Introduction
Physical inactivity and sedentary behavior affect cardiorespiratory fitness and are associated with cardiometabolic risk factors.^1,2 Adults can meet or exceed physical activity recommendations but still spend most hours sitting. Observational studies find associations between sitting time or physical inactivity and cardiovascular mortality.³ The COVID-19 pandemic led to long periods of self-isolation, worsened sedentary behavior, and reduced routine physical activity. Clearly, there is an urgent need to provide recommendations for patients unable to meet physical activity recommendations. Dunstan et al. reviewed strengths and limitations of the experimental and observational evidence on the adverse cardiometabolic outcomes of sedentary behaviors, highlighted mechanisms underlying the risk, and suggested steps to improve deleterious behaviors.⁴

What is the evidence of the health implications of excessive sitting?
The NHANES study, using self-reported data, suggests that the proportion of individuals who do not meet physical activity recommendations and spend >6 hours sitting per day has increased from 16% in 2007-2008 to 19% in 2015-2016.⁵ As this result was based on self-reported variables, sedentary time could be 7.7-11.5 hours per day.^6-8 In an observational study involving >3,000 adults, every 30 minute increment in daily physical activity – irrespective of intensity level – was associated with 11% and 36% risk reduction of cardiovascular disease (CVD) and all-cause mortality, respectively.⁹ Conversely, every 1-hour per day increment in sedentary time was associated with a 33% risk increase of CVD or all-cause mortality.⁹ Thus, higher levels of physical activity, regardless of intensity, are associated with better cardiorespiratory fitness and CVD outcomes.

How is increased sitting time associated with cardiometabolic risk?
Prolonged sitting periods increase the risk of vascular dysfunction, hypertension, impaired glucose level, and endothelial dysfunction. In a meta-analysis prolonged sitting led to decreased flow-mediated dilatation.¹⁰ Likewise, interruption of prolonged periods of sitting by activity improved flow-mediated dilatation. Several studies showed reduced metabolic demand and decreased blood flow during prolonged sitting, which leads to hypertension,¹¹ especially in individuals with obesity and type 2 diabetes.¹¹ However, many studies have shown the reverse phenomenon of decreased blood pressure when sitting time is interrupted by physical activities.^12,13

Prolonged sitting is associated with acute hyperglycemia and hyperinsulinemia, which leads to further vascular dysfunction.¹⁴ Another meta-analysis showed improved glycemia regulation and decreased insulin with regular interruptions of prolonged sitting periods.¹⁵ These benefits were more prominent in physically inactive individuals and those with diabetes or obesity.¹⁶ In summary, interruption of prolonged sitting with regular, brief physical activity can reduce cardiometabolic risk factors.

Does prolonged sitting time predispose to exercise inertia or resistance?
Prolonged sitting for 4 days blunts the typical dose-response of cardioprotective benefits of exercise and predisposes to exercise inertia.^17,18 Interruption of sitting by physical activities leads to improvement in metabolic parameters and diminishes negative cardioprotective effects of sitting, thus improving exercise resistance.

What is the outcome of sedentary behavior reduction trials?
Since 2003, over 30 controlled intervention trials were conducted to reduce sedentary behavior in adults.¹⁹ These interventions included environmental or educational/motivational targets or a combination of both. Only the environmental and combination interventions had clinically relevant effects.²⁰ Modelling the effects of replacing 30 minutes of sitting time with light physical activity was associated with a 2-4% reduction in major cardiovascular risk factors.^21,22 However, these effects were larger for individuals with workplace interventions.²³ These trials did not include diverse populations and the interventions were brief (<12 months); therefore, additional studies are needed to evaluate sustained and long-term effectiveness of interventions to target sedentary behavior in high-risk patients.

What is the concept of sitting less and moving more?
The association between excessive sitting and adverse CV outcome is more pronounced in physically inactive individuals. Replacing such behavior with moderate to vigorous intensity physical activities reduces CVD risk. A meta-analysis including >1 million participants showed that those with high levels of moderate intensity physical activity (40-60 mins moderate intensity exercise daily) have low risk of CVD despite excessive sedentary behavior.²⁴ Therefore, any form of exercise seems to be beneficial.

