Metabolic Effect of Breaking Up Prolonged Sitting With Stair Climbing Exercise Snacks

Hossein Rafiei; Kosar Omidian; Étienne Myette-Côté; Jonathan Peter Little

Disclosures

Med Sci Sports Exerc. 2021;53(1):150-158. 

In This Article

Discussion

Stair Snacks and Postprandial Insulin Responses

The main novel finding of this study was that breaking up 9 h of prolonged sitting with brief vigorous stair climbing exercise "snacks" lowered insulin across the day in participants with overweight/obesity. This evidence of lowering postprandial insulin responses with such a small overall dose of exercise could be important for reducing the detrimental cardiometabolic effects of sitting, as postprandial insulin is an independent predictor of CVD morbidity and mortality.[6] In this study, we have adapted previously used protocols for breaking up sedentary time (typically 2–5 min of walking) with shorter higher-intensity stair climbing exercise "snacks" that require minimal time commitment.[10,21]

Whereas stair climbing lowered postprandial insulin responses in participants with OW who likely had greater insulin resistance and experienced more pronounced insulin spikes in response to the high-glycemic index meals, it did not lower insulin responses in HW male participants. In agreement with this, some studies have shown that stair climbing had no favorable effects on attenuating glucose or insulin levels or improving insulin sensitivity assessed by an oral glucose tolerance test in healthy participants.[24] The lack of an improvement in insulin AUC in HW participants (study 1) could be the result of multiple factors. For example, it has been suggested that healthy, insulin-sensitive individuals have limited capacity to respond to short bouts of activity because of the exercise being of too low intensity/volume, relatively good baseline glycemic and insulin control, and as in our study, higher baseline physical activity levels (reviewed in Reference.[25] Because the participants of the two studies herein were not age and sex matched, we did not intend to statistically compare the results between participants with HW and OW. It is also possible that the activation of sympathetic nervous system and release of counterregulatory hormones after stair climbing could have increased hepatic glucose production and blunted any insulin-lowering effects in HW participants, who did the stair climbing snacks faster than did participants with OW. Higher energy expenditure of stair climbing in participants with OW (because of higher body mass) could be another potential mechanism of improved postprandial metabolic profile. Taken together, our finding suggests that even short bouts of relatively intense exercise performed as stair climbing may improve insulin sensitivity in adults with overweight/obesity.

Postprandial Glycemia

Postprandial hyperglycemia is a risk factor for CVD not only in T2D patients but also in healthy individuals.[26] Limiting postprandial glucose spikes is therefore considered an optimal approach for metabolic health. Our study showed that breaking up prolonged sitting with stair climbing snacks did not improve postprandial glucose AUC in participants with HW or OW. There are conflicting results on the effectiveness of short intense exercise bouts in reducing postprandial glycemia. Some studies have shown that breaking up prolonged sitting with frequent short bouts of activity could be an effective strategy to reduce postprandial hyperglycemia.[10,21] In one example, it has been shown that stair climbing–descending exercise (3-min bout at 60 and 120 min after the meal) decreased postprandial glucose compared with 3 h of sitting in patients with T2D.[27] Similarly, other studies have also shown favorable effects of bouts of stair ascending–descending exercise on postprandial hyperglycemia in individuals with prediabetes and diabetes[28] or middle-age sedentary men with impaired glucose tolerance.[29] In contrast, Godkin et al.[30] found unchanged blood glucose after an acute session of 60-s bouts of vigorously ascending and slowly descending a flight of stairs and after 18 sessions over 6 wk in people with T2D. Also, unaltered postprandial glycemia has been reported after breaking up prolonged sitting (2.5 h) with other types of activity breaks (2-min bouts of walking every 20 min) in young normal-weight men and women.[31] These conflicting findings could be due to different study designs including health status and age of participants, and duration, frequency, and intensity of stair climbing exercise, among other determinants. Although the optimal exercise strategy (dose, duration, timing) for improving postprandial glycemia is not known, a recent systematic review that included a total of 42 studies concluded that physical activity breaks were slightly more effective than one continuous bout of physical activity for glycemic attenuation when experimental conditions were energy expenditure matched.[32]

After acute exercise and chronic training in participants without diabetes, it is common to see an increase in insulin-stimulated glucose uptake (insulin sensitivity) coupled with a decrease in glucose-stimulated insulin secretion, such that glucose disposition is unchanged. This is likely another rationale for the lack of any apparent effect of stair climbing exercise on postprandial plasma glucose AUC. The timing of stair climbing snacks in our study (immediately before and then 60 min after each meal) may have also contributed to the unaltered plasma glucose because it was suggested that physical activity bouts immediately after a meal might be more effective than physical activity immediately before or 30 min after a meal.[33] Our results suggest that acute short bouts of relatively intense exercise performed as stair climbing may not be sufficient to reduce postprandial hyperglycemia in participants with HW or OW.

