Hemodynamic responses during prolonged sitting

Sitting leg vasculopathy: potential adaptations beyond the endothelium

Increased sitting time, the most common form of sedentary behavior, is an independent risk factor for all-cause and cardiovascular disease mortality; however, the mechanisms linking sitting to cardiovascular risk remain largely elusive. Studies over the last decade have led to the concept that excessive time spent in the sitting position and the ensuing reduction in leg blood flow-induced shear stress cause endothelial dysfunction. This conclusion has been mainly supported by studies using flow-mediated dilation in the lower extremities as the measured outcome. In this review, we summarize evidence from classic studies and more recent ones that collectively support the notion that prolonged sitting-induced leg vascular dysfunction is likely also attributable to changes occurring in vascular smooth muscle cells (VSMCs). Indeed, we provide evidence that prolonged constriction of resistance arteries can lead to modifications in the structural characteristics of the vascular wall, including polymerization of actin filaments in VSMCs and inward remodeling, and that these changes manifest in a time frame that is consistent with the vascular changes observed with prolonged sitting. We expect this review will stimulate future studies with a focus on VSMC cytoskeletal remodeling as a potential target to prevent the detrimental vascular ramifications of too much sitting.

The Effect of Sitting Duration on Peripheral Blood Pressure Responses to Prolonged Sitting, With and Without Interruption: A Systematic Review and Meta-Analysis

BACKGROUND

A previous meta-analysis reported that: (i) an acute bout of prolonged uninterrupted sitting induces a significant increase in peripheral blood pressure (BP) and (ii) the increase in BP can be offset by interrupting the sitting bout with light aerobic activities such as walking. However, the temporal association between prolonged uninterrupted sitting and BP was not determined. A better understanding of temporality, for example, how long it takes BP to increase, will assist in prescribing sitting interruption strategies.

OBJECTIVES

We aimed to determine: (1) the temporal association between the duration of uninterrupted sitting and BP and (2) whether regular sitting interruptions moderate the association between uninterrupted sitting and BP.

DATA SOURCES

Electronic databases (PubMed, Web of Science, SPORTDiscus) were searched from inception to July 2022. Reference lists of eligible studies and relevant reviews were also screened.

STUDY SELECTION

Inclusion criteria for objective (1) were: (i) participants aged ≥ 18 years; (ii) a prolonged sitting bout ≥ 1 h; and (iii) peripheral BP measurements (systolic BP, diastolic BP, and/or mean arterial pressure) at more than two timepoints during the sitting bout. Additional criteria for objective (2) were: (i) the sitting interruption strategy was implemented during the sitting bout (i.e., not prior to engaging in sitting) and (ii) the study included a control (uninterrupted sitting) condition or group.

APPRAISAL AND SYNTHESIS METHODS

There were 1555 articles identified, of which 33 met inclusion criteria for objective (1). Of those articles, 20 met inclusion criteria for objective (2). To investigate the effect of sitting duration on the BP response, unstandardized b coefficients (mmHg/h) and 95% confidence intervals (CIs) were calculated using a three-level mixed-effect meta-regression.

RESULTS

Increased sitting duration was positively associated with systolic BP (b = 0.42 mmHg/h, 95% CI 0.18-0.60), diastolic BP (b = 0.24 mmHg/h, 95% CI 0.06-0.42), and mean arterial pressure (b = 0.66 mmHg/h, 95% CI 0.36-0.90). In trials where sitting was interrupted, there was a significant decrease in systolic BP (b = - 0.24 mmHg/h, 95% CI - 0.42 to - 0.06) and diastolic BP (b = - 0.24 mmHg/h, 95% CI - 0.42 to - 0.12), and a non-significant change in mean arterial pressure (p = 0.69).

CONCLUSIONS

Increased uninterrupted sitting duration results in greater increases in BP; however, regularly interrupting sitting may offset negative effects.

The 24-h activity cycle and cardiovascular outcomes: establishing biological plausibility using arterial stiffness as an intermediate outcome

This review proposes a biologically plausible working model for the relationship between the 24-h activity cycle (24-HAC) and cardiovascular disease. The 24-HAC encompasses moderate-to-vigorous physical activity (MVPA), light physical activity, sedentary behavior (SB), and sleep. MVPA confers the greatest relative cardioprotective effect, when considering MVPA represents just 2% of the day if physical activity guidelines (30 min/day) are met. While we have well-established guidelines for MVPA, those for the remaining activity behaviors are vague. The vague guidelines are attributable to our limited mechanistic understanding of the independent and additive effects of these behaviors on the cardiovascular system. Our proposed biological model places arterial stiffness, a measure of vascular aging, as the key intermediate outcome. Starting with prolonged exposure to SB or static standing, we propose that the reported transient increases in arterial stiffness are driven by a cascade of negative hemodynamic effects following venous pooling. The subsequent autonomic, metabolic, and hormonal changes further impair vascular function. Vascular dysfunction can be offset by using mechanistic-informed interruption strategies and by engaging in protective behaviors throughout the day. Physical activity, especially MVPA, can confer protection by chronically improving endothelial function and associated protective mechanisms. Conversely, poor sleep, especially in duration and quality, negatively affects hormonal, metabolic, autonomic, and hemodynamic variables that can confound the physiological responses to next-day activity behaviors. Our hope is that the proposed biologically plausible working model will assist in furthering our understanding of the effects of these complex, interrelated activity behaviors on the cardiovascular system.

Physiology of sedentary behavior

Sedentary behaviors (SB) are characterized by low energy expenditure while in a sitting or reclining posture. Evidence relevant to understanding the physiology of SB can be derived from studies employing several experimental models: bed rest, immobilization, reduced step count, and reducing/interrupting prolonged SB. We examine the relevant physiological evidence relating to body weight and energy balance, intermediary metabolism, cardiovascular and respiratory systems, the musculoskeletal system, the central nervous system, and immunity and inflammatory responses. Excessive and prolonged SB can lead to insulin resistance, vascular dysfunction, shift in substrate use toward carbohydrate oxidation, shift in muscle fiber from oxidative to glycolytic type, reduced cardiorespiratory fitness, loss of muscle mass and strength and bone mass, and increased total body fat mass and visceral fat depot, blood lipid concentrations, and inflammation. Despite marked differences across individual studies, longer term interventions aimed at reducing/interrupting SB have resulted in small, albeit marginally clinically meaningful, benefits on body weight, waist circumference, percent body fat, fasting glucose, insulin, HbA1c and HDL concentrations, systolic blood pressure, and vascular function in adults and older adults. There is more limited evidence for other health-related outcomes and physiological systems and for children and adolescents. Future research should focus on the investigation of molecular and cellular mechanisms underpinning adaptations to increasing and reducing/interrupting SB and the necessary changes in SB and physical activity to impact physiological systems and overall health in diverse population groups.

