Purpose: To examine muscle oxygenation during running with and without blood flow restriction (BFR). Methods: Fifteen aerobically trained males randomly completed four, three-minute running bouts at 70%BFR, 80%BFR, and 90%BFR of their top speed with BFR and 100%NOBFR of their top speed without BFR. Oxygenated hemoglobin (O2Hb), deoxygenated Hb (HHb), total Hb (tHb), Hb difference (HbDiff) and muscle tissue oxygenation (StO2) were assessed continuously throughout the running bouts. Separate two-way, 4 (Intensity [70%BFR, 80%BFR, 90%BFR, 100%NOBFR])33 (Time [120, 150, and 180 s]), repeatedmeasure ANOVA models were constructed to examine O2Hb, HHb, tHb, HbDiff, and StO2 responses. Results: O2Hb decreased (120- [65.25 +- 6.58%] > 150-s [63.72 +- 6.75%]), while HHb increased (120- [14.4 +- 12.55%] < 150- [16.91 +- 12.6%] < 180-s [18.26 +- 12.87%]) (P < 0.001). tHb was similar across time (P - 0.159) and between intensities (P - 0.454). HbDiff decreased (120- [73.56 +- 6.54%] > 150[71.66 +- 6.61%] > 180-s [70.98 +- 6.93%]). StO2 decreased and then plateaued (120- > 150- and 180-s) during the 70%BFR (51.87 +- 5.09% > 51.20 +- 5.37% and 51.02 +- 5.21%) (P - 0.004), 80%BFR (52.2 +- 3.93% > 51.34 +- 4.17% and 51.01 +- 4.09%) (P - 0.008), and 100%NOBFR (51.69 +- 4.6% > 50.84 +- 4.87% and 50.62 +- 4.89%) (P < 0.001) bouts, while there were no differences for 90%BFR (P > 0.05). Conclusions: Submaximal running with BFR induced similar responses as maximal running without, despite large differences (i.e., <=30%) in running speed.  Kulcsszavak: blood flow restriction, males, muscle oxygenation, occlusion, running