Glycolytic & aerobic System, interacting with each other
In essence Lactate Production Rate and Lactate Oxidation Rate describe the interaction of glycolytic and aerobic metabolism. Lactate Production Rate describes the gross rate at which lactate is produced through glycolytic metabolism. This lactate can then be used as a preferred fuel source in the aerobic system, which defines the Lactate Oxidation Rate.
Both are rates rather than blood lactate concentrations. One describes how quickly lactate is produced; the other describes how much lactate the oxidative system can potentially utilize at a given exercise intensity. Lactate is the central link that connects the glycolytic metabolism with the aerobic metabolism.
Two flux rates across exercise intensity
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Lactate Production Rate, The Glycolytic Flux
Lactate Production Rate describes how much lactate is produced per minute through glycolytic metabolism.
This rate is highly relevant for sports performance because of two aspects:
- lactate can only be produced out of carbohydrates, and carbohydrates when used as a fuel always become lactate during the process. Therefore there is a direct and proportional link between lactate production rate and glucose utilization rate.
- Lactate production is directly connected to ATP production. This means: the lactate production rate is also a proxy of glycolytic energy production rate.
If you know the glycolytic lactate-production flux, you gain information about how quickly carbohydrate is being used and how much ATP is being supplied through glycolysis.
One glucose through glycolysis, then the rate
Net, from blood glucose. Starting from muscle glycogen, glycolysis nets 3 ATP.
Lactate Oxidation Rate, aerobic fuel demand
Lactate Oxidation Rate describes the potential rate at which lactate can be utilized through oxidative metabolism. The aerobic metabolism needs fuel, and lactate is the preferred form of fuel. Therefore: the higher the rate of the aerobic metabolism the more lactate can be used as a fuel.
Intrinsically athletes and coaches know that keeping the aerobic metabolism running at a higher rate helps with lactate combustion, this is the very reason why we do low intensity aerobic work for cool down and recovery phases in between intervals. This is one reason active recovery is so familiar to coaches and athletes. Maintaining an appropriate level of aerobic metabolism after a hard effort can increase lactate utilization compared with complete rest.
Lactate Oxidation Rate therefore describes an intensity-dependent ceiling for how much lactate the oxidative system can potentially process.
The oxidative flywheel and the ceiling it sets
Three states that tell a story about performance
The interaction of lactate production, and thereby carbohydrate combustion and glycolytic ATP production, with the aerobic metabolism has three distinct states which are all relevant for performance.
Lactate Clearance Capacity
When the potential Lactate Oxidation Rate is greater than the current Lactate Production Rate, the oxidative system has capacity available to utilize additional lactate.
This becomes particularly relevant after a high-intensity effort, attack or interval in which lactate has accumulated. The larger the available difference between possible lactate combustion and gross lactate production, the greater the potential capacity to deal with previously accumulated lactate.
This is the physiological relationship behind Lactate Clearance Rate: clearance depends not only on the ability to oxidize lactate, but also on how much lactate is still being produced while the athlete is recovering at lower intensity.
Lactate Oxidation Rate shows the potential to remove. Lactate Production Rate shows how much of that capacity is already occupied.
Available clearance capacity, below the crossing
Net Lactate Accumulation Rate
Above the point where Lactate Production Rate exceeds Lactate Oxidation Rate, the balance reverses. More lactate is being produced than can be oxidized, and lactate begins to accumulate.
The difference between the two fluxes provides the metabolic basis for Lactate Accumulation Rate. As the gap grows with increasing exercise intensity, net accumulation becomes faster.
Net accumulation, above the crossing
The Balance Point: MLSS
Between clearance and accumulation lies the point at which Lactate Production Rate and Lactate Oxidation Rate are in balance.
This intersection of lactate production rate and possible lactate combustion rate provides the physiological framework for maximal lactate steady state: the highest exercise intensity at which lactate appearance and utilization are balanced. In other words: at this intensity the aerobic metabolism is saturated with lactate, no additional lactate can be combusted but also no additional lactate is accumulating. A perfect balance.
MLSS is not an isolated threshold value. It is the result of the balance of lactate production and combustion.
The crossing, and what a constant load does either side of it
One Pair of Curves, Multiple Performance Metrics
Lactate Production Rate and Lactate Oxidation Rate provide the underlying context for several relevant metrics. Carbohydrate Combustion rates. Glycolytic ATP production rate, possible lactate clearance or accumulation and even maximum lactate steady state.
Instead of looking at lactate concentration, threshold, clearance and accumulation as unrelated outputs, the production-and-oxidation framework connects them through the one coherent framework, based on the metabolism of the athlete.
One pair of curves, four consequences
Explore other INSCYD metrics.
What the spare capacity below the crossing is worth after a hard effort.
Read more Anaerobic Threshold (MLSS)The crossing itself: the highest intensity the two fluxes still balance at.
Read more Accumulation IndexWhat happens above the crossing, when production runs past what can be oxidized.
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