Fig 4. The association between change in hemoglobin concentration and change in absolute maximal oxygen uptake ($\dot{\mathbf{V}}{\mathbf{O}}_{\mathbf{2}}\mathbf{m}\mathbf{a}\mathbf{x}$) 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 $\dot{\mathrm{V}}{\mathrm{O}}_2\mathrm{m}\mathrm{a}\mathrm{x}$ (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.