Lactate: fuel, blood measurements and exercise

Lactate is not simply waste

Lactate can move between tissues, be used for energy and contribute to glucose production. The term “lactate shuttle” describes this exchange. The liver’s role in making glucose should not be confused with treating every tissue as an identical site of lactate oxidation. Brooks, 2018.

Working muscles can take up lactate while also releasing it. A tracer study in six men during cycling demonstrated this simultaneous exchange. A blood concentration therefore does not directly tell you the total amount produced by a particular muscle. Stanley and colleagues.

Interpreting a blood value

Blood lactate reflects the balance of appearance and removal at the time of sampling. Exercise intensity, protocol and sample timing affect its interpretation. There is no universal rule that easy running equals 2–3 mmol/L, or that every HYROX^® station must reach 8–12 mmol/L.

For testing, examine the pattern across a controlled protocol rather than labelling one number “good” or “bad”. See lactate threshold for the distinction between a fixed concentration and an individually assessed marker.

Fatigue and muscle soreness

Do not reduce all fatigue or burning sensations to a lactate level. Lactate is part of metabolism, not a stopwatch that determines when you can resume running. Nor is next-day soreness evidence of lactate remaining in your muscles.

In a study comparing level and downhill running, delayed soreness occurred after downhill running without the lactate rise seen during level running. This contradicted the claim that lactate accumulation causes delayed-onset muscle soreness. Schwane et al., 1983. A fixed “all lactate disappears after 30–60 minutes” rule is unnecessary and misleading because lactate continues to be produced and used.

Practical relevance

Use controlled station-to-run practice to observe how pacing affects your next run, rather than trying to generate the highest possible lactate reading. This is a practice suggestion, not proof that one session specifically increases lactate clearance or guarantees faster transitions.

Questions

Is lactate produced only without oxygen?

No. Lactate is formed and used under aerobic conditions as well.

Does lactate cause next-day soreness?

No. Delayed-onset soreness should not be explained as lactate trapped in the muscles.

Should I keep every workout below 4 mmol/L?

No. That value is used in some testing conventions, but it is not a universal personal threshold or a target for every training session.