Lactate: Neither a Hero Nor a Villain...
...But Ever-Present and Context-Dependent
Lactate is a love-hate story for me. It made me suffer during grueling interval training sessions, both in running and, even worse, in cross-country skiing—my arms would burn, my cheeks would flush, and I'd have a fierce urge to quit everything! Then, at 23, it tormented me again during a Master's project that I knew was doomed to fail. Still, I couldn’t contradict "the boss," who kindly welcomed me into her functional and respiratory exploration department at the Grenoble University Hospital, even though I was just a sports student curious about how to train better: the magic of natural but well-calibrated training for me!
The task was to detect the lactate threshold by measuring blood pH from a fingertip. At the time (1984), during the frenzy over aerobic and anaerobic thresholds (2 mM at VT1 and 4 mM at VT2), we didn’t have portable lactate analyzers that could deliver results in under 2 minutes with just 0.3 µL of blood. The body's buffering system is so efficient that detecting the lactate threshold through pH changes, which stays near a neutral value of 7.4, is impossible.
To combat acidosis, the body employs local and systemic buffers. Locally, ionizable molecules fix or release H+ ions as pH changes, dampening shifts in the acid-base balance—this is the buffering effect. An ionizable molecule is a more effective buffer if it captures protons during acidification and releases them during alkalinization. Many biological systems accumulate small ionizable molecules with a pKa near 7, whose properties are stable regardless of their ionization state. In mammals, the primary plasma buffer consists of free phosphate groups.
Example: The Body’s Resilience
Thankfully, as athletes, our sessions don’t exceed the buffering capacity of our bodies!
Back then, I was mostly trying to "do less but better" to have time for studying and living beyond sports (friends, a boyfriend, and music-filled nights in a “Spanish inn” with parties that ended in races aimed at "metabolizing" the tequila-banana shots I barely sipped, as I didn’t like alcohol—except my homemade genepi liqueur, which risked some perilous climbs in the Écrins massif).
At 25, I took the train to Paris to attend a major conference on aerobic and anaerobic thresholds at INSEP. There, a revelation struck me, shaping my entire life. A raised hand belonged to an older gentleman, Albert-Paul Chassain (APC), who wasn’t part of the trendy researcher panel. He dared to ask a contentious question:
"What if lactate depends on time, and it’s impossible to measure the lactate threshold using just a short incremental protocol with 2- to 4-minute stages?"
Chassain, nicknamed APC at the Limoges University Hospital where he worked, never published his ideas. Despite his shyness, he had parachuted into the French resistance from England at age 16. At the coffee break, I approached him, convincing him to supervise my PhD on this idea: determining the critical lactate power, which George Brooks was simultaneously describing as the maximal lactate steady-state (MLSS) in the U.S. Communication between researchers was still face-to-face, and journal articles were locked behind expensive subscriptions.
Fast-forward, I secured a PhD scholarship in Grenoble and crossed the Massif Central in my Citroën 2CV to Limoges. With no accommodation, I slept in my car for two weeks until a kind soul—founder of the famous "Gendarmes and Thieves" race—offered me a nursery room in his home while I awaited funding.
This experience resonates with the challenges faced by my international students today in the Paris-Saclay International Master's program, with added bureaucracy and glamorous trips to the prefecture for paperwork.
The Nuanced Role of Lactate in Exercise Physiology
For decades, lactate was at the center of a debate: Is it a "bad boy" responsible for muscle fatigue or a "good boy" providing energy for athletic performance? Recent discoveries reveal that lactate is neither hero nor villain but an omnipresent byproduct of metabolism, with context-dependent functions. Let’s explore its misunderstood nature.
The Traditional Misconception: Lactate as the "Bad Boy"
Blamed for Fatigue:
Lactate was thought to lower muscle pH (acidosis), impairing enzymatic functions and muscle contractions.
Its accumulation was linked to the burning sensation during intense exercise.
Linked to Muscle Soreness (DOMS):
Incorrectly associated with delayed onset muscle soreness, though evidence points to microscopic muscle tears as the cause.
Fear of the Lactate Threshold:
Crossing the lactate threshold, where production exceeds elimination, was seen as a critical limit after which performance would decline.
Lactate's Redemption: The "Good Boy" Perspective
Recent advancements highlight its essential roles:
Energy Substrate:
Lactate is a key fuel for the heart and slow-twitch muscle fibers during prolonged exercise.
Through the Cori cycle, lactate is converted back into glucose in the liver, replenishing energy stores.
Lactate Shuttle & Work Capacity:
The “lactate shuttle” redistributes lactate between tissues for oxidation and gluconeogenesis.
Signaling Molecule:
Lactate triggers pathways promoting mitochondrial biogenesis, crucial for endurance training adaptations.
Angiogenesis:
Lactate supports the formation of new blood vessels, enhancing oxygen delivery to muscles.
Practical Applications: Training with MLSS
The Maximal Lactate Steady-State (MLSS) represents the highest intensity where lactate production and elimination are balanced. Training at this level optimizes endurance performance by maintaining a "homeostatic" effort without excessive lactate buildup.
Example Session:
Warm-Up: 10 minutes at low intensity (RPE 10-11).
Main Set: 20–30 minutes alternating every 2 minutes:
Slightly above MLSS (RPE 15).
Slightly below MLSS (RPE 13).
Cool-Down: 10 minutes at low intensity.
Conclusion
Lactate is an adaptive molecule, and its effects depend on exercise and recovery contexts. Proper training that masters RPE at MLSS can leverage lactate’s dual roles as an energy source and signaling molecule.
Let’s embrace the Dr. Jekyll side of lactate, leaving the Mr. Hyde misconceptions behind. With robust training principles, simplicity in execution, and careful lactate monitoring, you can progress without exhaustion. 😊
