ObjectiveTo establish whether there was a relationship between the total accumulated distances of racing in veteran runners and the neuromuscular efficiency of the quadriceps muscles before and after a downhill run.SettingUniversity of Cape Town, Sports Science Institute of South Africa.ParticipantsTwenty male veteran long distance runners (45–50 years of age) with a range of training (1,300 km to 111,280 km) and racing (0 km to 9,737 km) experience.InterventionA 40-minute downhill run (−10% decline) on a treadmill, at a speed corresponding to 70% of the subject's peak treadmill running speed.Main Outcome MeasuresThe difference between integrated electromyography (IEMG)/mean force over a 5 s maximal voluntary isometric contraction before and after the downhill run was calculated as the delta (&Dgr;) neuromuscular efficiency. This was related to the total kilometers trained, current training distance, total kilometers raced, and number of races > 56 km. The difference in drop jump height before and after the downhill run was measured as well as changes in heart rate throughout the run.ResultsThere was a significant curvilinear relationship between the &Dgr; neuromuscular efficiency and total kilometers raced (R2= 0.53, p < 0.05), and a significant inverse relationship between &Dgr; neuromuscular efficiency and the number of races > 56 km (r= −0.50, p < 0.05). Drop jump height decreased after the downhill run, and heart rate increased during the run.ConclusionsRunners who have raced an accumulated distance of > 5,000 km show a significant dissociation in the &Dgr; neuromuscular efficiency after a downhill run, compared with less experienced runners. Although possible causes for the dissociation are discussed, further research is needed.