Distinct Roles of Dopamine and Noradrenaline in Physical Fatigue

Area of Science:

• Neuroscience
• Exercise Physiology
• Pharmacology

Background:

• Neurotransmitters dopamine (DA) and noradrenaline (NA) are implicated in regulating cognitive and physical functions.
• Their specific roles in exercise performance and fatigue perception remain incompletely understood.
• Acute pharmacological manipulation offers a method to investigate these neurotransmitter systems during fatiguing exercise.

Purpose of the Study:

• To elucidate the distinct roles of dopamine (DA) and noradrenaline (NA) in modulating exercise performance and fatigue.
• To examine the effects of methylphenidate (MPH) and reboxetine (REB) on physiological, subjective, and performance outcomes during fatiguing exercise.

Main Methods:

• Triple-blinded randomized crossover study involving 18 healthy adults.
• Participants underwent three conditions: methylphenidate (MPH), reboxetine (REB), or placebo, prior to dynamic leg extensions to exhaustion.
• Behavioral, subjective (e.g., perceived exertion, mood), and physiological (e.g., heart rate, blood lactate) measures were assessed.

Main Results:

• MPH improved perceived vigor and alertness while decreasing sleepiness, but did not significantly alter exercise repetitions or perceived exertion.
• REB significantly reduced the number of leg extension repetitions (exercise performance) without affecting perceived exertion or mood.
• Fatigue was induced in all conditions, confirmed by physiological and subjective markers.

Conclusions:

• Dopamine primarily influences cognitive and perceptual aspects of exercise, enhancing alertness and mood but not physical capacity.
• Noradrenaline negatively impacts exercise performance, reducing repetitions without altering fatigue perception, suggesting a dissociation between capacity and subjective experience.
• These findings highlight differential roles of DA and NA in regulating performance and perception during fatiguing exercise.