Cardiovascular Effects From Venous Blood Pooling in the Lower Limbs During Prolonged Sitting.

PURPOSE: To investigate whether venous blood pooling in the lower limbs from prolonged sitting induces harmful cardiovascular effects by reducing stroke volume (SV) and cardiac output (CO). METHODS: A randomized crossover trial involving 16 participants (mean age = 24.8 years ± 6.0 years, 44% women, 1 dropout) was conducted. The trial consisted of 2 conditions: cuff and noncuff, both involving 2 hours of prolonged sitting with tourniquets placed proximal to each knee. In the cuff condition, the tourniquets were inflated to subdiastolic pressure, allowing arterial inflow but preventing venous outflow. Venous blood pooling was assessed by measuring calf circumference. Cardiac Doppler sonography was used to measure CO, SV, and heart rate (HR) before and after the sitting period. RESULTS: Although the interaction effect between venous blood pooling and CO was not statistically significant (P = .190), there was a significant main effect for time (effect size [ES] = 0.36, ß = -0.238, 5.42% decrease). A medium-sized time-by-condition interaction effect for SV was observed (ES = 0.37, ß = 6.165), with a 5.87% decrease in the cuff condition and a 2.81% increase in the noncuff condition. Furthermore, there was a large interaction effect for venous blood pooling as measured by calf circumference (ES = 1.98, ß = -0.987), with a 3.69% increase in the cuff condition and a 0.03% increase in the noncuff condition. DISCUSSION: Understanding the physiological adaptations that occur during prolonged sitting can provide insight into how and how often to interrupt sitting to prevent deleterious cardiovascular effects. SV decreased during the sitting period of 120 minutes in the cuff condition and increased slightly during in the noncuff condition. However, the changes in CO and HR were more variable and were not perfectly in line with the authors' hypotheses. CONCLUSION: The findings indicate that as venous blood pooling increases during prolonged sitting, SV decreases, suggesting venous blood pooling influences certain hemodynamic changes associated with prolonged sitting.

Effects of intermittent exercise during prolonged sitting on executive function, cerebrovascular, and psychological response: a randomized crossover trial.

Emerging evidence indicates that acute bouts of uninterrupted prolonged sitting decrease cerebral blood flow and impair executive function. Few studies have investigated the use of feasible sedentary behavior interruptions to attenuate these effects. This study aimed to investigate the effects of intermittent half-squat exercises during prolonged sitting on executive function. Twenty participants (45% women, 21 ± 1 yr) were randomized to sit for 3 h 1) without any interruptions (control) or 2) with 1 min half-squats every 20 min (exercise). Executive function was determined using the Color Word Stroop Test (CWST) and Trail Making Test-B (TMT-B). Subjective feelings of arousal and measures of fatigue, concentration, and motivation were evaluated. Internal carotid artery (ICA) blood flow was measured using Doppler ultrasound. There was a significant interaction effect for correct response times with the incongruent CWST (P < 0.01), which were 3.5% faster in the exercise and 4.2% slower in the control over 3 h of sitting. There was also a significant interaction effect for TMT-B completion times (P < 0.01), which were 10.0% faster in the exercise and 8.8% slower in the control. Exercise suppressed decreases in concentration with a significant interaction effect (-28.7% vs. -9.2% for control vs. exercise, P = 0.048) and increases in mental fatigue with a significant interaction effect (285% vs. 157% for control vs. exercise, P < 0.04). These changes may have been related to changes in ICA blood flow, which had a significant interaction effect (P = 0.087). These results suggest that a simple strategy like intermittent squat exercises could help to maintain executive function during prolonged sitting.NEW & NOTEWORTHY We assessed executive function, cardiovascular, and cerebrovascular responses during 3-h prolonged sitting, with or without an exercise interruption (1 min squats every 20 min). Compared to uninterrupted sitting, exercise interruption suppressed sitting-induced reductions in cerebral blood flow and impairments in executive function. These results demonstrated the efficacy of a half-squat intervention for individuals seeking to preserve cognition during prolonged sitting, which may be useful in environments with limited resources such as the workplace.

