Lactate accumulates in the cerebrospinal fluid after prolonged exercise

Area of Science:

• Neuroscience
• Exercise Physiology
• Metabolic Research

Background:

• The resting brain primarily uses glucose, releasing some lactate.
• During exercise, the brain shifts to extracting lactate, increasing carbohydrate uptake beyond oxygen needs.
• The fate of this excess carbohydrate uptake during sustained exercise remains unclear.

Purpose of the Study:

• To investigate the fate of excess carbohydrate uptake in the brain during sustained exercise.
• To determine if lactate accumulation in cerebrospinal fluid (CSF) explains the increased brain carbohydrate uptake.
• To assess the impact of lactate accumulation on brain energy availability.

Main Methods:

• 13 healthy human participants underwent 2 hours of mixed-intensity cycling exercise.
• Cerebrospinal fluid (CSF) lactate and glucose concentrations were measured before and after exercise.
• Cerebral lactate uptake was correlated with CSF lactate accumulation.

Main Results:

• Exercise induced a shift from brain lactate release to extraction, resulting in excess carbohydrate uptake.
• CSF lactate concentration doubled after exercise, while CSF glucose remained stable.
• Lactate accumulation in CSF correlated with cerebral lactate uptake and represented a 15% increase in carbohydrate-based ATP availability.

Conclusions:

• Sustained exercise leads to significant lactate accumulation in the CSF.
• This lactate accumulation contributes to, but does not fully explain, the excess carbohydrate uptake by the brain during exercise.
• The findings highlight a temporal and material dissociation between brain glucose and oxygen metabolism during sustained physical activity.