Risk of bias among interventional articles.

ObjectiveThere 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 () in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and . Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and (absolute and relative ) among both observational and interventional studies.MethodsA 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 values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and values. For interventional studies, meta-analysis models were performed to determine the change in values (standard paired difference) associated with interventions designed to modify hemoglobin levels or . Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in values.ResultsData from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (PPP = 0.006)).ConclusionThese findings suggest that values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.</div

PRISMA flow diagram.

Flow diagram displaying the selection of articles through different phases of the systematic review, and categorization of included articles.</p

Risk of bias among observational articles.

ObjectiveThere 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 () in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and . Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and (absolute and relative ) among both observational and interventional studies.MethodsA 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 values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and values. For interventional studies, meta-analysis models were performed to determine the change in values (standard paired difference) associated with interventions designed to modify hemoglobin levels or . Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in values.ResultsData from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (PPP = 0.006)).ConclusionThese findings suggest that values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.</div

The association between erythropoiesis stimulating agents and change in maximal oxygen uptake (absolute ).

Forest plot depicting the effect size of the change in absolute (standard paired difference) following administration of erythropoiesis stimulating agents. Different size symbols indicate relative weights used in meta-analyses and are proportional to study size. Abbreviations: SD, standard error.</p

PRISMA 2020 checklist.

ObjectiveThere 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 () in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and . Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and (absolute and relative ) among both observational and interventional studies.MethodsA 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 values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and values. For interventional studies, meta-analysis models were performed to determine the change in values (standard paired difference) associated with interventions designed to modify hemoglobin levels or . Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in values.ResultsData from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (PPP = 0.006)).ConclusionThese findings suggest that values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.</div

Hemoglobin levels as covariates of absolute and relative maximal oxygen uptake () derived from observational analyses.

Hemoglobin levels as covariates of absolute and relative maximal oxygen uptake () derived from observational analyses.</p

Association between hematocrit and maximal oxygen uptake ().

Bubble plot and meta-regression displaying the positive association between hematocrit and both absolute (A) and relative (B). Data for males are represented as purple bubbles, data for females are represented as green bubbles with plus sign symbols, and data for studies presenting males and females pooled (mixed) are represented as black bubbles with middle dot symbols. Each bubble represents a group from a single study and the size of bubbles represents the number of participants within each group. The solid line indicates the meta-regression line, and the dashed lines indicate the 95% prediction interval associated with the meta-regression. (DOCX)</p

Association between hemoglobin concentration and maximal oxygen uptake ().

Bubble plot and meta-regression displaying the positive association between hemoglobin concentration and both absolute (A) and relative (B). Data for males are represented as purple bubbles, data for females are represented as green bubbles with plus sign symbols, and data for studies presenting males and females pooled (mixed) are represented as black bubbles with middle dot symbols. Each bubble represents a group from a single study and the size of bubbles represents the number of participants within the group. The solid line indicates the meta-regression line, and the dashed lines indicate the 95% prediction interval associated with the meta-regression. (DOCX)</p

The association between blood donation or transfusion and change in maximal oxygen uptake (absolute ).

Forest plots depicting the effect size of the change of absolute (standard paired difference) following blood transfusion or donation. Different size symbols indicate relative weights used in meta-analyses and are proportional to study size. Abbreviations: SE, standard error.</p

The association between change in hemoglobin concentration and change in absolute maximal oxygen uptake () following blood donation or transfusion.

Meta-regression and bubble plot depicting the relationship between the change in hemoglobin concentration and the effect size of the change in absolute (standard paired difference) among independent subgroups following blood transfusion or donation. Different size symbols indicate relative weights used in the meta-regression and are proportional to study sample size.</p