ABSTRACT
Anaerobic threshold (AT) has been defined in several ways, with the most accepted definition being “that point at which blood lactate begins to increase beyond the basal level.” This definition implies that AT is determined through analysis of a series of blood samples taken as the exercise or work bout progresses. Some purists might argue that lactic acid accumulation should be examined in the muscle, rather than waiting for lactate to appear in the blood. At the other end of the spectrum, are the noninvasive measurement advocates who recommend that AT be defined by changes in respiratory parameters. The most commonly observed respiratory parameter used to determine AT is the non-linear increase in pulmonary ventilation. Software programs are available to predict AT from respiratory parameters, or the respiratory data can be plotted and determined by fitting two lines to the data and looking at their intersection point (Figure 1). There are inaccuracies associated with the graphical analysis of respiratory parameters, but such a method is much less risky than one requiring blood sampling. AT is normally reported as a percentage of VO2max.
