Anaerobic Threshold

What “anaerobic threshold” means

“Anaerobic threshold” is used for several transition concepts in incremental exercise, but it is not one universally defined switch from aerobic to anaerobic metabolism. Lactate production and oxidation occur across exercise intensities, and energy systems contribute together. A review of more than 50 years of controversy recommends distinguishing the measured phenomenon and method instead of assuming one threshold.

Terms such as first lactate threshold, second lactate threshold, ventilatory thresholds, maximal lactate steady state and critical speed describe related but non-identical constructs. OBLA is a fixed blood-lactate criterion, commonly 4 mmol/L; it is not automatically an individual's physiological threshold. The review by Faude and colleagues compares these different concepts and their validity.

Lactate and fatigue

Rising blood lactate reflects the balance between lactate appearance and disposal. Lactate is also transported and used as fuel. It should not be described as a waste product that directly floods muscle, causes acidosis and makes fatigue begin at a single concentration. The lactate review by Halestrap and Cairns explains why that traditional account is incomplete.

Measurement

A valid result must name the protocol and outcome. Serial blood samples during a graded test can identify a chosen lactate turn point; respiratory-gas testing can identify ventilatory thresholds. Different definitions may return different intensities. A fixed 4 mmol/L result, a heart-rate deflection, a talk test and a 30-minute field effort are not interchangeable measurements.

Heart rate, pace or power associated with a laboratory result may help guide later sessions when conditions are comparable. They remain estimates affected by test mode, protocol, environment, fatigue and individual response. There is no universal threshold at 80–90% of maximum heart rate or 75–85% of VO2max.

HYROX^® application

The current HYROX^® Singles rulebook defines eight 1 km runs and eight fixed stations; it does not prescribe an anaerobic-threshold pace. A measured running threshold may inform pacing, but sleds, carries, lunges and wall balls impose different mechanical and local muscular demands. Station labels alone cannot establish whether an athlete is above a metabolic threshold.

Tempo work and intervals can be programmed near a measured transition, but duration, recovery and weekly frequency must fit the athlete and total load. Research on endurance-training intensity distributions does not establish a mandatory 80/20 split for every HYROX^® athlete. A 2025 individual-participant meta-analysis found that outcomes differed with training status and the compared models.

Questions

Is anaerobic threshold the same as a lactate threshold?

The terms are sometimes used together, but several lactate and ventilatory threshold definitions exist. State the test and criterion rather than treating them as one interchangeable value.

Does 4 mmol/L identify my threshold?

Four mmol/L is a conventional fixed OBLA criterion. It may be useful within a consistent protocol, but it is not automatically an individual's maximal steady state or unique threshold.

What threshold pace should I use for HYROX^®?

No universal pace or heart-rate percentage applies. Use a clearly defined test, interpret it with the test protocol and combine it with race-task practice and current training load.

Dial in your threshold pacing with Repz - data-driven training for HYROX^® athletes.