Del Vecchio L; Southern Cross University, Lismore, Australia
Climstein M

Journal of Sports Medicine & Physical Fitness. 66(2):223-231, 2026 Feb

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 R). 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, eta2=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.