0.001), with a large effect size (Cohen’s d=2.50). CONCLUSIONS: 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 VO2max 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.

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