Endurance · metabolism · mitochondria

The lactate shuttle

Lactate is neither waste nor a villain. It's fuel — and an honest marker of your effort. Watch mitochondria burn it in live mode, and plan in the lab which training shifts your lactate curve, and how.

Lactate–power curve

Week 0

VLamax 0.55 mmol/l/s · Threshold at 4.5 mmol/L

Active type Week 0 (after training) 4 mmol = just an average

200 W → 1.9 mmol/L Zone 1 · base

80 WProbe the curve460 W

Substrate at this power55% fat · 45% carbs

Glycogen in the test:

Choose a training week

Choose a training week. Watch the curve shift right: at the same power less lactate — that's fitness. Lactate measures this adaptation, it doesn't prevent it.

Adaptations

LT1

150 W

LT2 · MLSS

236 W

VO₂max

323 W

Capillarisation C/F · O₂ transport35%

Mitochondria Density & clearance35%

VO₂max central capacity35%

Glycolytic power VLamax · type II fibres55%

Fatigue slows adaptation0%

Blood lactate

1.0 mmol/L

LT2

Muscle cell · glycolysis → lactate → mitochondrion → ATP

Control

Rest

Easy. Lactate stays low — pure fat burning, barely a stimulus.

RestZone 1LT2VO₂maxSprint

95Watts · 41% of LT2

Training stimulus: none — start the session and find your window.

Body values

LT2 · threshold

236 Watts

Mitochondria

35 % density

Burned as fuel

0 units

Training time

0:00

Breathing & acid–base — same threshold, different windows

Breathing

16 /min

Blood pH

7.40

Talk test

Full sentences

DFA α1 HRV

0.95

Session complete

Your threshold has shifted.

236 Watts LT2