The Effects on Postprandial Lipid Profiles

Persistent high plasma NEFA concentration is shown to interfere with insulin signaling leading to liver and skeletal muscle insulin resistance (reviewed in Reference.[34] Similarly, persistent postprandial hypertriglyceridemia has been linked to elevated oxidative stress, inflammation, endothelial dysfunction, and CVD risk.[35] Accordingly, decreasing postprandial exposure to NEFA and TG using exercise is hypothesized to reduce CVD risk. In our study, breaking up prolonged sitting with stair climbing exercise snacks lowered postprandial plasma NEFA AUC in participants with OW but not HW. The decrease in NEFA concentration across the day could be one underlying mechanism for increased indicators of insulin sensitivity seen in participants with OW.[36] In contrast to NEFA, we observed no effects of SS on TG in participants with HW or OW. It was shown that short-term stair ascending–descending exercise[27] or interrupting prolonged sitting with brief bouts of light walking[37] did not attenuate postprandial NEFA or TG in individuals with T2D. Similar to our findings, breaking up 9-h prolonged sitting with 1-min 40-s walking every 30 min did not alter TG responses in healthy, normal-weight participants.[21] A meta-analysis including 20 studies that looked at the effect of interrupting prolonged sitting with light- to moderate-intensity physical activity concluded that regular activity breaks decreased postprandial glucose and insulin, but that reduction in postprandial TG was only observed 12–16 h after intervention.[2] Thus, it is possible that the effect of exercise on postprandial TG is delayed, which seems related to the parallel increase in lipoprotein lipase activity that peaks 8–16 h after a bout of exercise.[38] Breaking up prolonged sitting with stair snacks seems sufficient to lower exposure to NEFA in adults with OW, which could contribute to improved insulin sensitivity, but this novel intervention did not seem to affect postprandial TG.

Feasibility and Application of Stair Climbing "Snacks"

Studies have previously demonstrated that low-volume HIIT and stair climbing are well tolerated in participants with T2D.[39] In line with other studies,[40] RPE score from our study suggests that stair climbing was well tolerated by participants and could potentially be implemented in daily life and at workplace to overcome barriers for physical activity, such as lack of time and access to indoor exercise facilities.[41] Our stair climbing protocol involved ascending three flights of stairs as quickly and safely as possible; it has, however, been suggested that bouts of stair ascending–descending using a short flight of stairs could be a more feasible strategy for many people, particularly unfit elderly individuals.[42] Although the stair climbing snacks were effective in improving postprandial insulin and NEFA responses in participants with OW, this does not suggest that individuals could achieve all the health benefits of long-term physical activity of longer durations. We suggest that at workplaces where employees have to sit for a long time, strategies encouraging individuals to regularly interrupt their prolonged sitting behavior with brief activity breaks, including brief stair climbing exercise, may have metabolic benefits. Whether and how to efficiently implement such strategies or policies at the workplace or in the community warrant further investigation.

Strengths and Limitations

The randomized crossover design, prolonged (9 h) time frame for this type of study, frequent blood sampling across the trials, and use of real-life mixed meals are all strengths of this research, but the study is not without limitations. The small sample size may have reduced our ability to detect statistically significant changes, particularly in HW participants. We report effect sizes to help the reader gauge the effect of each condition on all variables. Another limitation is that only young men were recruited for study 1, which precluded direct statistical comparisons of the postprandial responses with the participants in study 2, who were not sex or age matched. It has recently been shown that sex can affect the metabolic responses to breaking up prolonged sitting with activity breaks, likely because of hormonal changes and menopausal status.[37] Most women (n = 5) in study 2 were postmenopausal and the remaining (n = 3) completed the trials during the follicular phase so the comparisons within participants were valid, but our study is underpowered to explore sex differences. Another limitation is that the metabolic effects of stair climbing snacks were studied acutely across a single day, and therefore, it is not known whether there would be any possible long-term benefits on CVD risk with this approach.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....