Prolonged sitting and peripheral vascular function: potential mechanisms and methodological considerations

Sitting time is associated with increased risks for subclinical atherosclerosis and cardiovascular disease development, and this is thought to be partially due to sitting-induced disturbances in macro- and microvascular function as well as molecular imbalances. Despite surmounting evidence supporting these claims, contributing mechanisms to these phenomena remain largely unknown. In this review, we discuss evidence for potential mechanisms of sitting-induced perturbations in peripheral hemodynamics and vascular function and how these potential mechanisms may be targeted using active and passive muscular contraction methods. Furthermore, we also highlight concerns regarding the experimental environment and population considerations for future studies. Optimizing prolonged sitting investigations may allow us to not only better understand the hypothesized sitting-induced transient proatherogenic environment but to also enhance methods and devise mechanistic targets to salvage sitting-induced attenuations in vascular function, which may ultimately play a role in averting atherosclerosis and cardiovascular disease development.

Aortic stiffness increases during prolonged sitting independent of intermittent standing or prior exercise

INTRODUCTION

Adverse vascular responses can occur during prolonged sitting, including stiffening of the aortic artery which may contribute to cardiovascular disease. Few studies have investigated the impact of intermittent standing and/or prior exercise as strategies to attenuate these potentially deleterious vascular changes.

PURPOSE

To investigate central vascular health responses during prolonged sitting, with and without intermittent standing and/or prior exercise.

METHODS

Fifteen males aged 18 to 31 years were recruited. Subjects completed a control condition [Sitting Only (SO)], and three randomized strategy conditions [Sitting Plus Standing (SSt), Exercise Plus Sitting (ES), Exercise Plus Sitting Plus Standing (ESSt)]. For all conditions, measurements of carotid-femoral pulse wave velocity (cfPWV) were taken at pre- and post-intervention, and brachial and central blood pressure (BP) at pre-, 1-h, 2-h, and 3-h intervention.

RESULTS

cfPWV significantly increased from pre- to post-intervention for all conditions (all p ≤ 0.043), as did brachial mean arterial pressure (MAP) and diastolic BP, and central MAP and diastolic BP for the control condition (all p ≤ 0.022). Brachial and central systolic BP were significantly higher during SO compared to ESSt at 1 h, and compared to ES for central systolic BP (all p ≤ 0.036).

CONCLUSIONS

Strategies of intermittent standing and/or prior exercise may not prevent aortic stiffening during sitting but may attenuate BP elevations in the brachial and aortic arteries. Future research should investigate causal mechanistic links between sitting and aortic stiffening, and other attenuation strategies.

Evaluating the biomechanics of an in-between posture to create a multi-posture office environment

BACKGROUND

Prolonged sitting during work is common and has been shown to cause health issues. However, changing working postures has been reported to reduce musculoskeletal issues and impact other health issues; thus, there is a need for an office environment with multiple choices of working postures.

OBJECTIVE

The purpose of this study was to evaluate changes in body position, body loading, and blood perfusion while in a seated, standing, and new office seating position, termed the in-between position.

METHODS

Ground reaction forces, joint angles, pelvic tilt, openness angle (angle between the pelvis plane and thorax), and blood perfusion were evaluated for three positions. A motion capture system with markers was used to capture the position of anatomical landmarks. A six-axis force plate was used to collect the ground reaction forces, and a laser doppler perfusion monitor was used to obtain the blood perfusion.

RESULTS

Data showed that the in-between position articulated the hips, which provided a hip and lumbar position closer to a standing posture than a seated posture. The average vertical ground reaction force in the in-between position was larger than the seated position but significantly smaller than during standing (p < 0.0001). There were no significant differences in anterior/posterior ground reaction forces between the seated and the in-between positions (p = 0.4934). Lastly, blood perfusion increased during the dynamic transitions between positions indicating changes in blood flow.

CONCLUSION

The in-between position provides benefits of both standing (larger pelvic tilt and increased lumbar lordosis) and sitting (reduction in ground reaction forces).

Effects of passive and active leg movements to interrupt sitting in mild hypercapnia on cardiovascular function in healthy adults

Prolonged sitting in a mild hypercapnic environment impairs peripheral vascular function. The effects of sitting interruptions using passive or active skeletal muscle contractions are still unclear. Therefore, we sought to examine the vascular effects of brief periods (2 min every half hour) of passive and active lower limb movement to interrupt prolonged sitting with mild hypercapnia in adults. Fourteen healthy adults (24 ± 2 yr) participated in three experimental visits sitting for 2.5 h in a mild hypercapnic environment (CO₂ = 1,500 ppm): control (CON, no limb movement), passive lower limb movement (PASS), and active lower limb movement (ACT) during sitting. At all visits, brachial and popliteal artery flow-mediated dilation (FMD), microvascular function, plasmatic levels of nitrate/nitrite and endothelin-1, and heart rate variability were assessed before and after sitting. Brachial and popliteal artery FMDs were reduced in CON and PASS (P < 0.05) but were preserved (P > 0.05) in ACT. Microvascular function was blunted in CON (P < 0.05) but was preserved in PASS and ACT (P > 0.05). In addition, total plasma nitrate/nitrite was preserved in ACT (P > 0.05) but was reduced in CON and PASS (P < 0.05), and endothelin-1 levels were decreased in ACT (P < 0.05). Both passive and active movement induced a greater ratio between the low-frequency and high-frequency bands for heart rate variability (P < 0.05). For the first time, to our knowledge, we found that brief periods of passive leg movement can preserve microvascular function, but that an intervention that elicits larger increases in shear rate, such as low-intensity exercise, is required to fully protect both macrovascular and microvascular function and circulating vasoactive substance balance.NEW & NOTEWORTHY Passive leg movement could not preserve macrovascular endothelial function, whereas active leg movement could protect endothelial function. Attenuated microvascular function can be salvaged by passive movement and active movement. Preservation of macrovascular hemodynamics and plasma total nitrate/nitrite and endothelin-1 during prolonged sitting requires active movement. These findings dissociate the impacts induced by mechanical stress (passive movement) from the change in metabolism (active movement) on the vasculature during prolonged sitting in a mild hypercapnic environment.

Effect of Electrical Muscle Stimulation on Vascular Endothelial Function during Prolonged Sitting

OBJECTIVE

While prolonged sedentary behaviors (SBs) increase cardiovascular disease (CVD) risk, interrupting prolonged sitting (PS) with frequent light exercise reduces arterial functional decline. Skeletal muscle electrical stimulation (EMS) enhances peripheral circulation through passive muscle contraction, suggesting that EMS reduces CVD risk by providing an alternative to active exercise for prolonged SBs. This study aimed to investigate the effects of EMS to skeletal muscles during PS on the endothelial function of the brachial artery (BA).

METHODS

Study participants included 12 healthy adult men who were subjected to 15 min of supine rest, followed by 1 h of PS only (control [CON] trial), or 20 min of EMS to the lower extremities at 50% of the maximum tolerance intensity during PS (EMS trial). Flow-mediated dilation (FMD) of the BA was measured before and 30 min after PS, and normalized FMD (nFMD) was calculated.

RESULTS

The nFMD of the CON trial significantly decreased 30 min after PS completion (6.21% ± 1.13%) compared with that before PS (7.26% ± 0.73%), and there was no significant change in the EMS trial before and after PS. The EMS trial showed a significant increase in the nFMD 30 min after PS completion (1.14 ± 0.77) compared with that before PS (0.84 ± 0.43). However, no significant difference was observed in the CON trials.

