The relationship between hemoglobin and V˙O2max: A systematic review and meta-analysis

Objective: There is widespread agreement about the key role of hemoglobin for oxygen transport. Both observational and interventional studies have examined the relationship between hemoglobin levels and maximal oxygen uptake (V˙O2max) in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and V˙O2max. Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and V˙O2max (absolute and relative V˙O2max) among both observational and interventional studies. Methods: A systematic search was performed on December 6th, 2021. The study procedures and reporting of findings followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Article selection and data abstraction were performed in duplicate by two independent reviewers. Primary outcomes were hemoglobin levels and V˙O2max values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and V˙O2max values. For interventional studies, meta-analysis models were performed to determine the change in V˙O2max values (standard paired difference) associated with interventions designed to modify hemoglobin levels or V˙O2max. Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in V˙O2max values. Results: Data from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute V˙O2max and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (P