Heart rate recovery as an assessment of cardiorespiratory fitness in young adults.

Background: Cardiorespiratory fitness, typically measured as peak oxygen uptake (VO) during maximal graded exercise testing (GXT), is a predictor of morbidity, mortality, and cardiovascular disease. However, measuring VO is costly and inconvenient and thus not widely used in clinical settings. Alternatively, postexercise heart rate recovery (HRRec), which is an index of vagal reactivation, is a valuable assessment of VO in older adults and athletes. However, the validity of HRRec as a clinical indicator of cardiorespiratory fitness in young, sedentary adults, who are a rapidly growing population at risk for developing obesity and cardiovascular disease, has not been fully elucidated.

Methods: We investigated the association between cardiorespiratory fitness, measured by VO (mL·kg·min), and HRRec measures after a GXT in 61 young (25.2 ± 6.1 years), sedentary adults (40 females) using 3 methods. We examined the relationship between VO and absolute (b·min) and relative (%) HRRec measures at 1, 2, and 3 min post GXT, as well as a measure of the slow component HRRec (HRRec 1 min minus HRR 2 min), using Pearson's correlation analysis.

Results: VO (36.5 ± 7.9 mL·kg·min) was not significantly correlated with absolute HRRec at 1 min ( = 0.18), 2 min ( = 0.04) or 3 min ( = 0.01). We also found no significant correlations between VO and relative HRRec at 1 min ( = 0.09), 2 min ( = -0.06) or 3 min ( = -0.10). Lastly, we found no correlation between the measure of the slow component HRRec and VO ( = -0.14).

Conclusions: Our results indicate that HRRec measures are not a valid indicator of cardiorespiratory fitness in young, sedentary adults.