CONCLUSION

Passive contraction of the lower extremity muscles by EMS increases BA nFMD, suggesting that prolonged sedentary lower extremity EMS use may reduce the risk of vascular endothelial dysfunction.

Co-Production at Work: The Process of Breaking Up Sitting Time to Improve Cardiovascular Health. A Pilot Study

Prolonged sitting negatively affects several cardiovascular disease biomarkers. Current workplace physical activity interventions to reduce sitting result in inconsistent uptake and adherence rates. Co-production attempts to improve the translation of evidence to practice through engaging the participants within the intervention design, improving the context sensitivity and acceptability of the intervention. A needs analysis questionnaire was initially conducted (n = 157) to scope workplace behaviours and attitudes. A development group (n = 11) was consulted in focus groups around the needs analysis findings and asked to comment on the feasibility of a proposed intervention. A pilot intervention was then carried out (n = 5). The needs analysis indicated that only 1.8% (n = 4) engaged in occupational physical activity, and 68.7% (n = 103) sat for ≥6 h during their working day. Through the focus groups, an intervention breaking up sitting time hourly with five-minute walking breaks was co-produced. Cultural and pragmatic issues concerning the implementation of frequent physical activity breaks from sitting and the subsequent impact on work productivity were highlighted. The pilot intervention increased the number of breaks from sedentary behaviour from 2 to 11. The co-production methodology resulted in a research- and stakeholder-guided compromise. Large-scale intervention implementation is required before firm effectiveness conclusions can be made.

The Effects of Acute Exposure to Prolonged Sitting, with and Without Interruption, on Peripheral Blood Pressure Among Adults: A Systematic Review and Meta-Analysis

BACKGROUND

Previous reviews have shown that exposure to acute prolonged sitting can have detrimental effects on several cardiovascular and cardiometabolic health markers. However, to date, there has been no synthesis of peripheral blood pressure data (including systolic blood pressure, diastolic blood pressure and mean arterial pressure), an important and translatable marker of cardiovascular health. Similarly, no previous study has consolidated the effects of sitting interruptions on peripheral blood pressure.

OBJECTIVES

We aimed to (1) assess the effect of exposure to acute prolonged sitting on peripheral blood pressure and (2) determine the efficacy of sitting interruption strategies as a means of offsetting any negative effects. Subgroup analyses by age and interruption modality were performed to explore heterogeneity.

DATA SOURCES

Electronic databases (PubMed, Web of Science and, SPORTDiscus) were searched from inception to March 2021. Reference lists of eligible studies and relevant reviews were also screened.

STUDY SELECTION

Inclusion criteria for objective (1) were: (i) peripheral blood pressure was assessed non-invasively in the upper limb pre-sitting and post-sitting; (ii) studies were either randomised controlled, randomised crossover or quasi-experimental pre-test vs post-test trials; (iii) the sitting period was ≥ 1 h; (iv) pre-sitting and post-sitting measures were performed in the same posture; and (v) participants were adults (aged ≥ 18 years), free of autonomic or neuromuscular dysfunction. Additional criteria for objective (2) were: (i) the interruption strategy was during the sitting period; (ii) there was an uninterrupted sitting control condition; and (iii) the interruption strategy must have involved participants actively moving their upper or lower limbs.

APPRAISAL AND SYNTHESIS METHODS

In total, 9763 articles were identified, of which 33 met inclusion criteria for objective (1). Of those articles, 22 met inclusion criteria for objective (2). Weighted mean difference (WMD), 95% confidence intervals (95% CI), and standardised mean difference (SMD) were calculated for all trials using inverse variance heterogeneity meta-analysis modelling. Standardised mean difference was used to determine the magnitude of effect, where < 0.2, 0.2, 0.5 and 0.8 were defined as trivial, small, moderate and large, respectively.

RESULTS

(1) Prolonged uninterrupted sitting resulted in trivial and small significant increases in systolic blood pressure (WMD = 3.2 mmHg, 95% CI 0.6 to 5.8, SMD = 0.14) and mean arterial pressure (WMD = 3.3 mmHg, 95% CI 2.2 to 4.4, SMD = 0.37), respectively, and a non-significant trivial increase in diastolic blood pressure. Subgroup analyses indicated that the increases in systolic blood pressure and mean arterial pressure were more pronounced in younger age groups. (2) Interrupting bouts of prolonged sitting resulted in significantly lower systolic blood pressure (WMD =  - 4.4 mmHg, 95% CI - 7.4 to - 1.5, SMD = 0.26) and diastolic blood pressure (WMD =  - 2.4 mmHg, 95% CI - 4.5 to - 0.3, SMD = 0.19) compared with control conditions, particularly when using aerobic interruption strategies.

CONCLUSIONS

Exposure to acute prolonged uninterrupted sitting results in significant increases in systolic blood pressure and mean arterial pressure, particularly in younger age groups. Regularly interrupting bouts of prolonged sitting, particularly with aerobic interruption strategies may reduce negative effects.

The Influence of Sedentary Behavior on the Relationship Between Cognitive Function and Vascular Function in Older Adults with and without Chronic Kidney Disease

Cognitive impairment and vascular dysfunction are common in older adults with and without chronic kidney disease (CKD). Older adults with and without CKD are also sedentary - a behavior associated with cognitive and vascular function. The objective of this study was to explore whether sedentary behavior influenced the relationship between cognitive and vascular function in older adults with preclinical cognitive impairment with and without CKD. In our study, 48 older adults underwent assessment of cognition, vascular compliance, and sedentary behavior, and relationships were explored with regression moderation analysis. Sedentary time and breaks did not moderate the relationship between vascular and cognitive function. Although significant moderation was not found, cognition, vascular function, and sedentary behavior are important to assess when evaluating older adults with and without CKD.

A Primer on Repeated Sitting Exposure and the Cardiovascular System: Considerations for Study Design, Analysis, Interpretation, and Translation

Sedentary behavior, particularly sitting, is ubiquitous in many contemporary societies. This is a major societal concern considering the evidence for a strong association between sitting behavior and cardiovascular disease morbidity and mortality. Unsurprisingly, leading public health agencies have begun to advocate “reduction” in sitting behavior. Though, the guidelines are typically vague and non-specific. The lack of specific guidelines for prolonged sitting is attributable to the absence of available evidence to facilitate guideline development. To inform policy, well-designed randomized controlled trials are required to test the efficacy of specific and translatable sitting reduction strategies. To guide the design of randomized controlled trials, this review postulates that several gaps in the literature first need to be filled. Following a general discussion of the importance of sitting behavior to contemporary societies, each of the following are discussed: (i) acute sitting exposure and systems physiology; (ii) recommendations for a systems physiology toolbox; (iii) study design considerations for acute sitting exposure; and (iv) translation of sitting-focused research.

Associations of Sedentary Time with Heart Rate and Heart Rate Variability in Adults: A Systematic Review and Meta-Analysis of Observational Studies

PURPOSE

To evaluate if sedentary time (ST) is associated with heart rate (HR) and variability (HRV) in adults.

