Potential Moderating Role of Upper Extremity Activity on Metabolic Effects of Sedentary Behavior in People With Stroke

In light of recent PTJ articles on sedentary behavior,^1–3 I want to begin a discussion about the potential moderating role of upper extremity (UE) activity on the metabolic effects of sedentary behavior in people with stroke. A great deal of research has demonstrated the cardiovascular and metabolic benefits of physical activity,⁴ resulting in poststroke physical activity and exercise recommendations⁵ to counter the low levels of physical activity observed in people with stroke.^6,7 In recent years, sedentary behavior, defined as low energy expenditure while sitting or lying down,² has received increasing attention because sedentary behavior affects lipid and glucose metabolism independent of physical activity.⁸ Because decreased sedentary behavior is associated with decreased metabolic risk,⁹ interventions to decrease sitting behavior and increase standing and leisure-based physical activity have been promoted.^1,10 For individuals with severe stroke-related mobility impairment, however, increasing time spent standing and ambulating may not be an option. Is it possible for UE activity to moderate the metabolic effects of sedentary behavior in these individuals?

In a recent study, English et al³ demonstrated that adults with stroke spent 77% (10.9 hours) of waking hours sitting. Other studies showed even higher values of daily sedentary behavior in people with stroke (ie, 81%–85%), although these studies did not distinguish between sitting and lying down.^11–13 Despite these high percentages of sedentary behavior, UE activity is relatively high in people with stroke. Michielsen et al reported that during a typical day the UEs of community-dwelling adults with stroke were active 37% of the time while seated and 40% of the time overall,¹¹ and Bailey et al found that the UEs were active for 32% of the time during a typical day.¹⁴ Given that the UEs are active throughout the day in people with stroke, is it possible that UE activity in people with stroke can reach sufficient intensity to offset the negative effects of sedentary activity on lipid and glucose metabolism?

To my knowledge, this question has not yet been directly examined. One could argue that individuals with severe, stroke-related UE impairment are not capable of achieving UE activity of sufficient intensity to evoke a metabolic effect. Previous research, however, has demonstrated that physiologic capacity (as measured by maximal oxygen consumption) is lower in adults with stroke than in adults without stroke¹⁵; thus, an individual with stroke will exert more energy than an individual without stroke to perform the same task. Due to the increased physiologic demands after stroke, perhaps it is possible that metabolic benefits may be gained at lower intensities of UE activity such as those that occur during the routine performance of activities of daily living.

Moving forward, wrist-worn accelerometry may be a helpful tool for examining this question. Wrist-worn accelerometry is appealing because it captures UE activity that occurs while sitting, which would otherwise go unmeasured by hip-worn accelerometers. In the realm of hip-worn accelerometers, thresholds for sedentary behavior and light-, moderate-, and vigorous-intensity physical activity have been developed using accelerometry output and validated against maximal oxygen consumption during treadmill walking.¹⁶ Validation of wrist-worn accelerometry output against a direct physiological measure will be necessary to determine whether a threshold for UE activity exists, above which the metabolic effects of sedentary behavior can be attenuated. It must be remembered, however, that physiologic capacity is decreased after stroke, which increases the energy demands of activity performance. Thus, thresholds for intensity of UE activity must be validated in people with stroke independently of adults who are not disabled.

In summary, the effects of sedentary behavior on glucose and lipid metabolism are independent of physical activity, which necessitates interventions to decrease sedentary behavior. People with stroke have high levels of sedentary behavior, which places them at increased risk for cardiometabolic disease and mortality. For those individuals who experience mobility impairment, increasing time spent standing or ambulating may not be possible; therefore, other interventions are needed. Increasing UE activity may be a feasible alternative, but research has not yet examined whether UE activity can moderate the metabolic effects of sedentary behavior. This is a question with important implications for people with stroke, clinicians, and researchers alike.

• © 2016 American Physical Therapy Association