Group III/IV Afferent Activation During Prolonged Sitting With Mild-Hypercapnia In Middle-Aged Adults: A Pilot Study

Abstract

Prolonged sitting (PS) and sedentarism in the US has significantly increased in recent decades, leading many adults to spend a majority of their workday sedentary. Uninterrupted PS has been shown to cause endothelial dysfunction in the lower limbs, leading to an increased risk for cardiovascular disease such as peripheral arterial disease. Additionally, elevations in carbon dioxide (hypercapnia), commonly observed in crowded environments such as workplaces and/or classrooms, have been known to impair cardiovascular function. Interruptions to PS by muscular contraction can prevent the negative effects attributed to PS. However, the underlying mechanisms of these muscle contractions in the prevention of the negative effects of PS within a hypercapnic condition in middle-aged adults, is currently unknown. PURPOSE: Examine the impacts of muscle contraction, specifically, group III/IV muscle afferent activation via passive and active leg movement in middle aged adults during prolonged sitting in a mild hypercapnic environment. METHODS: Healthy sedentary middle-aged adults (n =4, 48± 7 years old) participated. Utilizing a randomized control design participants completed 2 visits: control (CON) and active (group III/IV muscle afferent activation, ACT). Each visit included 2.5 hours of PS in a mild-hypercapnic environment to determine how activation of group III (mechanosensitive reflex) and/or group IV (metabosensitive reflex) afferents affect cardiovascular function respectively. RESULTS: Responses to ACT between 0-min and 250-min showed a 12% increase in blood flow (BF) and a 27.74% increase in shear rate (SR), while CON showed a 0.23% decrease in BF and an 8.9% increase in SR. Flow mediated dilation (FMD) of the popliteal artery increased following ACT (2.45 ± 0.82%) and decreased in CON (-1.45 ± 1.21%) while brachial artery FMD found increases in both conditions (ACT: 4.075 ± 0.92%, CON: 0.76 ± 0.54%). CONCLUSION: The findings from this study provide a novel insight towards the cardiovascular effects of PS within mild hypercapnia in sedentary middle-aged adults and the role of group III and IV muscle afferent activation for the mechanism(s) behind the preservation of vascular function via muscular contraction. Supported by the University of Nebraska at Omaha Graduate Research and Creative Activity grant.