Purpose: To establish the typical error (TE) associated with equipment, testing, and biological variation of a running economy (RE) test in 11 elite male distance runners ([latin capital V with dot above]O2max 70.3 +/- 7.3 mL[middle dot]min-1[middle dot]kg-1), and measure the between-athlete variation of 70 highly trained runners ([latin capital V with dot above]O2max 69.7 +/- 6.0 mL[middle dot]min-1[middle dot]kg-1) to determine the magnitude of the smallest worthwhile change (SWC) required for RE. Methods: Runners performed three 4-min bouts of submaximal treadmill running at speeds of 14, 16, and 18 km[middle dot]h-1 (0% grade), on two separate occasions within a 7-d period to determine reliability and once over a 3-yr period to measure the SWC. During all RE tests O2 consumption ([latin capital V with dot above]O2), ventilation ([latin capital V with dot above]E), respiratory exchange ratio (RER), heart rate (HR), stride rate (SR), and concentration of blood lactate (Lac) were determined. Results: The TE for the pooled data of three running speeds (14, 16, and 18 km[middle dot]h-1) was 2.4% for [latin capital V with dot above]O2, 7.3% for [latin capital V with dot above]E, 27% for Lac, and ranged between 1 and 4% for RER, HR, and SR. Conclusions: The results demonstrate that although the magnitude of the TE for a submaximal treadmill running protocol of three 4-min work efforts is small (2.4-7.3%) for measures associated with cardiorespiratory parameters, it is three- to fourfold higher for Lac. Given the small TE associated with RE, and a SWC of similar magnitude for this cohort of distance runners, the RE test is useful in detecting changes attributable to training interventions. Changes in RE greater than ~2.4% in this cohort of elite distance runners are likely to be "real" and "worthwhile," and not simply related to testing error and typical variation.
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