METHODS

We systematically searched PubMed and Google Scholar through June 2020. Inclusion criteria were observational design, humans, adults, English language, ST as the exposure, resting HR/HRV as the outcome, and (meta-analysis only) availability of the quantitative association with variability. After qualitative synthesis, meta-analysis used inverse variance heterogeneity models to estimate pooled associations.

RESULTS

Thirteen and eight articles met the criteria for the systematic review and meta-analysis, respectively. All studies were cross-sectional and few used gold standard ST or HRV assessment methodology. The qualitative synthesis suggested no associations between ST and HR/HRV. The meta-analysis found a significant association between ST and HR (β = 0.24 bpm per hour ST; CI: 0.10, 0.37) that was stronger in males (β = 0.36 bpm per hour ST; CI: 0.19, 0.53). Pooled associations between ST and HRV indices were non-significant (p > 0.05). Substantial heterogeneity was detected.

CONCLUSIONS

The limited available evidence suggests an unfavorable but not clinically meaningful association between ST and HR, but no association with HRV. Future longitudinal studies assessing ST with thigh-based monitoring and HRV with electrocardiogram are needed.

Effect of Reducing Sedentary Behavior on Blood Pressure (RESET BP): Rationale, design, and methods

Sedentary behavior (SB) has recently been recognized as a strong risk factor for cardiovascular disease, with new guidelines encouraging adults to 'sit less, move more.' Yet, there are few randomized trials demonstrating that reducing SB improves cardiovascular health. The Effect of Reducing Sedentary Behavior on Blood Pressure (RESET BP) randomized clinical trial addresses this gap by testing the effect of a 3-month SB reduction intervention on resting systolic BP. Secondary outcomes include other BP measures, pulse wave velocity, plasma renin activity and aldosterone, and objectively-measured SB (via thigh-mounted activPAL) and physical activity (via waist-worn GT3X accelerometer). RESET BP has a targeted recruitment of 300 adults with desk jobs, along with elevated, non-medicated BP (systolic BP 120-159 mmHg or diastolic BP 80-99 mmHg) and physical inactivity (self-reported aerobic physical activity below recommended levels). The multi-component intervention promotes 2-4 fewer hours of SB per day by replacing sitting with standing and light-intensity movement breaks. Participants assigned to the intervention condition receive a sit-stand desk attachment, a wrist-worn activity prompter, behavioral counseling every two weeks (alternating in-person and phone), and twice-weekly automated text messages. Herein, we review the study rationale, describe and evaluate recruitment strategies based on enrollment to date, and detail the intervention and assessment protocols. We also document our mid-trial adaptations to participant recruitment, intervention deployment, and outcome assessments due to the intervening COVID-19 pandemic. Our research methods, experiences to date, and COVID-specific accommodations could inform other research studying BP and hypertension or targeting working populations, including those seeking remote methods.

Arterial stiffness responses to prolonged sitting combined with a high-glycemic-index meal: a double-blind, randomized crossover trial

Regular exposure to uninterrupted prolonged sitting and the consumption of high-glycemic-index (HGI) meals is independently associated with increased cardiovascular disease risk. Sitting for as little as 1 h can impair the health of both peripheral and central arteries. However, it is currently unknown whether combined acute exposure to uninterrupted prolonged sitting and an HGI meal is more detrimental to global (peripheral and central) vascular health. The purpose of this study was to investigate the effect of prolonged sitting (3 h), following the consumption of an HGI or a low-glycemic-index (LGI) meal, on global pulse wave velocity (G-PWV). Eighteen healthy participants [70% female, mean (standard deviation, SD) age = 22.6 (3.1) yr, body mass index (BMI) = 25.5 (6.1) kg/m²] sat for 3 h after consuming an HGI or LGI meal. G-PWV was assessed by incorporating three PWV measures (carotid-femoral, brachial-femoral, and femoral-ankle). The effects of time (PRE vs. POST) and condition (LGI vs. HGI) were analyzed using linear mixed models. Following prolonged sitting, G-PWV increased by 0.29 m/s (i.e., PRE vs. POST). However, the condition (P = 0.987) and time × condition (P = 0.954) effects were nonsignificant. The current findings support previous research showing an increase in arterial stiffness with prolonged sitting. However, in young and healthy adults, the arterial stiffness response was not worsened through HGI meal consumption.NEW & NOTEWORTHY We used novel statistical techniques and study design characteristics to examine how the cardiovascular disruptions due to prolonged sitting are changed after the consumption of low- and high-glycemic-index meals. The current study indicates that changes in arterial stiffness due to prolonged sitting are not worsened in young, healthy adults after the consumption of a high-glycemic-index meal.

Effects of Acute Prolonged Sitting and Interrupting Prolonged Sitting on Heart Rate Variability and Heart Rate in Adults: A Meta-Analysis

Prolonged sitting increases cardiovascular disease (CVD) risk, however the physiological mechanisms contributing to CVD from acute sitting exposure are not well-understood. Therefore, this study investigated the heart rate (HR) and variability (HRV) responses to prolonged sitting and after interrupting prolonged sitting (e.g., walking). Electronic databases were searched (inception-August 2020) for studies which exposed adults to prolonged (≥1 h) sitting with and/or without interruptions. Twenty-one articles (27 trials, n = 537) met inclusion criteria. Prolonged sitting non-significantly increased HR (weighted mean difference (WMD) = 0 bpm, 95% CI: −2, 3) and HRV (standardized mean difference (SMD) = 0.12, 95% CI: −0.08, 0.33) compared to pre-sitting baseline. Interrupting prolonged sitting yielded a non-significant small increase in HR (WMD = 4 bpm, 95% CI: 0, 7) compared to pre-sitting baseline. Sub-group analyses investigating interrupting prolonged sitting revealed small-to-moderate increases in HR in healthy populations (WMD = 6 bpm, 95% CI: 1, 10) and following walking interruptions (WMD = 7 bpm, 95% CI: 3, 11). In conclusion, prolonged sitting does not significantly affect HR or HRV. However, interrupting prolonged sitting yielded a small non-significant increase in HR, potentially indicative of increased metabolic demand. Further research is needed to investigate poor CVD outcomes via autonomic disruption from prolonged sitting.

Examining sex differences in sitting-induced microvascular dysfunction: Insight from acute vitamin C supplementation

PURPOSE

Lower limb microvascular dysfunction resulting from prolonged sitting (PS) bouts has been revealed to occur independent of sex. Although acute antioxidant supplementation has been reported to blunt conduit artery dysfunction following PS in young males, it is unknown if this protective effect extends to the microvasculature or is relevant in young females, who possess intrinsic vascular protective mechanisms specific to antioxidant defense. Therefore, this study employed an acute antioxidant supplementation to further examine sex differences during PS with a specific focus on microvascular function.

METHODS

On two separate visits, 14 females (23 ± 3 years) and 12 males (25 ± 4 years) had leg microvascular function (LMVF) assessed (via the passive leg movement technique) before and after 1.5 h of sitting. Prior to each visit, one gram of vitamin C (VC) or placebo (PL) was consumed.

