The anaerobic threshold: 50+years of controversy

The anaerobic threshold (AT) remains a widely recognized, and contentious, concept in exercise physiology and medicine. As conceived by Karlman Wasserman, the AT coalesced the increase of blood lactate concentration ([La-]), during a progressive exercise test, with an excess pulmonary carbon dioxide output (V?CO2). Its principal tenets were: limiting oxygen (O-2) delivery to exercising muscle -> increased glycolysis, La- and H+ production -> decreased muscle and blood pH -> with increased H+ buffered by blood [HCO3-]-> increased CO2 release from blood -> increased V?CO2 and pulmonary ventilation. This schema stimulated scientific scrutiny which challenged the fundamental premise that muscle anoxia was requisite for increased muscle and blood [La-]. It is now recognized that insufficient O-2 is not the primary basis for lactataemia. Increased production and utilization of La- represent the response to increased glycolytic flux elicited by increasing work rate, and determine the oxygen uptake (V?O2) at which La- accumulates in the arterial blood (the lactate threshold; LT). However, the threshold for a sustained non-oxidative contribution to exercise energetics is the critical power, which occurs at a metabolic rate often far above the LT and separates heavy from very heavy/severe-intensity exercise. Lactate is now appreciated as a crucial energy source, major gluconeogenic precursor and signalling molecule but there is no ipso facto evidence for muscle dysoxia or anoxia. Non-invasive estimation of LT using the gas exchange threshold (non-linear increase of V?CO2 versus V?O2) remains important in exercise training and in the clinic, but its conceptual basis should now be understood in light of lactate shuttle biology.

Automated summary

The anaerobic threshold (AT) is a controversial concept in exercise physiology and medicine, originally thought to be caused by muscle anoxia but now understood to be a response to increased glycolytic flux. Lactate is now appreciated as an important energy source and signaling molecule, with non-invasive estimation of LT using the gas exchange threshold remaining important in exercise training and in the clinic.