Changes in muscle power and neuromuscular efficiency after a 40-minute downhill run in veteran long distance runners

Objective: To 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. Setting: University of Cape Town, Sports Science Institute of South Africa. Participants: Twenty 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. Intervention: A 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 Measures: The 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 (Delta) 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. Results: There was a significant curvilinear relationship between the Delta neuromuscular efficiency and total kilometers raced (R-2 = 0.53, p < 0.05), and a significant inverse relationship between Delta 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. Conclusions: Runners who have raced an accumulated distance of > 5,000 km show a significant dissociation in the Delta neuromuscular efficiency after a downhill run, compared with less experienced runners. Although possible causes for the dissociation are discussed, further research is needed.