RESULTS

PS significantly reduced LMVF [PL: (M: -34 ± 20; F: -23 ± 18%; p < 0.01) independent of sex (p = 0.7)], but the VC condition only blunted this reduction in males (VC: -3 ± 20%; p < 0.01), but not females (VC: -18 ± 25%; p = 0.5).

CONCLUSION

Young males and females reported similar reductions LMVF following PS, but only the young males reported a preservation of LMVF following the VC supplementation. This finding in young females was highlighted by substantial variability in LMVF measures in response to the VC condition that was unrelated to changes in the potential contributors to sitting-induced reductions in LMVF (e.g. lower limb venous pooling, reduced arterial shear rate).

NEW AND NOTEWORTHY

In this study, we employed an acute Vitamin C (VC) supplementation to examine sex differences in leg microvascular function (LMVF) following a bout of prolonged sitting. This study revealed that prolonged sitting reduced LMVF independent of sex, but only young males reported an attenuation to this lowered LMVF following VC supplementation. The young females revealed substantial variability in sitting-induced changes to LMVF that could not be explained by the potential contributors to sitting-induced reductions in LMVF (e.g. lower limb venous pooling, reduced arterial shear rate).

The Effects of a Simulated Workday of Prolonged Sitting on Seated versus Supine Blood Pressure and Pulse Wave Velocity in Adults with Overweight/Obesity and Elevated Blood Pressure

We evaluated the effects of a simulated workday of prolonged sitting on blood pressure (BP) and pulse wave velocity (PWV) and examined whether posture (seated vs. supine) affected responses. Participants (n = 25) were adults, with overweight/obesity and elevated BP, and performed seated desk work for 7.5 h. BP and PWV were measured in seated and supine postures at baseline (7:15 a.m.), midday (12:05 p.m.), and afternoon (4:45 p.m.). Generalized linear mixed models evaluated the effects of prolonged sitting on BP and PWV within each posture and interactions by posture and sex. In the recommended postures, seated BP and supine carotid-femoral pulse wave velocity (cfPWV) and carotid-ankle pulse wave velocity (caPWV), but not carotid-radial pulse wave velocity (crPWV), significantly increased over the simulated seated workday (all p < 0.05; effect sizes [d] ranged from 0.25 to 0.44). Whilst no posture-by-time interactions were observed (p > 0.05), BP, caPWV, and crPWV were higher when seated versus supine (main effects of posture p < 0.05; d ranged from 0.30 to 1.04). Exploratory analysis revealed that females had greater seated BP responses (p for interaction <0.05); seated PWV and supine BP and PWV responses were similar by sex (p for interaction >0.05). A simulated workday of prolonged sitting increased seated BP and supine cfPWV and caPWV, and posture minimally influenced these responses. These results add to the evidence suggesting a deleterious effect of prolonged sitting on cardiovascular health.

Impacts of prolonged sitting with mild hypercapnia on vascular and autonomic function in healthy recreationally active adults

Prolonged sitting, which is known to impair peripheral vascular function, often occurs in spaces (e.g., offices) with mild hypercapnic atmospheres. However, the effects of prolonged sitting in hypercapnic conditions on vascular function are unknown. Therefore, the purpose of this study was to investigate the effects of prolonged sitting in mild hypercapnic conditions on vascular and autonomic function in humans. Twelve healthy young adults participated in two experimental visits that consisted of sitting for 2.5 h in a control condition [normal atmospheric conditions sitting (PSIT)] or a mild hypercapnic condition (HCAP; CO₂ = 1,500 ppm). During each visit, heart rate variability (HRV), blood pressure (BP), pulse wave velocity (PWV), augmentation index (AIx), brachial and popliteal artery flow-mediated dilation (FMD), and near-infrared spectroscopy (NIRS) were assessed before and after prolonged sitting. Sitting significantly decreased AIx in both groups (P < 0.05). Brachial and popliteal FMD were reduced with sitting (P < 0.05), and the reduction in popliteal FMD was amplified by HCAP (P < 0.05). Baseline microvascular oxygenation was decreased following sitting in both groups (P < 0.05). However, microvascular reoxygenation upon cuff release was slower only in HCAP (P < 0.05). HRV, HR, BP, and PWV did not significantly change with sitting in either group (P > 0.05). We conclude that prolonged sitting attenuated both brachial and popliteal endothelial function and was associated with perturbed microcirculation. Additionally, mild hypercapnic conditions further impaired peripheral endothelial and microvascular function. Together, these findings suggest that prolonged sitting is accompanied by a host of deleterious effects on the vasculature, which are exacerbated by mild hypercapnia.NEW & NOTEWORTHY The results of this study reveal that prolonged sitting attenuates endothelial function and microvascular function. Additionally, prolonged sitting with mild hypercapnia, which is similar to everyday environments, further exacerbates peripheral endothelial function and microvascular function.

The short-term effects of sedentary behaviour on cerebral hemodynamics and cognitive performance in older adults: a cross-over design on the potential impact of mental and/or physical activity

BACKGROUND

Sedentary behaviour might be a potential risk factor for cognitive decline. However, the short-term effects of sedentary behaviour on (cerebro) vascular and cognitive performance in older people are unknown.

METHODS

We used a cross-over design with 22 older adults (78 years, 9 females) to assess the short-term hemodynamic and cognitive effects of three hours uninterrupted sitting and explored if these effects can be counteracted with regular (every 30 min) two-minute walking breaks. In addition, we investigated if low versus high mental activity during the three hours of sitting modified these effects. Before and after each condition, alertness, executive functioning, and working memory were assessed with the Test of Attentional Performance battery. Additionally, cerebral blood flow velocity (Transcranial Doppler) and blood pressure (Finapres) were measured in rest, and during sit-to-stand and CO₂ challenges to assess baroreflex sensitivity, cerebral autoregulation, and cerebral vasomotor reactivity.

RESULTS

No short-term differences were observed in cognitive performance, cerebral blood flow velocity, baroreflex sensitivity, cerebral autoregulation, or cerebral vasomotor reactivity across time, or between conditions. Blood pressure and cerebrovascular resistance increased over time (8.6 mmHg (5.0;12.1), p < 0.001), and 0.23 in resistance (0.01;0.45), p = 0.04). However, these effects were not mitigated by mental activity or by short walking breaks to interrupt sitting.

CONCLUSIONS

In older individuals, three hours of sitting did not influence cognitive performance or cerebral perfusion. However, the sitting period increased blood pressure and cerebrovascular resistance, which are known to negatively impact brain health in the long-term. Importantly, we found that these effects in older individuals cannot be mitigated by higher mental activity and/or regular walking breaks.

TRIAL REGISTRATION

Clinical trial registration URL: https://www.toetsingonline.nl/. Unique identifier: NL64309.091.17. Date of registration: 06-02-2018.

