Robyn N. Larsen

Breaking Up Prolonged Sitting Reduces Postprandial Glucose and Insulin Responses

OBJECTIVE Observational studies show breaking up prolonged sitting has beneficial associations with cardiometabolic risk markers, but intervention studies are required to investigate causality. We examined the acute effects on postprandial glucose and insulin levels of uninterrupted sitting compared with sitting interrupted by brief bouts of light- or moderate-intensity walking. RESEARCH DESIGN AND METHODS Overweight/obese adults (n = 19), aged 45–65 years, were recruited for a randomized three-period, three-treatment acute crossover trial: 1) uninterrupted sitting; 2) seated with 2-min bouts of light-intensity walking every 20 min; and 3) seated with 2-min bouts of moderate-intensity walking every 20 min. A standardized test drink was provided after an initial 2-h period of uninterrupted sitting. The positive incremental area under curves (iAUC) for glucose and insulin (mean [95% CI]) for the 5 h after the test drink (75 g glucose, 50 g fat) were calculated for the respective treatments. RESULTS The glucose iAUC (mmol/L) ⋅ h after both activity-break conditions was reduced (light: 5.2 [4.1–6.6]; moderate: 4.9 [3.8–6.1]; both P < 0.01) compared with uninterrupted sitting (6.9 [5.5–8.7]). Insulin iAUC (pmol/L) ⋅ h was also reduced with both activity-break conditions (light: 633.6 [552.4–727.1]; moderate: 637.6 [555.5–731.9], P < 0.0001) compared with uninterrupted sitting (828.6 [722.0–950.9]). CONCLUSIONS Interrupting sitting time with short bouts of light- or moderate-intensity walking lowers postprandial glucose and insulin levels in overweight/obese adults. This may improve glucose metabolism and potentially be an important public health and clinical intervention strategy for reducing cardiovascular risk.

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.

Benefits for Type 2 Diabetes of Interrupting Prolonged Sitting With Brief Bouts of Light Walking or Simple Resistance Activities

OBJECTIVE To determine whether interrupting prolonged sitting with brief bouts of light-intensity walking (LW) or simple resistance activities (SRA) improves postprandial cardiometabolic risk markers in adults with type 2 diabetes (T2D). RESEARCH DESIGN AND METHODS In a randomized crossover trial, 24 inactive overweight/obese adults with T2D (14 men 62 ± 6 years old) underwent the following 8-h conditions on three separate days (with 6–14 days washout): uninterrupted sitting (control) (SIT), sitting plus 3-min bouts of LW (3.2 km · h−1) every 30 min, and sitting plus 3-min bouts of SRA (half-squats, calf raises, gluteal contractions, and knee raises) every 30 min. Standardized meals were consumed during each condition. Incremental areas under the curve (iAUCs) for glucose, insulin, C-peptide, and triglycerides were compared between conditions. RESULTS Compared with SIT, both activity-break conditions significantly attenuated iAUCs for glucose (SIT mean 24.2 mmol · h · L−1 [95% CI 20.4–28.0] vs. LW 14.8 [11.0–18.6] and SRA 14.7 [10.9–18.5]), insulin (SIT 3,293 pmol · h · L−1 [2,887–3,700] vs. LW 2,104 [1,696–2,511] and SRA 2,066 [1,660–2,473]), and C-peptide (SIT 15,641 pmol · h · L−1 [14,353–16,929] vs. LW 11,504 [10,209–12,799] and SRA 11,012 [9,723–12,301]) (all P < 0.001). The iAUC for triglycerides was significantly attenuated for SRA (P < 0.001) but not for LW (SIT 4.8 mmol · h · L−1 [3.6–6.0] vs. LW 4.0 [2.8–5.1] and SRA 2.9 [1.7–4.1]). CONCLUSIONS Interrupting prolonged sitting with brief bouts of LW or SRA attenuates acute postprandial glucose, insulin, C-peptide, and triglyceride responses in adults with T2D. With poor adherence to structured exercise, this approach is potentially beneficial and practical.

Breaking up of prolonged sitting over three days sustains, but does not enhance, lowering of postprandial plasma glucose and insulin in overweight and obese adults

To compare the cumulative (3-day) effect of prolonged sitting on metabolic responses during a mixed meal tolerance test (MTT), with sitting that is regularly interrupted with brief bouts of light-intensity walking. Overweight/obese adults (n=19) were recruited for a randomized, 3-day, outpatient, cross-over trial involving: (1) 7-h days of uninterrupted sitting (SIT); and (2) 7-h days of sitting with light-intensity activity breaks [BREAKS; 2-min of treadmill walking (3.2 km/h) every 20 min (total: 17 breaks/day)]. On days 1 and 3, participants underwent a MTT (75 g of carbohydrate, 50 g of fat) and the incremental area under the curve (iAUC) was calculated from hourly blood samples. Generalized estimating equation (GEE) models were adjusted for gender, body mass index (BMI), energy intake, treatment order and pre-prandial values to determine effects of time, condition and time × condition. The glucose iAUC was 1.3 ± 0.5 and 1.5 ± 0.5 mmol·h·l(-1) (mean differences ± S.E.M.) higher in SIT compared with BREAKS on days 1 and 3 respectively (condition effect: P=0.001), with no effect of time (P=0.48) or time × condition (P=0.8). The insulin iAUC was also higher on both days in SIT (day 1: ∆151 ± 73, day 3: ∆91 ± 73 pmol·h·l(-1), P=0.01), with no effect of time (P=0.52) or time × condition (P=0.71). There was no between-treatment difference in triglycerides (triacylglycerols) iAUC. There were significant between-condition effects but no temporal change in metabolic responses to MTT, indicating that breaking up of sitting over 3 days sustains, but does not enhance, the lowering of postprandial glucose and insulin.