The relationship between sleep duration and arterial stiffness: A meta-analysis.

Chronically short (<7 h) and long (>9 h) sleep duration may increase cardiovascular disease (CVD) risk relative to the recommended sleep duration (7-9 h). The objective of this study was to evaluate the effects of short and long sleep duration on arterial stiffness, a marker of CVD risk, in adults. Eleven cross-sectional studies were reviewed with a total sample size of 100,050 participants (64.5% male). Weighted mean differences (WMD) and 95% confidence intervals (95% CI) were calculated and pooled using random effects models, and standardized mean differences (SMD) were calculated to determine effect size magnitude. Compared to the recommended sleep duration, both short (WMD = 20.6 cm/s, 95% confidence intervals (CI): 13.8-27.4 cm/s, SMD = 0.02) and long sleep duration (WMD = 33.6 cm/s, 95% CI: 20.0-47.2 cm/s, SMD = 0.79) were associated with higher (detrimental) pulse wave velocity (PWV). The associations between short sleep and higher PWV in adults with cardiometabolic disease, and long sleep and higher PWV in older adults, were also significant in sub-group analysis. These findings indicate short and long sleep duration may contribute to subclinical CVD.

Sedentary behavior and cardiovascular disease risk: An evolutionary perspective.

A ubiquitous aspect of contemporary societies is sedentary behavior (SB), defined as low intensity activities in a seated, reclined, or supine posture. Leading public health agencies, including the World Health Organization, have recognized the strong association between SB and poor health outcomes, particularly cardiovascular disease. However, while public health agencies have begun to advocate for "reductions" in SB, the current US guidelines are typically vague and non-specific. There is good reasoning behind this non-committal advocacy-there is limited mechanistic and clinical evidence to support policy development. To guide SB policy development, it is important to first consider the origins and evolution of SB, including the following: 1) is SB really a novel/contemporary behavior? i.e., how has this behavior evolved? 2) how did our ancestors sit and in what contexts? 3) how does SB interact with 24-hour activity behaviors, including physical activity and sleep? 4) what other historical and contemporary facets of life interact with SB? and 5) in what context do these behaviors occur and how might they provide different evolutionarily novel stressors? This perspective article will synthesize the available evidence that addresses these questions and stimulate discussion pertaining to the lessons that we can learn from an historical and evolutionary perspective. Last, it will outline the gaps in current SB interruption literature that are hindering development of feasible SB reduction policy.

Protocol for a Longitudinal Study of the Determinants of Metabolic Syndrome Risk in Young Adults.

Context: As many as 76.7% of U.S. young adults have at least one metabolic syndrome risk factor. Often undetected, metabolic syndrome risk factors cluster with other risk factors increasing risk of future cardiometabolic disease. The prevention of metabolic syndrome risk accrual through early behavioral interventions is crucial for at-risk populations. Objectives: This paper outlines the protocol for the Health E Start study, including the objectives, methodology, ethics, and dissemination. Additionally, we discuss the goals of the National Institutes of Health Research Enhancement Award (R15) that funded this project and how this funding will facilitate the comprehensive training of undergraduate researchers. The long-term goal of the study is to develop a theoretically driven intervention for the prevention of metabolic syndrome risk development in college students. To facilitate this goal, the aims are to identify 1) behavioral targets for the prevention of metabolic syndrome risk development and 2) the motivations behind such behaviors to develop a theoretical framework for use in intervention design. Design: Longitudinal observational design. Setting: Transition from living at home to independent living at colleges across the U.S. Participants: High school seniors (n = 150) who will be transitioning to college within 3 months of graduating. Main Outcome Measure: For aim 1, metabolic syndrome risk will be quantified into a risk score using a principal components analysis of traditional risk factors. Associations between changes in lifestyle behaviors and changes in the risk score will identify population-specific behavioral targets. For aim 2, changes in psychological, social, and environmental antecedents of observed behaviors will be identified. Conclusions: Identifying the relationship between behavior change and metabolic syndrome risk, and the psychosocial and environmental predictors of observed behavior changes will facilitate the design of targeted interventions for the prevention of metabolic syndrome risk progression in the early college years.