Is reaction time altered by mental or physical exertion?

Area of Science:

• Human physiology
• Motor control
• Sports science

Background:

• Reaction time is crucial in daily activities and sports.
• Previous research suggests fatigue negatively affects reaction time.
• The specific impact of mental vs. muscle fatigue on reaction time components is not fully understood.

Purpose of the Study:

• To investigate the effects of mental and muscle effort on reaction time and its components: premotor time and electromechanical delay (EMD).
• To differentiate the contributions of mental and muscle fatigue to changes in reaction time.

Main Methods:

• Thirteen participants underwent three conditions: mental effort (mathematical task), muscle effort (biceps contractions), and a control (documentary).
• Reaction time, premotor time, and EMD were measured before and after each condition during voluntary biceps contractions.
• EMD was also assessed during evoked contractions to isolate force onset and muscle motion components.

Main Results:

• Reaction time and premotor time showed no significant changes across all conditions.
• Electromechanical delay (EMD) increased significantly only after the muscle effort condition (+17% in evoked contractions, P=0.001).
• The increase in EMD was mainly attributed to the passive series elastic component.

Conclusions:

• Neither mental effort nor muscle exertion negatively affects simple reaction time during voluntary contractions.
• Muscle effort, however, does lead to a significant increase in electromechanical delay, suggesting a specific impact on muscle contractile properties rather than neural processing time.