Lactate Accumulation Rate - in One single Number
The Accumulation Index is a normalized benchmark that describes how quickly lactate accumulates once exercise intensity exceeds maximal lactate steady state (MLSS). It summarizes the steepness of the net lactate-accumulation rate at exercise intensities above anaerobic threshold on a scale from 0 to 100.
This is performance relevant because an athlete has an individual, training-state-dependent maximal lactate concentration. The faster lactate accumulates, the faster the athlete approaches that physiological limit and, consequently, exhaustion.
The Accumulation Index turns the rate at which an athlete approaches exhaustion at high intensity exercise into one directly comparable benchmark.
Net lactate accumulation above MLSS
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Comparison between athletes and sports
Lactate Accumulation Rate can be represented as a curve showing how net lactate accumulation changes with increasing exercise intensity. The Accumulation Index reduces this relationship to one practical number.
Because the index is normalized to metabolic load rather than to discipline-specific power or speed, it allows coaches and practitioners to compare accumulation characteristics across different athletes and even sports. A cyclist and a runner can have very different external performance values while still showing a comparable physiological accumulation characteristic.
Instead of overlaying curves and correcting for multiple performance variables, the Accumulation Index provides one standardized value for comparison.
Different inputs, one normalized characteristic
Time to exhaustion
The speed of lactate accumulation at high intensity matters because it determines how quickly the athlete moves toward the individual maximal lactate concentration at exhaustion.
For two athletes with the same maximal lactate concentration, a higher Accumulation Index indicates that this limit is approached more quickly. Conversely, a lower Accumulation Index indicates slower net accumulation and therefore more time before the same lactate limit is reached at the relevant relative load.
This makes the Accumulation Index particularly useful for understanding performance above MLSS: it condenses the athlete’s accumulation behavior into a single number that can be tracked and compared.
Time to the individual lactate limit
Index and limit values illustrative.
Lactate accumulation is strongly linked to MLSS and VO₂max: As MLSS marks the highest intensity at which lactate production and lactate utilization can remain in equilibrium; net lactate accumulation starts only above this intensity.
When MLSS lies closer to VO₂max, accumulation begins at a higher %VO₂max and therefore the net accumulation becomes steeper and the Accumulation Index higher.
VO₂max and MLSS therefore provide the physiological context behind the Accumulation Index: the index shows how fast accumulation occurs, while these metrics help explain why.
MLSS, VO₂max and the steepness between them
Explore other INSCYD metrics.
MLSS marks the highest intensity at which lactate production and lactate utilization can remain in equilibrium; net lactate accumulation starts only above this intensity.
Read more VO₂maxWhen MLSS lies closer to VO₂max, accumulation begins at a higher %VO₂max and therefore the net accumulation becomes steeper and the Accumulation Index higher.
Read more Aerobic & Anaerobic Energy ContributionHow much of the energy at a given intensity is delivered aerobically, and how much through glycolysis.
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