Anthocyanin-Rich New Zealand Blackcurrant Extract Supports the Maintenance of Forearm Blood-Flow During Prolonged Sedentary Sitting

Objectives: We examined the acute effects of anthocyanin-rich New Zealand blackcurrant extract and a placebo on hemodynamics during 120 min of sedentary sitting in healthy males. Additionally, we investigated whether changes in resting hemodynamics altered repeated isometric hand-grip exercise performance and post exercise forearm blood flow (FBF). Methods: Ten healthy males completed two trials during which they ingested either blackcurrant extract (1.87 mg total anthocyanins/kg bodyweight) or placebo powder. Heart rate, blood pressure and forearm blood flow were measured, and venous blood was sampled, prior to and 30, 60, 90 and 120 min-post ingestion. Participants remained seated for the duration of each trial. At 120 min post-ingestion participants completed as many repetitions of isometric hand-grip contractions as possible. Results: Heart rate, blood pressure and mean arterial pressure changed over time (all p < 0.001) but did not differ between treatments. A treatment x time interaction for FBF (p = 0.025) and forearm vascular resistance (FVR) (p = 0.002) was found. No difference in the number of isometric hand-grip contractions was observed between treatments (p = 0.68) nor was there any treatment x time interaction in post-exercise FBF (p = 0.997). Plasma endothelin-1 (p = 0.023) and nitrate (p = 0.047) changed over time but did not differ between treatments (both p > 0.1). Plasma nitrite did not change over time (p = 0.732) or differ between treatments (p = 0.373). Conclusion: This study demonstrated that acute ingestion of a single dose of blackcurrant extract maintained FBF and FVR during an extended period of sitting; however, this did not influence exercise performance during hand-grip exercise.

Local exercise does not prevent the aortic stiffening response to acute prolonged sitting: a randomized crossover trial

Prolonged sitting has been shown to promote endothelial dysfunction in the lower legs. Furthermore, it has been reported that simple sitting-interruption strategies, including calf raises, prevent leg endothelial dysfunction. However, it is unclear whether prolonged sitting affects central cardiovascular health, or whether simple sitting-interruption strategies prevent impaired central cardiovascular health. This study sought to answer two questions: in young, healthy adults 1) does prolonged sitting (3 h) lead to increased aortic stiffness, and 2) do intermittent calf raise exercises to prevent pooling prevent aortic stiffening. Twenty young, healthy participants (21.7 ± 2.5 yr, 70% female, 25.5 ± 6.1 kg/m2) were randomized to 3 h of sitting with (CALF) or without (CON) 10 calf raises every 10 min. Aortic stiffening [carotid-femoral pulse wave velocity (PWV)] was measured in the supine position pre- and post-sitting. Venous pooling during sitting was estimated with total hemoglobin (tHB) concentration using near-infrared spectroscopy. There were no condition × time interactions. Following 3 h of sitting, PWV significantly increased (0.30 ± 0.46 m/s, P < 0.001). There was no condition effect for PWV ( P = 0.694), indicating the intermittent calf rises did not preserve central cardiovascular health. tHb was not significantly affected by sitting ( P = 0.446) but was 1.9 μM higher for CON versus CALF ( P = 0.106). Sitting increases aortic stiffness in young, healthy individuals, a process that may be influenced by lower extremity blood pooling. Calf raises, which have been reported to preserve vascular function in the legs, do not appear to provide sufficient stimulus for maintaining central cardiovascular health.

NEW & NOTEWORTHY Although simple strategies, such as fidgeting or calf raises, are sufficient for preserving vascular function in the legs, data from the current study indicate that such strategies are not sufficient for maintaining central cardiovascular health, which is linked to cardiovascular disease.

Effects of Alternating Standing and Sitting Compared to Prolonged Sitting on Cerebrovascular Hemodynamics

PURPOSE

Previous research suggests that prolonged sitting may acutely reduce cerebral blood flow velocity (CBFv). The purpose of this study was to evaluate the effects of alternating standing and sitting vs prolonged sitting on CBFv.

METHODS

This randomized crossover study enrolled working adults (N=25) with pre-to-stage 1 hypertension not using antihypertensive medications, and a body mass index from 25 to < 40 kg/m2. Subjects participated in two simulated workday conditions: 1) sitting continuously (SIT), and 2) alternating standing and sitting every 30 min (SS). Beat-to-beat systolic, mean and diastolic CBFv were recorded bilaterally for 1 min via insonation of the middle cerebral artery using transcranial Doppler ultrasonography before (morning), between (midday) and following (afternoon) two 3-hr 40 min work periods.

RESULTS

Mean±SD age was 42±12 years, blood pressure (BP) was 132±9/83±8 mmHg, and BMI was 32±5 kg/m2. Cerebrovascular hemodynamics did not differ across condition (P>0.05). There were, however, significant nonlinear effects of time (decrease from morning to midday; increase from midday to afternoon) on systolic CBFv (P=0.014), mean CBFv (P=0.001), diastolic CBFv (P=0.002), and pulsatility index (P=0.038). When overall time effects were evaluated during each time interval, mean and diastolic CBFv significantly decreased morning to midday and all CBFv increased from midday to afternoon. When separated by condition, significant time effects were observed for all CBFv during SIT (P<0.02) but not SS (P>0.05).

CONCLUSIONS

In individuals with elevated BP and BMI, CBFv significantly decreased by midday and increased by afternoon, especially during a workday of prolonged sitting. Future studies should evaluate the combination of frequent walks and a sit-stand desk to break up prolonged sitting.

Changes of blood pressure following initiation of physical inactivity and after external addition of pulses to circulation

PURPOSE

To determine whether an innovative, motorized, wellness device that effortlessly produces physical activity (JD) can mitigate the hypertensive effects of prolonged sitting or lying down.

METHODS

Twenty-two normotensive and hypertensive adults of both genders gave informed consent to participate in a randomized controlled crossover study of a passive simulated jogging device (JD) in both supine and seated postures. Each study participant was monitored with a continuous non-invasive arterial pressure monitoring device (CNAP) over 60 min. The initial 10 min served as baseline for each posture. The subjects were randomized to begin with either JD or SHAM control for 30 min, and monitoring was continued for an additional 10 min in one posture; three days later posture and order of JD or SHAM were changed.

RESULTS

In both seated and supine postures, SHAM was associated with a significant rise in blood pressure (BP) which was observed within 5-10 min; it continued to rise or remain elevated for over a 40-min observation period. In contrast, JD produced a significant decrease in both systolic and diastolic blood pressure in both postures. During recovery in seated posture JD decreased systolic and diastolic BP by - 8.1 and - 7.6 mmHg, respectively. In supine posture, a similar decrease in BP occurred.

CONCLUSIONS

There is rapid onset of increase in systolic and diastolic BP with physical inactivity in both supine and seated postures. Administration of JD significantly decreased BP in both postures. Further studies are needed to assess long-term effectiveness.

Effect of Using a Sit-Stand Desk on Ratings of Discomfort, Fatigue, and Sleepiness Across a Simulated Workday in Overweight and Obese Adults

BACKGROUND

Limited research examines the influence of sit-stand desks on ratings of discomfort, sleepiness, and fatigue. This study evaluated the time course of these outcomes over 1 day.

METHODS

Adults (N = 25) completed a randomized cross-over study in a laboratory with two 8-hour workday conditions: (1) prolonged sitting (SIT) and (2) alternating sitting and standing every 30 minutes (SIT-STAND). Sleepiness was assessed hourly. Discomfort, physical fatigue, and mental fatigue were measured every other hour. Linear mixed models evaluated whether these measures differed across conditions and the workday. Effect sizes were calculated using Cohen's d.

