PREDICTION OF NORMAL VALUES FOR LACTATE THRESHOLD ESTIMATED BY GAS-EXCHANGE IN MEN AND WOMEN

Lactate threshold (LT) is an index of exercise capacity and can be est imated from the gas exchange consequences of a metabolic acidosis (LTG E) In recent pears, it has emerged as a diagnostic tool in the evaluat ion of subjects with exercise limitation. The purpose of this study wa s to develop LTGE prediction equations on a relatively large sample of adults and to cross-validate each equation. A total of 204 healthy, s edentary, nonsmoking subjects (103 men and 101 women), aged 20-70 year s, underwent graded exercise testing on a cycle ergometer. The V-slope technique was used to detect LTGE as the oxygen uptake (VO2) at the b reakpoint of the carbon dioxide output versus VO2 relationship. Multip le linear regression was used to develop 12 equations with combination s of the following predictor variables: age, height, body mass, and fa t-free mass. Eight of the equations are gender-specific and four are g eneralized with gender as a dummy variable. The equations were cross-v alidated using the predicted residual sum of squares (PRESS) method. T he results demonstrate that the equations had relatively high multiple correlations (0.577-0.863) and low standard errors of the estimate (0 .123-0.228 l . min(-1)). The PRESS method demonstrated that the equati ons are generalizable, i.e., can be used in future studies without a s ignificant loss of accuracy. Since we tested only healthy, sedentary s ubjects, our equations can be used to predict the lower limit of norma l for a given subject. Using individual data for healthy and diseased subjects from the literature, we found that our gender-specific equati ons rarely miscategorized subjects unless they were obese and mass was a predictor variable. We conclude that our equations provide accurate predictions of normal values for LTGE and that they are generalizable to other subject populations.