What are the future implications of these studies?
Awareness of the effects of physical inactivity and sedentary behavior on all-cause mortality and CVD outcomes has increased the interest of researchers and clinicians in the underlying pathophysiology, which may help to design a behavior-based strategy to reduce CVD risk. The authors recommend embracing the idea of "move more and sit less during the day" and help to spread the message of therapeutic benefits of exercise.⁴

The COVID-19 pandemic led to long periods of self-isolation and created a situation that further increased sedentary behavior. Even during pandemics, active people should maintain their routine exercise or adapt it so they can perform their exercise at home. Adults who are unable to meet the recommended physical activity should engage in regular physical activity and decrease sitting time to reduce their CVD risk.

The body of evidence needs to be developed and further consolidated to inform future clinical guidelines on sedentary behavior and CV health, particularly on dose-response relationships and on appropriate quantitative change targets. Technological advances in consumer wearable devices provide new opportunities to measure the impact of physical activity interventions. This development can overcome challenges of self-reported variables, improve efficiency of data collection, and could deliver new insights.

This review article provides comprehensive evidence of the deleterious effects of sedentary time, endorses broader prescription of reducing physical inactivity time and encourages clinicians to embrace a more active role in identifying and advising vulnerable patients.⁴ Although there is a lot of evidence emphasizing the detrimental effects of physical inactivity, the adoption of strategies to change this seems to be low. While maintaining physical activity is endorsed by various guidelines, there are few recommendations to reduce sedentary time. Initiatives should be developed to understand the obstacles faced by physicians and patients to adopt these evidence-based recommendations.