Acute effects of breaking up prolonged sitting on fatigue and cognition: A pilot study

Objectives To compare the acute effects of uninterrupted sitting with sitting interrupted by brief bouts of light-intensity walking on self-reported fatigue, cognition, neuroendocrine biomarkers and cardiometabolic risk markers in overweight/obese adults. Design Randomised two-condition crossover trial. Setting Laboratory study conducted in Melbourne, Australia. Participants 19 overweight/obese adults (45–75 years). Interventions After an initial 2 h period seated, participants consumed a meal-replacement beverage and completed (on 2 days separated by a 6-day washout period) each condition over the next 5 h: uninterrupted sitting (sedentary condition) or sitting with 3 min bouts of light-intensity walking every 30 min (active condition). Primary outcome measures Self-reported fatigue, executive function and episodic memory at 0 h, 4 h and 7 h. Secondary outcome measures Neuroendocrine biomarkers and cardiometabolic risk markers (blood collections at 0 h, 4 h and 7 h, blood pressure and heart rate measured hourly and interstitial glucose measured using a continuous glucose monitoring system). Results During the active condition, fatigue levels were lower at 4 h (−13.32 (95% CI −23.48 to −3.16)) and at 7 h (−10.73 (95% CI −20.89 to −0.58)) compared to the sedentary condition. Heart rate was higher at 4 h (4.47 (95% CI 8.37 to 0.58)) and at 7 h (4.32 (95% CI 8.21 to 0.42)) during the active condition compared to the sedentary condition. There were no significant differences between conditions by time for other variables. In the sedentary condition, changes in fatigue scores over time correlated with a decrease in heart rate and plasma dihydroxyphenylalanine (DOPA) and an increase in plasma dihydroxyphenylglycol (DHPG). Conclusions Interrupting prolonged sitting with light-intensity walking breaks may be an effective fatigue countermeasure acutely. Fatigue levels corresponded with the heart rate and neuroendocrine biomarker changes in uninterrupted sitting in this pilot study. Further research is needed to identify potential implications, particularly for the occupational health context. Trial registration number ACTRN12613000137796; Results.

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.

Does the type of activity “break” from prolonged sitting differentially impact on postprandial blood glucose reductions? An exploratory analysis

Frequent breaks in prolonged sitting are associated beneficially with glycaemic control. However, the contribution of energy expenditure to this relationship has not been well characterised. In this exploratory analysis, data from 3 laboratory trials that standardised test meals, cohort characteristics (overweight/obese, sedentary), and break frequency and duration were pooled. Higher energy expenditures of different types of breaks (standing, light- or moderate-intensity walking) were associated with lower postprandial glucose and insulin responses in a dose-dependent manner.

The sugar content of soft drinks in Australia, Europe and the United States

Five samples of each soft drink from each region were analysed. * P < 0.05 v US concentration; y P < 0.05 v European concentration. The full data for the concentrations of glucose, fructose, and sucrose, and of total glucose and total fructose in each drink is included in the online Appendix. u Dlimit the drinking of sugar-sweetened beverages (SSBs), Australians are particularly high consumers of such products. In the report of the Australian Health Survey, 39% of males and 29% of females over 2 years of age had consumed SSBs on the day prior to the interview in 2011e2012, and these drinks were the largest sources of sugar in the Australian diet.

Prolonged Uninterrupted Sitting Elevates Postprandial Hyperglycaemia Proportional to Degree of Insulin Resistance

Prolonged uninterrupted sitting is related adversely to cardiometabolic risk markers and postprandial hyperglycaemia, relative to sitting interrupted by regular brief activity breaks. However, whether the magnitude of hyperglycaemic responses to prolonged sitting is dependent upon the underlying degree of insulin resistance remains unclear. Data were pooled from 3 randomized cross‐over laboratory‐based trials (n = 62) that examined the postprandial blood glucose‐ and insulin‐lowering effects of prolonged sitting vs sitting interrupted by regular brief activity breaks in overweight/obese adults who had normal or impaired glucose metabolism (2 trials) or type 2 diabetes not treated by insulin (1 trial). Corrected for study effects, the magnitude of differences in postprandial glucose and insulin responses between the 2 conditions was significantly exacerbated with poorer baseline levels of fasting glucose, insulin and/or surrogate markers of β‐cell function and insulin resistance. This suggests that those with higher underlying levels of insulin resistance may derive greater metabolic benefits from regularly interrupting prolonged sitting than their healthier counterparts. If these findings can be replicated, they may have implications for future targeting and optimization of physical activity/sedentary behaviour interventions in the prevention and management of type 2 diabetes.

Prolonged uninterrupted sitting increases fatigue in type 2 diabetes

Fatigue is a prevalent, costly and disabling clinical complaint among those with type 2 diabetes. In a randomized crossover trial, prolonged uninterrupted sitting increased fatigue by 29% relative to days when sitting was regularly interrupted by brief activity-breaks. This may have implications for diabetes-related quality of life, occupational productivity and self-care.