Purpose: This study aimed to cross-validate a recently proposed equation for the prediction of maximal oxygen uptake (${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$) in cycling exercise by using the average power output normalized by the body mass from a 5-minute time trial (RPO_5-min) as the independent variable. Further, the study aimed to update the predictive equation using Bayesian informative prior distributions and meta-analysis. Methods: On different days, 49 male cyclists performed an incremental graded exercise test until exhaustion and a 5-minute time trial on a stationary cycle ergometer. We compared the actual ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ with the predicted value obtained from the RPO_5-min, using a modified Bayesian Bland–Altman agreement analysis. In addition, this study updated the data on the linear regression between ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ and RPO_5-min, by incorporating information from a previous study as a Bayesian informative prior distribution or via meta-analysis. Results: On average, the predicted ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ using RPO_5-min underestimated the actual ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ by −6.6 mL·kg^–1·min^–1 (95% credible interval, −8.6 to −4.7 mL·kg^–1·min^–1). The lower and upper 95% limits of agreement were −17.2 (−22.7 to −12.3) and 3.8 (−1.0 to 9.5) mL·kg^–1·min^–1, respectively. When the current study’s data were analyzed using the previously published data as a Bayesian informative prior distribution, the accuracy of predicting sample means was found to be better when compared with the data combined via meta-analyses. Conclusions: The proposed equation presented systematic bias in our sample, in which the prediction underestimated the actual ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$. We provide an updated equation using the previous one as the prior distribution, which could be generalized to a greater audience of cyclists.