We determined the effects of augmented inspiratory and expiratory intrathoracic (P_ITP) or abdominal (P_ABD) pressure excursions on within-breath changes in femoral venous blood flow (Q_fv) and net Q_fv in the steady state during tightly controlled (total breath time = 4 seconds; inspiratory time/total breath time = 0.5) accessory muscle/"ribcage" (P_ABD < 2 cm H₂O) or diaphragmatic (P_ABD > 5 cm H₂O) breathing patterns. Selectively augmenting the inspiratory P_ITP excursion during ribcage breathing augmented the inspiratory facilitation of Q_fv from the resting limb (69% of all flow occurred during inspiration during non-loaded conditions, 89% during inspiratory loaded conditions), though net Q_fv in the steady-state was not altered due to slight reductions in femoral venous return during the ensuing expiratory phase of the breath. Selectively augmenting the inspiratory P_ES excursion during a predominantly diaphragmatic breath at rest did not alter the within-breath changes in Q_fv relative to non-loaded conditions (net retrograde flow of -9 ± 12% during non-loaded conditions, -4 ± 9% during inspiratory loaded), supporting the notion that the inferior vena cava is completely collapsed by relatively small increases in P_GA. However, the addition of combined inspiratory and expiratory loading to diaphragmatic breathing at rest resulted in a reversal of the within-breath changes in Q_fv, such that >90% of all anterograde Q_fv now occurred during inspiration. Combined inspiratory and expiratory loading also reduced steady-state Q_fv during calf contractions of both mild and moderate intensities when compared to inspiratory loading alone. From these data, we conclude that: 1) exaggerated inspiratory pressure excursions may augment within-breath changes in femoral venous return but do not increase net femoral venous blood flow in the steady state, and 2) active expiration during diaphragmatic breathing reduces the steady-state hyperemic response to dynamic exercise by mechanically impeding venous return from the locomotor limb, which may ultimately contribute to exercise limitation in both health and disease.