Rapid method to identify the boundary speed for metabolic stability from race performances.

Develop and validate a rapid method for estimating metabolic stability from race performances. Nineteen runners (12 male, 7 female) provided ≥1 race times for distances from 1.5 to 42 km. Race times were used to estimate the boundary speed for metabolic stability (MSlim) from six regression equations. Twelve males ran for 5-min at a self-selected speed between 60-90% of the estimated MSlim. Seven females ran for 5-min at 90% and 110% of estimated MSlim. Oxygen uptake (V̇O2) was measured and the slope of the line describing the final two minutes of gas sampling was used to quantify metabolic stability. Runners self-selecting speed (79 ± 10% of estimated MSlim) exhibited metabolic stability (zero slope; p = 0.88) with a mean 2-min change in V̇O2 of 35 ± 28 mL/min. Runners at 90% of estimated MSlim also exhibited metabolic stability (zero slope; p = 0.31) with a mean 2-min change in V̇O2 of 66 ± 43 mL/min. Respiratory exchange ratios were <0.90, also consistent with steady state metabolism. Metabolic stability was not possible at 110% of MSlim. A rapid method for estimating the boundary speed for MSlim from race performances is provided for when more extensive metabolic testing is not possible.