Introduction: We examined gender differences for performance and surface electromyograms (sEMG) of knee extensors 1hr after downhill running.Methods After downhill running, MVIF deficits were similar (males: 11.7±7.2%, females: 7.5±7.7%) with no changes in endurance times during 50%MVIF. After the downhill run, there was a trend in females, but not males, of an increased ratio for the root mean square (RMS) values of the VL and VM muscles during MVIF testing by 23% (P=0.054). After the downhill run, females, but not males, lowered during 50%MVIF the change in RMS for VM from 48±32% to 30±31% and for VL from 36±23% to 21±18% (P<0.05). For males, a trend was observed for the change in median frequency in VL during 50%MVIF (P=0.05). After downhill running, females, altered the vastus medialis and vastus lateralis contributions to maximal isometric force production and the activity pattern of these muscles during submaximal isometric fatigue.Conclusion: Acute neuromuscular adaptations after downhill running occur during voluntary isometric contractions of knee extensor muscles in females, but not in males.