Struggling to stay steady under pressure may not just be “in your head”; researchers found that mental stress can directly affect muscle blood flow and fine motor control during simple physical tasks.
Study: The impact of cognitive stress on vascular response and force steadiness during a handgrip task in males and females. Image credit: VADZIM SHUBICH/Shutterstock.com
Force steadiness during very low-intensity contractions and vascular responses involved in motor-task performance can be reduced under cognitive stress, as reported in a new study published in the Journal of Applied Physiology.
Cognitive pressure affects physical performance
Adequate blood flow to working muscles is essential for meeting the muscles’ energy demands during tasks that involve sustained force, such as a handgrip test. In these tasks, known as isometric contractions, muscles produce force without noticeably changing length or moving the joint. This sustained contraction increases pressure within the muscle, which can restrict blood flow to the active tissue.
Many everyday activities, workplace duties, and military operations require people to perform physical and mental tasks simultaneously. For example, a person may need to maintain steady muscle control while also concentrating under pressure or performing a mentally demanding task. However, researchers still know relatively little about whether cognitive stress influences blood flow and vascular control in working muscles during these types of motor activities.
This study was designed by researchers at the University of Oklahoma, USA, to explore changes in muscle blood flow, force steadiness, and muscle activation during isometric handgrip tasks at varying intensities, with or without a stressful cognitive task.
The research team included both male and female participants, as gender differences may potentially influence the impact of intramuscular pressure on blood flow.
Testing blood flow during stressful motor challenges
The study population included 15 male and 15 female participants who attended two randomized experimental sessions three days apart. In one session, both cognitive and motor tasks were performed simultaneously, whereas in the second session, only the motor task was performed in isolation.
The cognitive task involved difficult mental math, a widely used technique for increasing stress biomarkers. The isometric handgrip task was selected as a motor task in which participants performed isometric contractions at 5 %, 10 %, and 20 % of maximal voluntary contraction.
Forearm vascular conductance, which is a measure of the ease of blood flow through blood vessels relative to pressure, was measured during each isometric contraction. Force steadiness was measured as the amplitude of the force fluctuations following muscle contractions. Acute changes in anxiety during the experimental protocol were assessed using a visual analog scale.
Mental stress reduced blood vessel function during contractions
The study analysis revealed that cognitive stress induced during the mental math test significantly reduced forearm vascular conductance in both males and females. The reduction was greater at lower contraction intensities.
For contractions performed at very low and low intensities (5 % and 10 %), participants with greater maximal voluntary contraction (stronger participants) showed smaller reductions in forearm vascular conductance. In sessions including cognitive tasks, mean arterial pressure increased to a greater extent at lower contraction intensities, and the induction was more pronounced in females.
Regarding force steadiness, the study found a significant reduction in response to cognitive stress only at very low intensity contraction. The reduction was comparable between male and female participants.
The researchers did not observe significant changes in muscle activation patterns measured by electromyography (EMG) during cognitive stress.
Stress may disrupt muscle control and blood regulation
The findings suggest that cognitive stress can impair both muscle control and vascular function during low-intensity handgrip tasks in men and women. The effects were most noticeable during very low-force contractions, where participants showed reduced handgrip steadiness alongside lower forearm vascular conductance.
While the decline in force steadiness was similar across participants, reductions in vascular conductance were greater in individuals with lower maximal voluntary contraction (MVC) values. In this study, these participants were more often women, who, on average, had lower strength levels than men.
Previous research has shown that intramuscular pressure plays an important role in regulating blood flow during isometric contractions performed without cognitive stress. In stronger individuals, higher pressure within the muscle can restrict blood flow even at relatively low contraction intensities, sometimes below 20 % of maximum effort. Consistent with this, the female participants in the current study, who had approximately 43 % lower MVC values than males, showed greater vascular conductance during the motor task alone, particularly at very low contraction intensities.
However, when the motor task was combined with a mentally stressful task, females tended to show larger reductions in vascular conductance at lower contraction intensities. The authors suggest that the greater intramuscular pressure generated by stronger males may partially offset the effects of cognitive stress on blood flow regulation. Still, the researchers emphasize that the mechanisms involved are not yet fully understood.
Earlier studies have reported that cognitive stress can influence muscle sympathetic nerve activity and vascular conductance under resting conditions, although findings have varied by muscle group and population studied. The current findings extend this work by showing that cognitive stress may also alter vascular regulation during active muscle contractions.
Overall, the study highlights the significant contribution of cognitive stress to altering vascular responses and the control of force in both males and females during motor activities.
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