RESULTS

Participants were primarily white (84%) males (64%), with mean (SD) body mass index of 31.9 (5.0) kg/m² and age 42 (12) years. SIT-STAND resulted in decreased odds of discomfort (OR = 0.37, P = .01) and lower overall discomfort (β = -0.19, P < .001, d = 0.42) versus SIT. Discomfort during SIT-STAND was lower in the lower and upper back, but higher in the legs (all Ps< .01, d = 0.26-0.42). Sleepiness (β = -0.09, P = .01, d = 0.15) and physical fatigue (β = -0.34, P = .002, d = 0.34) were significantly lower in SIT-STAND. Mental fatigue was similar across conditions.

CONCLUSIONS

Sit-stand desks may reduce acute levels of sleepiness, physical fatigue, and both overall and back discomfort. However, levels of lower extremity discomfort may be increased with acute exposure.

Interrupting prolonged sitting with brief bouts of light walking or simple resistance activities reduces resting blood pressure and plasma noradrenaline in type 2 diabetes

OBJECTIVE

Prolonged sitting is increasingly recognized as a ubiquitous cardiometabolic risk factor, possibly distinct from lack of physical exercise. We examined whether interrupting prolonged sitting with brief bouts of light-intensity activity reduced blood pressure (BP) and plasma noradrenaline in type 2 diabetes (T2D).

METHODS

In a randomized crossover trial, 24 inactive overweight/obese adults with T2D (14 men; mean ± SD; 62 ± 6 years) consumed standardized meals during 3 × 8 h conditions: uninterrupted sitting (SIT); sitting + half-hourly bouts of walking (3.2 km/h for 3-min) (light-intensity walking); and sitting + half-hourly bouts of simple resistance activities for 3 min (SRAs), each separated by 6-14 days washout. Resting seated BP was measured hourly (mean of three recordings, ≥20-min postactivity). Plasma noradrenaline was measured at 30-min intervals for the first hour after meals and hourly thereafter.

RESULTS

Compared with SIT, mean resting SBP and DBP were significantly reduced (P < 0.001) for both light-intensity walking (mean ± SEM; -14 ± 1/-8 ± 1 mmHg) and SRA (-16 ± 1/-10 ± 1 mmHg), with a more pronounced effect for SRA (P < 0.05 versus light-intensity walking). Similarly, mean plasma noradrenaline was significantly reduced for both light-intensity walking (-0.3 ± 0.1 nmol/l) and SRA (-0.6 ± 0.1 nmol/l) versus SIT, with SRA lower than light-intensity walking (P < 0.05). Mean resting heart rate was lowered by light-intensity walking (-3 ± 1 bpm; P < 0.05), but not SRA (-1 ± 1 bpm).

CONCLUSION

Interrupting prolonged sitting with brief bouts of light-intensity walking or SRA reduces resting BP and plasma noradrenaline in adults with T2D, with SRA being more effective. Given the ubiquity of sedentary behaviors and poor adherence to structured exercise, this approach may have important implications for BP management in patients with T2D.

Effect of prolonged sitting and breaks in sitting time on endothelial function

Sitting time (ST) is associated with cardiovascular disease risk factors, whereas breaking ST has been reported to be beneficial for reducing cardiovascular risk.

PURPOSE

The objective of this study is to examine the effects of breaking ST on superficial femoral artery (SFA) endothelial function.

HYPOTHESES

1) Prolonged sitting would induce endothelial dysfunction and changes in shear forces, and 2) breaking ST with brief periods of activity would prevent attenuation in endothelial function.

METHODS

Twelve nonobese men (24.2 ± 4.2 yr) participated in two randomized 3-h sitting trials. In the sitting (SIT) trial, subjects were seated on a firmly cushioned chair for 3 h without moving their lower extremities. In the breaking ST trial (ACT), subjects sat similar to the SIT trial but walked on a treadmill for 5 min at 2 mph at 30 min, 1 h 30 min, and 2 h 30 min during the sitting interval. SFA flow-mediated dilation (FMD) was assessed at baseline, 1 h, 2 h, and 3 h in each trial. Statistical analyses were performed using dependent variables SFA FMD and shear rates. Significance was set at P ≤ 0.05.

RESULTS

In the SIT trial, there was a significant decline in SFA FMD from baseline to 3 h (baseline, 4.72% ± 3.78%; 1 h, 0.52% ± 0.85%; 2 h, 1.66% ± 1.11%; 3 h, 2.2% ± 2.15; P < 0.05 by ANOVA) accompanied by a decline in mean shear rate and antegrade shear rate but no difference in shear rate (area under the curve). By two-way repeated-measures ANOVA, ACT prevented the sitting-induced decline in FMD (baseline, 4.5% ± 2.3%; 1 h, 5.04% ± 2.85%; 2 h, 5.28% ± 5.05%; 3 h, 6.9% ± 4.5%) along with no decline in shear rates.

CONCLUSION

Three hours of sitting resulted in a significant impairment in shear rate and SFA FMD. When light activity breaks were introduced hourly during sitting, the decline in FMD was prevented.

Impact of prolonged sitting on vascular function in young girls

NEW FINDINGS

What is the central question of this study? Children are spending more than 60% of their waking day sedentary. The consequences of excessive sedentary behaviour are not well understood in the child, but there is growing evidence that with increasing sedentary time, cardiovascular risk in childhood also increases. What is the main finding and its importance? Our findings show that a 3 h period of uninterrupted sitting causes a profound (33%) reduction in vascular function in young girls. Importantly, we also demonstrate that breaking up sitting with regular exercise breaks can prevent this. Excessive sedentary behaviour has serious clinical and public health implications; however, the physiological changes that accompany prolonged sitting in the child are not completely understood. Herein, we examined the acute effect a prolonged period of sitting has upon superficial femoral artery function in 7- to 10-year-old girls and the impact of interrupting prolonged sitting with exercise breaks. Superficial femoral artery endothelium-dependent flow-mediated dilatation, total shear rate, anterograde and retrograde shear rates and oscillatory shear index were assessed before and after two experimental conditions: a 3 h uninterrupted period of sitting (SIT) and a 3 h period of sitting interrupted each hour with 10 min of moderate-intensity exercise (EX). A mixed-model analysis of variance was used to compare between-condition and within-condition main effects, controlling for the within-subject nature of the experiment by including random effects for participant. Superficial femoral artery endothelium-dependent flow-mediated dilatation decreased significantly from pre- to post-SIT (mean difference 2.2% flow-mediated dilatation; 95% confidence interval = 0.60-2.94%, P < 0.001). This relative decline of 33% was abolished in the EX intervention. Shear rates were not significantly different within conditions. Our data demonstrate the effectiveness of short but regular exercise breaks in offsetting the detrimental effects of uninterrupted sitting in young girls.

Antioxidant vitamin C prevents decline in endothelial function during sitting

BACKGROUND

This study was designed to test the hypothesis that antioxidant Vitamin C prevents the impairment of endothelial function during prolonged sitting.

