Abstract
Blood lactate concentration ([La(-)](b)) is one of the most often measured parameters during clinical exercise testing as well as during performance testing of athletes. While an elevated [La(-)](b) may be indicative of ischemia or hypoxemia, it may also be a "normal" physiological response to exertion. In response to "all-out" maximal exertion lasting 30-120 seconds, peak [La(-)](b) values of approximately 15-25 mM may be observed 3-8 minutes postexercise. In response to progressive, incremental exercise, [La(-)](b) increases gradually at first and then more rapidly as the exercise becomes more intense. The work rate beyond which [La(-)](b) increases exponentially [the lactate threshold (LT)] is a better predictor of performance than V O2max and is a better indicator of exercise intensity than heart rate; thus LT (and other valid methods of describing this curvilinear [La(-)](b) response with a single point) is useful in prescribing exercise intensities for most diseased and nondiseased patients alike. H(+)-monocarboxylate cotransporters provide the primary of three routes by which La(-) transport proceeds across the sarcolemma and red blood cell membrane. At rest and during most exercise conditions, whole blood [La(-)] values are on average 70% of the corresponding plasma [La(-)] values; thus when analyzing [La(-)](b'), care should be taken to both (1) validate the [La(-)](b)-measuring instrument with the criterion/reference enzymatic method and (2) interpret the results correctly based on what is being measured (plasma or whole blood). Overall, it is advantageous for clinicians to have a thorough understanding of [La(-)](b) responses, blood La(-) transport and distribution, and [La(-)](b) analysis.