ObjectiveTo determine whether oxygen consumption during submaximal running increases in proportion to years of accumulated training and racing in masters runners after a bout of downhill running.SettingUniversity of Cape Town, Sports Science Institute of South Africa.ParticipantsSeventeen male masters distance runners (45–55 years) with a range of training (3,536 km to 79,320 km) and racing (205 km to 12,218 km) experience.InterventionA 40-minute continuous treadmill run, at 70% of peak treadmill running speed, consisting of two horizontal runs of 10 minutes each, separated by a 20-minute downhill (−10%) run.Main Outcome MeasuresHeart rate and oxygen consumption were measured continuously during the run. Data were analyzed to identify correlations between the end of the first horizontal section (minute 10) and the first minute of the second horizontal run (minute 31). Delta values were related to current training mileage (km/wk), total accumulated racing distance (km), and total accumulated training distance (km).ResultsThere were significant changes in both heart rate (p < 0.001) and oxygen consumption (p < 0.001) over time during the 40-minute run. There were no significant relationships between the change in oxygen consumption (delta) between minute 10 and minute 31 and total accumulated training mileage, total accumulated racing mileage, and current training.ConclusionsThe results of this study suggest either that submaximal oxygen consumption is not a sensitive marker of changes in neuromuscular activity or that the downhill protocol did not impose a sufficient eccentric stress for the subjects.