MATERIAL AND METHODS

Eleven men (24.2 ± 4.4 yrs) participated in 2 randomized 3-h sitting trials. In the sitting without vitamin C (SIT) and the sitting with vitamin C (VIT) trial, participants were seated for 3 h without moving their legs. Additionally, in the VIT trial, participants ingested 2 vitamin C tablets (1 g and 500 mg) at 30 min and 1 h 30 min, respectively. Superficial femoral artery (SFA) flow-mediated dilation (FMD) was measured hourly for 3 h.

RESULTS

By a 1-way ANOVA, there was a significant decline in FMD during 3 h of SIT (p<0.001). Simultaneously, there was a significant decline in antegrade (p=0.04) and mean (0.037) shear rates. For the SIT and VIT trials by a 2-way (trial x time) repeated measures ANOVA, there was a significant interaction (p=0.001). Pairwise testing revealed significant between-SFA FMD in the SIT and VIT trial at each hour after baseline, showing that VIT prevented the decline in FMD 1 h (p=0.009), 2 h (p=0.016), and 3 h (p=0.004). There was no difference in the shear rates between SIT and VIT trials (p>0.05).

CONCLUSIONS

Three hours of sitting resulted in impaired SFA FMD. Antioxidant Vitamin C prevented the decline in SFA FMD, suggesting that oxidative stress may contribute to the impairment in endothelial function during sitting.

Breaking up prolonged sitting reduces resting blood pressure in overweight/obese adults

AIM

To compare the effect of 7 h of prolonged sitting on resting blood pressure with a similar duration of sitting combined with intermittent brief bouts of light-intensity or moderate-intensity physical activity.

METHODS AND RESULTS

Overweight/obese adults (n = 19; aged 45-65 years) were recruited for a randomized three-treatment crossover trial with a one-week washout between treatments: 1) uninterrupted sitting; 2) sitting with 2 min bouts of light-intensity walking at 3.2 km/h every 20 min; and, 3) sitting with 2 min bouts of moderate-intensity walking at between 5.8 and 6.4 km/h every 20 min. After an initial 2 h period seated, participants consumed a test meal (75 g carbohydrate, 50 g fat) and completed each condition over the next 5 h. Resting blood pressure was assessed oscillometrically every hour as a single measurement, 5 min prior to each activity bout. GEE models were adjusted for sex, age, BMI, fasting blood pressure and treatment order. After adjustment for potential confounding variables, breaking up prolonged sitting with light and moderate-intensity activity breaks was associated with lower systolic blood pressure [light: 120 ± 1 mmHg (estimated marginal mean ± SEM), P = 0.002; moderate: 121 ± 1 mmHg, P = 0.02], compared to uninterrupted sitting (123 ± 1 mmHg). Diastolic blood pressure was also significantly lower during both of the activity conditions (light: 76 ± 1 mmHg, P = 0.006; moderate: 77 ± 1 mmHg, P = 0.03) compared to uninterrupted sitting (79 ± 1 mmHg). No significant between-condition differences were observed in mean arterial pressure or heart rate.

CONCLUSION

Regularly breaking up prolonged sitting may reduce systolic and diastolic blood pressure.

TRIAL REGISTRATION NUMBER

ACTRN12609000656235 (http://www.anzctr.org.au) TRIAL REGISTRATION DATE: August 4th 2009.

Sitting and endothelial dysfunction: the role of shear stress

Sedentary activity is a modifiable life-style behavior and a key component in the etiology of atherosclerotic cardiovascular disease (ACVD). US adults and children spend more than half their waking time in sedentary pursuits. Sedentary activity has been shown to result in impaired insulin sensitivity, impaired metabolic function and attenuated endothelial function, which are classic markers of ACVD. Sedentary activity is defined as 'sitting without otherwise being active.' This behavior promotes reduced muscular activity of the lower extremities which decreases leg blood flow, increases blood pooling in the calf, augments mean arterial pressure, and deforms arterial segments resulting in low mean shear stress (SS). SS activates distinct physiological mechanisms which have been proposed to be protective against ACVD; specifically through a SS-induced endothelium-derived nitric oxide mechanism. Reduced bioavailability of nitric oxide creates a pro-oxidant milieu resulting in increased oxidative stress. There is sufficient evidence which demonstrates that endothelial function is attenuated in the presence of oxidative stress. Sedentary activity results in low SS in the lower extremities which may result in increased oxidative stress and impaired endothelial function. This review furthers the use of sitting as model to study the effects of inactivity, discusses possible physiological mechanisms and suggests future directions.

Susceptibility-weighted imaging: clinical angiographic applications

By combining filtered phase and magnitude information to create a novel and intrinsic source of contrast, susceptibility-weighted imaging (SWI) has shown great promise in clinical angiography and venography. SWI has contributed to new insights into traumatic brain injury, the role of calcification in atherosclerosis, and the possible relationship between blood settling and deep venous thrombosis. A further contribution from SWI to deep venous thrombosis research (and also stroke) involves its application to the noninvasive measurement of oxygen saturation in the brain and in other tissues. Altogether, SWI offers manifold and diverse avenues for further research using angiographic and venographic techniques.

Neuromuscular electrical stimulation and an ottoman-type seat effectively improve popliteal venous flow in a sitting position

The aim of this study was to examine the effects of the sitting posture on the lower limb venous flow and to explore the beneficial effects of neuromuscular electrical stimulation (NMES) and an ottoman-type seat on the venous flow. Healthy adult volunteers without a history of lower limb surgery or thromboembolism were recruited, and the flow velocity, cross-sectional area, and flow volume of the popliteal vein were measured using Doppler ultrasound. A posture change from the prone position to the sitting position on the ottoman-type seat decreased the flow velocity and increased the cross-sectional area of the popliteal vein, and the flow volume was not altered over 120 min. The flow velocity was further decreased, and the cross-sectional area was further increased by subjects sitting on a regular driving seat when compared with the values obtained with an ottoman-type seat. The popliteal flow velocity in the NMES leg was significantly higher than in the non-NMES leg throughout the 120-min testing in the sitting position, but no difference in the cross-sectional area was found between the NMES and the non-NMES legs. Thus lower limb venous stasis elicited by the sitting posture was improved by the ottoman-type seat and NMES.

Difference in the cardiovascular response to prolonged sitting in men and women

Orthostatic stress, sitting, results in adjustments of cardiovascular variables to maintain blood pressure and is prominent in a variety of occupations. Sitting serves as the control position for head-out water immersion studies. This study addressed gender differences in the cardiovascular response to prolonged sitting. Ten men and 10 women had cardiovascular measurements in the supine position compared with measurements during 2 hours in the seated position (Sit). Supine cardiovascular measurements were similar for both sexes. Heart rate changed similarly for both sexes with Sit. With Sit, men had elevated mean arterial pressure (9 +/- 3%), total peripheral resistance (54 +/- 9%), and decreased cardiac index (-27 +/- 5%), while women had no change in mean arterial pressure, lesser elevations in total peripheral resistance (17 +/- 7%), and lesser decreases in cardiac index (-12 +/- 5%) than men. Thus men, compared to women, had an elevated mean arterial pressure response to prolonged orthostatic stress.