Table 1. Hemoglobin levels as covariates of absolute and relative maximal oxygen uptake ($\dot{\mathbf{V}}{\mathbf{O}}_{\mathbf{2}}\mathbf{m}\mathbf{a}\mathbf{x}$) derived from observational analyses.

	Absolute $\dot{\mathbf{V}}{\mathbf{O}}_{\mathbf{2}}\mathbf{m}\mathbf{a}\mathbf{x}$ (L·min-1)
	Coefficient [95% CI]	P value	R 2	τ 2	n
Hemoglobin mass
All data	0.005 [0.003, 0.007]	<0.0001	0.49	0.34	42
Males	0.006 [0.004, 0.009]	<0.0001	0.66	0.41	23
Females	0.011 [0.008, 0.015]	<0.0001	0.92	0.31	8
Hemoglobin concentration
All data	0.404 [0.298, 0.510]	<0.0001	0.29	0.77	199
Males	0.148 [0.022, 0.274]	0.022	0.15	0.51	141
Females	0.226 [0.060, 0.393]	0.008	0.22	0.31	41
	Relative $\dot{\mathbf{V}}{\mathbf{O}}_{\mathbf{2}}\mathbf{m}\mathbf{a}\mathbf{x}$ (mL·min -1 ·kg -1 )
Hemoglobin mass
All data	0.058 [0.039, 0.077]	<0.0001	0.55	130.27	58
Males	0.054 [0.024, 0.084]	<0.0001	0.19	67.75	37
Females	0.137 [0.016, 0.258]	0.027	0.34	28.44	8
Hemoglobin concentration
All data	4.649 [2.650, 6.648]	<0.0001	0.10	121.87	284
Males	0.882 [-1.120, 2.884]	0.388	0.02	83.77	175
Females	5.999 [3.249, 8.728]	<0.0001	0.45	67.59	63

Data depict results of independent meta-regressions in determination of hemoglobin levels (hemoglobin mass and hemoglobin concentration) as covariates of absolute $\dot{\mathrm{V}}{\mathrm{O}}_2\mathrm{m}\mathrm{a}\mathrm{x}$ and relative $\dot{\mathrm{V}}{\mathrm{O}}_2\mathrm{m}\mathrm{a}\mathrm{x}$. Data were pooled from each study to provide one single data point for ‘All data’ derived coefficients (n denotes the number of studies). Additional independent analyses were performed for subgroups of data reporting males only and females (n denotes the number of subgroups). Abbreviations: CI, confidence interval.