Evaluation of the convergent validity of an estimated cardiorespiratory fitness algorithm

Examine the convergent validity of a cardiorespiratory fitness (CRF) algorithm when compared to treadmill-assessed CRF. Data from the 1999-2004 NHANES were used (N = 3259 adults 20-49 years). Cardiorespiratory fitness was estimated from an algorithm. Participants completed a submaximal treadmill-based protocol. We (1) evaluated the pairwise association (and ICC) between estimated and measured cardiorespiratory fitness, (2) employed a paired samples t test to examine potential mean differences between estimated and measured cardiorespiratory fitness, (3) constructed a Bland-Altman plot and 95% limits of agreement (LoA) to explore systematic differences and random error between estimated and measured cardiorespiratory fitness, and (4) examined the association (via linear regression) of estimated and measured cardiorespiratory fitness with chronic disease prevalence and C-reactive protein (CRP). Mean estimated CRF (10.68 METs) was lower than the mean measured CRF of 11.37 METs (p < 0.0001). The calculated pairwise correlation was of a moderate strength, r = 0.43 (p < 0.0001), with an ICC of 0.40 (p < 0.001). Calculated LoA indicated that estimated CRF may differ from measured CRF by 40% below to 48% above. Regression analyses yielded statistically significant inverse associations of estimated (unstandardized coefficient = - 0.026; p < 0.001) and measured (unstandardized coefficient = - 0.007; p = 0.002) CRF with chronic disease and estimated (unstandardized coefficient = - 0.08; p < 0.001) and measured (unstandardized coefficient = - 0.03; p < 0.001) CRF with CRP. Measured and estimated CRF were moderately correlated. However, estimated and measured CRF were statistically significant different from one another with noteworthy scatter around the average difference. As such, when feasible, objective measurements of CRF should be taken.