Lactate
The misunderstood molecule. For decades, lactate was blamed for muscle burn and fatigue. The truth: lactate is a valuable fuel, not a waste product. During exercise, fast-twitch fibers produce lactate, which slow-twitch fibers and the heart then burn. The brain actually prefers lactate over glucose during exercise. Lactate also signals beneficial adaptations and increases BDNF. The "lactic acid causes soreness" myth has been debunked—lactate is cleared within an hour of exercise.
Lactate Myths vs Reality
Old Myths
- • ❌ "Lactic acid" causes muscle burn
- • ❌ Lactate causes muscle soreness
- • ❌ It's a dead-end waste product
- • ❌ Need to "clear" lactate
- • ❌ Fatigue is from lactate buildup
Current Understanding
- • ✓ Lactate is a valuable fuel
- • ✓ Cleared within 60 min post-exercise
- • ✓ Shuttles between cells and organs
- • ✓ Brain and heart love it
- • ✓ Signals beneficial adaptations
Lactate Functions
Fuel Source
Oxidized in mitochondria. Produces 16-18 ATP. Major fuel for heart and brain.
Lactate Shuttle
Fast-twitch produces, slow-twitch consumes. Muscle-to-muscle. Muscle-to-heart.
Gluconeogenesis
Liver converts to glucose (Cori cycle). Recycles carbon. Maintains blood sugar.
Brain Fuel
Astrocytes → neurons. Brain prefers lactate during exercise. Mental clarity.
Signaling Molecule
Binds HCAR1 receptor. Increases BDNF. Triggers adaptations. Exercise signal.
pH Buffering
Actually helps buffer acid. Lactate production consumes H+. Protective effect.
Lactate and Exercise
Lactate Threshold
Intensity where production exceeds clearance (~4mM). Key training zone. Can be improved.
Training Adaptations
- • More mitochondria = better clearance
- • More MCT transporters
- • Higher lactate threshold
- • Better fuel utilization