Disrupting Sedentariness With Short Exercise Bouts Improves Insulin/Glucose Metabolism

You don’t have to see the whole staircase, just take the first step. Martin Luther King, Jr.

By Tobias Engeroff, Eszter Füzeki, Lutz Vogt, and Winfried Banzer; Han C. G. Kemper, Academic Editor

The health consequences of prolonged sedentary behavior—defined as activities with ≤1.5 metabolic equivalents of energy expenditure in a sitting or reclining posture—include an increased risk for cardiometabolic diseases and all-cause mortality; it has also been suggested to negatively affect mood and well-being. Fitness and exercise may counteract the detrimental metabolic and mood adaptations during prolonged sitting. Interrupting sitting with short exercise bouts could be a further option to limit the negative effects of sedentariness in settings which do not allow replacement or reduction of sitting time. Multiple meta-analyses of randomized controlled trials (RCTs) consistently confirmed the beneficial effect of exercise on markers for glucose and fat metabolism during sedentary behavior.

This study distinguishes the immediate effects of a single bout vs. work-load and intensity-matched repeated exercise breaks on subjective well-being, blood glucose, and insulin response during sedentary time; and assesses the influence of fitness and caloric intake on metabolic alterations during sedentariness

Methods & Results

Based on contradictory results concerning the non-inferiority of a single bout of exercise, the specific objective of this study was to assess if exercise prior to sitting leads to comparable beneficial effects on well-being, glucose, and insulin metabolism than repeated exercise breaks during sedentary behavior. This study also analyzed the moderating effects of dietary caloric intake and cardiorespiratory fitness on metabolic alterations during sedentary behavior.

Eighteen women underwent cardiopulmonary exercise testing and 3 4-hour sitting interventions: 2 exercise interventions (70% VO2max, 30 min, cycle ergometer: (1) cycling prior to sitting; (2) sitting interrupted by 5 × 6 min cycling, and 1 control condition (sitting). Participants consumed 1 meal—consisting of white toast bread, cheese, and jam—with a caloric value of 1124 kJ/100 g (268.41 kcal/100g), and a macronutrient proportion of 51% carbohydrate, 35% fat, and 14% protein. Participants chose the portion size of their meal during their first intervention, and the portion size was kept constant for the other 2 interventions. The meal ingestion during each of the 3 trials took part immediately before the 4 hours of sitting, and was the first bolus received after an overnight fast. Each subject completed 3 interventions: 1. A single bout of 30 min exercise (70% VO2max cycling on an ergometer) prior to uninterrupted sitting; 2. Sitting interrupted by 5 exercise breaks of 6 min ergometer cycling each (70% VO2max); 3. Uninterrupted sitting without exercise. The interventions were separated by a minimum of 7 days and a maximum of 21 days, and were performed in a balanced (block-randomization of sequence) design. Total sitting time was 4 hours in all 3 trials. Sitting mimicked basic aspects of office work. Participants read, worked, or used the internet on their laptops.

Exercise breaks (4057 ± 2079 μU/mL·min) reduced insulin values compared to a single bout of exercise (5346 ± 5000 μU/mL·min) and the control condition (6037 ± 3571 μU/mL·min) (P ≤ 0.05). ANCOVA revealed moderating effects of caloric intake (519 ± 211 kilocalories) (P ≤ 0.01), but no effects of cardiorespiratory fitness (41.3 ± 4.2 mL/kg/min). Breaks also led to lower depression, but higher arousal compared to a no exercise control (P ≤ 0.05). Both exercise trials led to decreased agitation (P ≤ 0.05). Exercise prior to sitting led to greater peace of mind during sedentary behavior (P ≤ 0.05). Just being fit or exercising prior to sedentary behavior are not feasible to cope with acute detrimental metabolic changes during sedentary behavior. Exercise breaks reduce the insulin response to a meal. Despite their vigorous intensity, breaks are perceived as positive stimulus. Detrimental metabolic changes during sedentary time could also be minimized by limiting caloric intake.

Discussion

This experiment underlines the influence of caloric intake on glucose and insulin spikes during postprandial sedentariness, and also on the insulin-lowering effect of exercise breaks. The sample showed a broad range of cardiorespiratory fitness. However, fitness had neither an impact on detrimental changes in glucose or insulin metabolism during sedentary behavior, nor on the beneficial effect of exercise breaks. Nor did fitness influence acute metabolic changes during prolonged sitting in postprandial state; as such, future studies need to analyze whether body composition or other modifiable factors which are related to fitness influence metabolic reactions during sedentary time.

The data shows that both the insulin response to food intake during sitting and the insulin-lowering effect of exercise breaks are related to the number of calories ingested. Consequently, adjusting the timing or amount of food and beverage intake during sedentary behavior could be an important intervention strategy to mitigate detrimental metabolic effects.

The study findings support the hypothesis that breaks, but not a single exercise bout, can maintain enzymatic function or attenuate degradation of insulin-independent glucose transporters during prolonged sitting.

Neither a single exercise bout prior to sitting nor exercise breaks during sitting led to lower ratings of well-being during sedentary behavior compared to a no-exercise control. Both intervention forms led to lower self-perceived agitation. Continuous exercise in the morning also induced a greater feeling of peace of mind. Breaking sedentariness with vigorous-intensity exercise bouts induced higher arousal and lower levels of depression after 4 hours of sitting. Against anecdotal evidence, these findings indicate that both interventions are perceived as a positive experience when applied in a sedentary setting.

Conclusions

In summary, the study authors showed that in a realistic setting with a meal mimicking a typical western breakfast and a sedentary period of 4 hours (simulating half a workday until lunch break), regular short exercise breaks, but not exercise prior to sitting, can lower blood insulin levels in premenopausal, healthy, female participants. Caloric intake strongly influences metabolic regulation and must be considered when interpreting these and other findings. In this study cohort, cardiorespiratory fitness had no influence on changes of cardiometabolic markers. Direct comparison of participants with high vs. low cardiorespiratory fitness in larger study samples might yield more insight whether, and if yes, to what extent, fitness can protect from the acute negative health effects of sedentary behavior. The results of this study confirm that for good health and good mood, not only staying active according to recommendations, but also breaking up long periods of sitting, is of high relevance. Physically active breaks, even with vigorous intensity, are perceived as a positive influence during prolonged sitting. This study also suggests that limiting food and beverage intake with high carbohydrate content during sedentary behavior might mitigate negative metabolic effects.