Comparison of Behavioral and Cerebral Hemodynamic Responses to Standing and Walking Conditions: A Pilot Study

• ¹ University of Texas at Austin, Kinesiology and Health Education, United States
• ² University of Texas at Austin, Psychology, United States

Purpose/Background There is an increased prevalence of sedentary behaviors, despite the known benefits associated with participation in physical activity (PA). Since sedentary behaviors are associated with higher health risks and reduced cognitive function in later life, examination of physiological responses to light and moderate PA has merit. Even brief bouts of PA such as walking briskly (Hillman et al., 2011), resistance training (Liu-Ambrose et al., 2010), and coordinated movements like sports training (Budde, 2008; Jäger, Schmidt, Conzelmann, & Roebers, 2014), have a positive impact on cognitive performance (Hwang et al., 2017; Tomporowski et al., 2008). The purpose of this study was to determine the behavioral responses of reaction time and accuracy and the oxygenated hemoglobin concentration (HbO2) in the prefrontal cortex during standing and walking conditions that require dual task completion. First, the demands of the conditions were confirmed; then the effects of participation in the two conditions were compared. Methods Twenty-five healthy individuals (Mean age = 22.3, SD = 2.5 years, BMI= 25.2 ± 4.5; 44% female), were recruited to participate in this study. The researchers were unable to secure a clean fNIR signal for four participants and therefore were eliminated from the analysis. Physical Activity Conditions Participants were instructed to stand or walk on a Motek instrumented “V-Gait” treadmill integrated with a 180° virtual reality (VR) projection screen. Each participant wore gloves that had “kinematic-motion capture markers,” which were integrated with the VR screen. The motion of the participants was directly connected with visual and auditory feedback for the conditions. During the conditions, red and green objects appeared at random on the VR screen. The participants were instructed to strike at the red or green objects, depending on the condition, using their motion capture gloves. Participants performed four four-minute PA conditions with varying task complexities; standing congruent, standing incongruent, walking congruent and walking incongruent. During the congruent conditions, the participants were instructed to strike the green objects, not the red objects. During the incongruent conditions, the participants were instructed to strike the red, not the green objects. A VICON motion capture system (Oxford Metrics, Inc., Oxford, UK) related to the Motek “V-Gait” treadmill to record reaction time (RT) and accuracy (# correct) for each of the four PA conditions. Accuracy and RT were measured for each object that appeared on the VR screen and were later averaged together per condition for paired sample t-tests; both standing conditions were averaged together, and both walking conditions were averaged together. Functional near infrared spectroscopy (fNIRS) measurements Measurements of cerebral hemodynamics were performed by using LED-based optical emitters (‘sources’) and receivers (‘detectors’) in conjuncture with NIRScout. The detectors and sources were arranged on the fNIR montage to measure the prefrontal cortex (seven detectors and eight sources). Prefrontal cortex HbO2 concentration measurements were taken during the duration of all PA conditions. Statistical Analysis Baseline fNIR recordings were taken for three minutes prior to the start of the PA conditions; the average HbO2 concentration over this time window was set as the baseline prefrontal HbO2 concentration. Raw prefrontal HbO2 concentrations for the standing and walking conditions were determined by comparing them to the baseline value; this was done by NIRSlab software. The HbO2 concentrations obtained throughout the duration of each condition were then averaged to determine the average prefrontal HbO2 concentration per condition. These values were then compared against one another. All fNIR recordings were pre-processed and analyzed using NIRSlab software. A band-pass filter was applied to prevent signals from unwanted frequencies from being included in the analyses; (i.e., noise and/or movement artifacts). The band-pass filter utilized a high-frequency cutoff of 0.70 Hz and a low-frequency cutoff of 0.002 Hz. Paired sample t-tests for all analyses were conducted in SPSS Version 25. Results Paired sample t-tests (n=21) were run to determine if there was a difference in RT (sec) and accuracy (# correct) on the standing and walking conditions. There was a significant decrease in RT during the walking conditions compared to the standing conditions; 0.59 s, SD = 0.05 vs.0 0.63 s, SD = 0.06 (p<.0001). There was a significant increase in accuracy in the walking conditions compared to the standing conditions; 38.90 ± 13.99 vs. 34.93 ± 16.67 (p<0.0001). Paired sample t-tests (n=4) were computed to determine if there was a difference in total prefrontal HbO2 concentration (□□mol) between the walking and standing conditions. No significant differences were found in total prefrontal HbO2 concentration between walking and standing conditions. Discussion The main finding of this study showed that RT and accuracy of standing conditions were significantly different from the walking conditions. With faster response times and increased accuracy observed in the walking condition, further study of the HbO2 concentration in the prefrontal region is warranted. Exercise intensity has a direct influence on cognitive performance (Hwang et al., 2017). The results confirm the possibility of an inverted U-shaped relationship between exercise and neurocognitive response, whereby, an improvement in cognitive performance could be expected from a moderate-intensity of exercise (Brisswalter, Collardeau, & René (2002). Correspondingly, if the exercise intensity is too high, there could be a decrease in cognitive performance. Petruzzello and his colleagues (1991) indicated that acute exercise lasting at least 20 minutes leads to a reduction in state and trait anxiety. However, when exercise duration lasts more than one hour, the appearance of fatigue symptoms were reported. Moreover, varied tasks such as cognitive engaging exercise, like the present study, also impacts cognitive performance (Jaeger, Schmidt, Conzelmann, & Roebers, 2014; Tomporowski, McCullick, Pendleton, & Pesce, 2015).