Background

Cardiorespiratory fitness, typically measured as peak oxygen uptake (V̇o2peak) during maximal graded exercise testing (GXTmax), is a predictor of morbidity, mortality, and cardiovascular disease. However, measuring V̇o2peak 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 V̇o2peak 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 V̇o2peak (mL·kg−1·min−1), and HRRec measures after a GXTmax in 61 young (25.2 ± 6.1 years), sedentary adults (40 females) using 3 methods. We examined the relationship between V̇o2peak and absolute (b.min−1) and relative (%) HRRec measures at 1, 2, and 3 min post GXTmax, as well as a measure of the slow component HRRec (HRRec 1 min minus HRR 2 min), using Pearson's correlation analysis.

Results

V̇o2peak (36.5 ± 7.9 mL·kg−1·min−1) was not significantly correlated with absolute HRRec at 1 min (r = 0.18), 2 mins (r = 0.04), or 3 min (r = 0.01). We also found no significant correlations between V̇o2peak and relative HRRec at 1 min (r = 0.09), 2 min (r = −0.06), or 3 min (r = −0.10). Lastly, we found no correlation between the measure of the slow component HRRec and V̇o2peak (r = −0.14).

Conclusion

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

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