Objetivo: Testar a variação no LAn, detectado por modelos matemáticos e de inspeção visual, quando empregado ergoespirômetro de baixo custo e destinado à aplicação clínica.

Background: Many methods are used for determining the Anaerobic Threshold (AT) by means of sophisticated ergospirometer. Objective: To test the AT variation, detected by mathematical models and visual inspection, when low cost ergospirometer is used and intended for clinical application. Methods: Seventy nine apparently healthy subjects were volunteers in this study; from these, 57 men. The VO2max and the ventilatory threshold were determined by indirect, open-circuit calorimetry. The electro-enzymatic method was used for analyzing the lactacidemia and direct determination of the Lactate Threshold (LT). The AT was determined by two mathematical methods (MM RSS and MM slope ), based on the gases exchange, and by the log-log visual method, for determining the LT. Two independent investigators determined the AT through visual inspection of three graphs, considering two methods (AT -a = V-slope, EqV; and AT -b = V-slope, EqV and ExCO 2 ). The data were analyzed by means of parametric statistics for determining the differences between AT-a versus ExCO2, MMRSS and MMslope; AT-b versus MMRSS and MMslope; and LT versus AT -a , AT -b , MM RSS and MM slope . Results: The MM slope was the only method that presented a significant difference between the AT -a and AT -b (p=0.001), with CV% >15. LT versus MMslope did not present significant difference (p=0.274), however, it was observed a high CV (24%). Conclusion: It was concluded that with the low cost equipment, the MM RSS and AT -a methods can be used for determining the TAn. The MM slope method did not present satisfactory precision to be employed with this equipment. (Arq Bras Cardiol 2010; 95(3) : 354-363)