Taking steps in the workplace to improve vascular function

The number of sedentary jobs in contemporary societies has increased dramatically in the last 50 years such that occupations requiring at least moderate levels of physical activity now make up a small percentage of the total workforce (Church et al. 2011). It is now recognized that sedentary behaviour is positively associated with an increase in the incidence of cardiovascular disease (CVD); however, the specific mechanisms linking prolonged sitting (a common form of sedentary behaviour in the workplace) to increased CVD risk are less clear. Given the rise in the number of sedentary jobs and the resulting decline in physical activity within the workplace, understanding these mechanisms is critical in order to create effective interventions that mitigate the risks associated with this emerging ‘occupational hazard’. In this issue of Experimental Physiology, Restaino et al. (2015) make an important contribution to the understanding of these mechanisms by studying the negative influence of prolonged sitting on vascular function and the role that increased physical activity might play in reducing vascular dysfunction due to prolonged sitting in the workplace. To understand how sedentary behaviour may impact vascular function in an office setting, Restaino et al. (2015) performed a well-controlled experiment, in which subjects were asked to remain in a seated position for 6 h. Subjects were allowed free use of their arms for office-related activities, such as reading and typing, but were prohibited from moving their legs. Vascular function was assessed at baseline and again after 6 h of uninterrupted sitting in the upper and lower extremities using flow-mediated dilatation and reactive hyperaemia to isolate the effects on macroand microvascular function, respectively. Prolonged sitting reduced blood flow and impaired both measures of vascular function in the lower limbs but selectively impaired only microvascular function in the upper limbs. Most importantly, 10 min of light-intensity walking exercise completely restored vascular function in the lower limbs but did not reverse upper limb microvascular dysfunction. The study by Restaino et al. (2015) provides valuable insight by demonstrating that prolonged sitting differentially influences vascular function in a limb-specific manner and raises important questions regarding the role that physical activity might play in mitigating the effects of sitting on vascular function that will guide future research in this area. Interestingly, the decrease in forearm microvascular function observed by Restaino et al. (2015) was not reversible by 10 min of light walking, suggesting that local increases in blood flow to exercising tissue may be necessary to reverse these microvascular impairments. This is important because forearm microvascular dysfunction is related to increased CVD risk, and the results of this study suggest that 10 min of light walking might not be a sufficient stimulus to eliminate the impact of sedentary behaviour on non-exercising vascular beds. Whether or not forearm microvascular function would have been improved by higher intensity and/or longer duration walking is unknown. Systemic improvement in vascular function within non-exercising vascular beds, such as the forearm microvasculature, is a well-established adaptation to lower limb aerobic exercise (Green et al. 2002); thus, more vigorous activity might be necessary to reduce all of the vascular risks associated with sedentary behaviour. Even if a single bout of higher intensity exercise could improve vascular function in non-exercising limbs, it may not be enough to counteract the risk of CVD associated with prolonged sitting. Individuals who exceed daily physical activity guidelines, but lead otherwise sedentary lives, do not appear to be protected from the increased mortality risk associated with sedentary behaviour (Katzmarzyk et al. 2009). As Restaino et al. (2015) point out in the highlighted article, it is presently unclear whether a single uninterrupted period of sitting imparts a greater CVD risk than interrupting sedentary behaviour with brief periods of physical activity. To this end, Thosar et al. (2015) recently reported a reduction in lower limb conduit artery function following 3 h of uninterrupted sitting that was prevented when sitting time was interrupted each hour by brief, 5 min bouts of light-intensity physical activity; however, the effects on non-exercising vascular beds, such as the forearm microvasculature, were not assessed in this study. The highlighted paper by Restaino et al. (2015) brings to light the importance of considering multiple vascular beds when studying how exercise influences vascular dysfunction associated with prolonged sitting. There is presently no direct evidence linking lower limb vascular dysfunction with increased CVD risk, and impairments to non-exercising limbs may be an important contributor to the overall CVD risk associated with prolonged sitting. Nevertheless, the vasculature of the lower limbs is more susceptible to atherosclerotic disease, and light walking appears to reverse the impairment in lower limb vascular function; thus, it could be argued that even some level of physical activity in the workplace could be beneficial. Our understanding of how sedentary behaviour impacts vascular function and health is still in its infancy. Sedentary behaviour is a modifiable lifestyle factor, and future work in this field will undoubtedly need to uncover feasible intervention strategies to dissociate the effects of prolonged sitting on increased CVD risk. Moreover, future strategies will need to take into consideration populations that are already at heightened risk for developing CVD due to impaired baseline vascular function. Individuals with chronic diseases as well as midlife adults (i.e. working adults with age-associated impairments in vascular function) may be more prone to sedentary behaviour and more vulnerable to the added CVD risk associated with sitting than the young healthy subjects studied in the highlighted paper. Nevertheless, the findings by Restaino et al. (2015) represent a good first step in understanding the physiology related to prolonged sitting and vascular dysfunction and will guide future discoveries in this rapidly growing field.