What is real change in submaximal cardiorespiratory fitness in older adults? Retrospective analysis of a clinical trial

OBJECTIVE: To assess the test–retest reliability of submaximal cardiorespiratory fitness in healthy active older adults. METHODS: This was a retrospective analysis of 41 adults enrolled in a clinical trial [mean (sd) aged 59 yrs (7); 29% females; and body mass index 24.5 kg/m(2) (3.3)]. Cardiorespiratory fitness was assessed using a cycle ergometer 6 weeks apart. The initial workload was 1 W per kilogram of free fat mass (W/kg FFM) and increased by 0.5 W/kg FFM every 3 min until participants could not maintain the speed at ≥ 60 rpm, they reached a rating of perceived exertion of 15–17, and/or obtained a respiratory exchange ratio (RER) of 1.000. Reliability of [Formula: see text] (,) heart rate and RER was assessed for each workload, and for [Formula: see text] (,) when RER reached 1.00. Reliability was examined as the intraclass correlation coefficient (ICC((2,1))), Bland–Altman plots, standard error of measurement (SEM and SEM%), and the minimal detectable change (MDC). RESULTS: Test–retest agreement ranged between (ICC((2,1)) 0.44–0.84) with no discernible systematic differences between assessments. The SEM% for absolute and relative [Formula: see text] ranged between 13.0 to 20.2%, and 13.8 to 26.3%, respectively(.) The MDC(90)% for absolute and relative [Formula: see text] ranged between 30.4% to 47.1%, and 32.2% to 61.4%, respectively. The lowest SEMs% and MDCs% for both absolute and relative [Formula: see text] were observed for workloads at 2.5 W kg/FFM (~ 13% and ~ 31%, respectively). CONCLUSIONS: Although at least modest relative reliability was consistently demonstrated, the smaller measurement error associated with absolute and relative [Formula: see text] at 2.5 W kg/FFM may indirectly suggest that submaximal cardiorespiratory fitness can be monitored more confidently at higher workloads. Findings provide critical information to determine how much change is considered ‘real change’ in repeated measures of cardiorespiratory fitness using a submaximal graded exercise testing protocol in healthy active older adults. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40798-022-00447-6.