References

1. Booth FW, Roberts CK, Thyfault JP, Ruegsegger GN, Toedebusch RG. Role of inactivity in chronic diseases: evolutionary insight and pathophysiological mechanisms. Physiol Rev 2017;97:1351-402.
2. Tremblay MS, Aubert S, Barnes JD, et al. Sedentary Behavior Research Network (SBRN) - terminology consensus project process and outcome. Int J Behav Nutr Phys Act 2017;14:75.
3. Katzmarzyk PT, Powell KE, Jakicic JM, Troiano RP, Piercy K, Tennant B. Sedentary behavior and health: update from the 2018 Physical Activity Guidelines Advisory Committee. Med Sci Sports Exerc 2019;51:1227-41.
4. Dunstan DW, Dogra S, Carter SE, Owen N. Sit less and move more for cardiovascular health: emerging insights and opportunities. Nat Rev Cardiol 2021;18:637-48.
5. Du Y, Liu B, Sun Y, Snetselaar LG, Wallace RB, Bao W. Trends in adherence to the physical activity guidelines for Americans for aerobic activity and time spent on sedentary behavior among US adults, 2007 to 2016. JAMA Netw Open 2019;2:e197597.
6. Ekelund U, Tarp J, Steene-Johannessen J, et al. Dose-response associations between accelerometry measured physical activity and sedentary time and all cause mortality: systematic review and harmonised meta-analysis. BMJ 2019;366:l4570.
7. Matthews CE, Chen KY, Freedson PS, et al. Amount of time spent in sedentary behaviors in the United States, 2003-2004. Am J Epidemiol 2008;167:875-81.
8. Matthews CE, Keadle SK, Troiano RP, et al. Accelerometer-measured dose-response for physical activity, sedentary time, and mortality in US adults. Am J Clin Nutr 2016;104:1424-32.
9. Ballin M, Nordström P, Niklasson J, Nordström A. Associations of objectively measured physical activity and sedentary time with the risk of stroke, myocardial infarction or all-cause mortality in 70-year-old men and women: a prospective cohort study. Sports Med 2021;51:339-49.
10. Paterson C, Fryer S, Zieff G, et al. The effects of acute exposure to prolonged sitting, with and without interruption, on vascular function among adults: a meta-analysis. Sports Med 2020;50:1929-42.
11. Dempsey PC, Larsen RN, Dunstan DW, Owen N, Kingwell BA. Sitting less and moving more: implications for hypertension. Hypertension 2018;72:1037-46.
12. Dempsey PC, Sacre JW, Larsen RN, et al. Interrupting prolonged sitting with brief bouts of light walking or simple resistance activities reduces resting blood pressure and plasma noradrenaline in type 2 diabetes. J Hypertens 2016;34:2376-82.
13. Wheeler MJ, Dunstan DW, Ellis KA, et al. Effect of morning exercise with or without breaks in prolonged sitting on blood pressure in older overweight/obese adults. Hypertension 2019;73:859-67.
14. Carter S, Hartman Y, Holder S, Thijssen DH, Hopkins ND. Sedentary behavior and cardiovascular disease risk: mediating mechanisms. Exerc Sport Sci Rev 2017;45:80-6.
15. Loh R, Stamatakis E, Folkerts D, Allgrove JE, Moir HJ. Effects of interrupting prolonged sitting with physical activity breaks on blood glucose, insulin and triacylglycerol measures: a systematic review and meta-analysis. Sports Med 2020;50:295-330.
16. Crespo NC, Mullane SL, Zeigler ZS, Buman MP, Gaesser GA. Effects of standing and light-intensity walking and cycling on 24-h glucose. Med Sci Sports Exerc 2016;48:2503-11.
17. Akins JD, Crawford CK, Burton HM, Wolfe AS, Vardarli E, Coyle EF. Inactivity induces resistance to the metabolic benefits following acute exercise. J Appl Physiol (1985) 2019;126:1088-94.
18. Kim IY, Park S, Chou TH, Trombold JR, Coyle EF. Prolonged sitting negatively affects the postprandial plasma triglyceride-lowering effect of acute exercise. Am J Physiol Endocrinol Metab 2016;311:E891-e98.
19. Peachey MM, Richardson J, Tang AV, Dal-Bello Haas V, Gravesande J. Environmental, behavioural and multicomponent interventions to reduce adults' sitting time: a systematic review and meta-analysis. Br J Sports Med 2020;54:315-25.
20. Healy GN, Matthews CE, Dunstan DW, Winkler EA, Owen N. Sedentary time and cardio-metabolic biomarkers in US adults: NHANES 2003-06. Eur Heart J 2011;32:590-97.
21. Buman MP, Winkler EAH, Kurka JM, et al. Reallocating time to sleep, sedentary behaviors, or active behaviors: associations with cardiovascular disease risk biomarkers, NHANES 2005-2006. Am J Epidemiol 2014;179:323-34.
22. Hadgraft NT, Winkler E, Climie RE, et al. Effects of sedentary behaviour interventions on biomarkers of cardiometabolic risk in adults: systematic review with meta-analyses. Br J Sports Med 2021;55:144-54.
23. Mulchandani R, Chandrasekaran AM, Shivashankar R, et al. Effect of workplace physical activity interventions on the cardio-metabolic health of working adults: systematic review and meta-analysis. Int J Behav Nutr Phys Act 2019;16:134.
24. Ekelund U, Steene-Johannessen J, Brown WJ, et al. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women. Lancet 2016;388:1302-10.

Clinical Topics: Cardiovascular Care Team, COVID-19 Hub, Diabetes and Cardiometabolic Disease, Dyslipidemia, Prevention, Exercise, Hypertension

Keywords: Dyslipidemias, Sedentary Behavior, Cardiovascular Diseases, Insulin, Self Report, Diabetes Mellitus, Type 2, Nutrition Surveys, Pandemics, Blood Pressure, COVID-19, SARS-CoV-2, Risk Factors, Exercise, Hyperglycemia, Hyperinsulinism, Risk Reduction Behavior, Hypertension, Obesity, Prescriptions

< Back to Listings