Plasma lactate concentration increases as a parabola with delay during ramp exercise

Area of Science:

• Exercise Physiology
• Biophysics
• Metabolic Modeling

Background:

• Plasma lactate concentration ([La-]) is a key indicator of metabolic stress during exercise.
• Understanding the kinetics of lactate accumulation is crucial for interpreting exercise responses.
• Previous models often simplify the complex relationship between exercise intensity and lactate dynamics.

Purpose of the Study:

• To develop and validate an elementary mathematical model for plasma lactate concentration during ramp exercise.
• To investigate the relationship between the rate of lactate accumulation and plasma lactate levels.
• To explore the concept of a kinetic delay in lactate accumulation during incremental exercise.

Main Methods:

• Development of a parsimonious system model assuming linear increase in lactate accumulation rate (Rc) with a time delay (delta).
• Assumed constant volume of the extramuscular distribution space (S).
• Validation of the model against plasma [La-] data from five healthy subjects during cycle ergometer ramp exercise (1 W/2 s).

Main Results:

• The model accurately describes plasma [La-] changes during ramp exercise (r > 0.99) with minimal residuals.
• Plasma [La-] was shown to increase parabolically with time, influenced by the kinetic delay (delta).
• The model supports hypotheses regarding the anaerobic threshold or coupled increases in lactate appearance and disappearance rates.

Conclusions:

• An elementary model effectively captures plasma lactate dynamics during ramp exercise.
• A kinetic delay in lactate accumulation is a significant factor in plasma lactate response.
• Plasma lactate may reflect muscle metabolic events with a delay during incremental exercise.