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APPLIED SCIENCES

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

RAFIEI, HOSSEIN1; OMIDIAN, KOSAR2; MYETTE-CÔTÉ, ÉTIENNE1; LITTLE, JONATHAN PETER1

Author Information
Medicine & Science in Sports & Exercise: January 2021 - Volume 53 - Issue 1 - p 150-158
doi: 10.1249/MSS.0000000000002431

Abstract

Representing the lowest end of the physical activity spectrum, sedentary behavior is formally defined as any waking behavior with an energy expenditure of ≤1.5 metabolic equivalents during sitting or reclining posture (1). Sedentary behavior is associated with impaired metabolism and increased cardiometabolic-related morbidity and mortality (reviewed in reference 2). Sedentary lifestyle is a known risk factor for comorbidities and mortality irrespective of physical activity level (3). In young healthy people, sedentary behaviors have been shown to cause a substantial increase in the amount of insulin required to clear infused glucose (4). Postprandial glucose (5), insulin (6), and triglycerides (TG) (7) are linked to risk of cardiovascular disease (CVD) morbidity and mortality. Such evidence warrants investigating novel interventions for interrupting prolonged sitting and targeting postprandial insulinemic, glycemic, and lipidemic responses that could decrease CVD risk. Studies report that reducing sedentary time and breaking up prolonged sitting improve markers of cardiometabolic health (reviewed in reference 8). For example, breaking up prolonged sitting every 20–30 min with 2- to 5-min light-moderate walks (9,10) decreases postprandial glycemia and insulin. The health benefits of such interventions are particularly attractive for individuals who are overweight or obese who often display insulin resistance and are at higher risk of developing type 2 diabetes (T2D) (11).

Accumulating evidence suggests that vigorous-intensity exercise may be particularly effective to promote health by improving cardiorespiratory fitness (12), increasing fat loss, and reducing cardiometabolic risk (13). Low-volume sprint interval training, involving repeated short (10–30 s) “all-out” exercise bouts interspersed by periods of recovery, is often regarded as the most time-efficient alternative for traditional endurance exercise (14,15). Studies report that as few as two to three, 20-s cycling sprints performed as part of a 10-min workout, three times a week over 6–12 wk, can improve fitness, insulin sensitivity, and glucose control (16,17). Recently, the concept of “sprint snacks” —whereby brief isolated bursts of exercise lasting ~20 s are performed with hours of rest in between—has emerged. Sprint snacks performed as three individual 20-s cycling sprints (18) or ~20-s stair climbing efforts (19) with 1- to 4-h rest in between has been shown to be effective at increasing cardiorespiratory fitness in inactive adults. Whether breaking up prolonged sitting with sprint exercise snacks can improve postprandial metabolism and reduce markers of cardiometabolic disease risk is unknown.

Given the metabolic benefits of breaking up prolonged sitting with short activity breaks (9,10) and the potential fitness benefits of sprint snacks (18,19), this study was designed to determine if breaking up prolonged sitting with short (15–30 s) stair climbing exercise “snacks” could improve postprandial metabolic control across the day. If efficacious, this type of intervention could be an attractive strategy to negate the acute detrimental effects of sedentary behavior while improving fitness. To this end, we conducted two separate studies with a randomized crossover design in which young healthy weight men (study 1) or adults with overweight/obesity (study 2) remained sedentary for 9 h while consuming three identical meals, or interrupted this sedentary period with 15- to 30-s stair climbing “snacks” every hour. High-glycemic index meals were provided to study participants given that such diet is commonly consumed in Western society and has been associated with increased risk of obesity, T2D, and CVD (20). We hypothesized that, when compared with a 9-h period of being sedentary, breaking up prolonged sitting with hourly short stair climbing snacks would lower postprandial glucose and insulin responses and reduce free fatty acid levels across the day. Given that breaking up prolonged sitting with light- or moderate-intensity activity seems to benefit metabolism across a range of populations by improving insulin sensitivity (10,21), insulin area under the curve (AUC; a proxy for insulin sensitivity) was chosen as the primary outcome.

METHODS

Study design

A randomized crossover design was used involving two 9-h experimental trials: i) sedentary (SED; participants were sitting on a chair throughout the experimental trial and asked to minimize their movement) and ii) stair “snacks” (SS; ascending three flights of stairs at a brisk speed (15–30 s) once every hour (×8)) with identical meals. A third condition (sedentary low carbohydrate) was also included in the randomization schedule because the original study was designed and funded to measure saliva insulin responses across the day, and a low-insulin response comparator condition was deemed necessary for this research question. The study was registered with three conditions in the clinical trial registry, but because the low-carbohydrate condition was not included in the hypothesis tested herein, only data from the two relevant SED and SS conditions are reported. The exact same high-glycemic index meals of a peanut butter jam sandwich with 400 mL of orange juice from concentrate (~530 kcal; 97 g carbohydrate, 11 g protein, 11 g fat) were provided for breakfast, lunch, and dinner in each condition. Meals in both conditions were matched for calories and were provided at 0, 180, and 360 min. A wash-out period of 3–7 d was chosen to eliminate any potential carryover effects. The study was approved by the University of British Columbia Clinical Research Ethics Board (ID H17-01747) and was registered on ClinicalTrials.gov (NCT03374436). The study conformed to the standards set by the Declaration of Helsinki. All participants provided written informed consent before data collection.

Participants

Participants were recruited through distribution of posters, by e-mail, and by word of mouth on the University of British Columbia campus (Kelowna, British Columbia, Canada). The main objectives were to determine the effects of stair snacks in young healthy-weight (HW) men (n = 12; age, 22.8 ± 4.3 yr; body mass index (BMI), 24.3 ± 2 kg·m−2; study 1) and in adults with overweight/obesity (OW; n = 11, characterized with elevated waist circumference >88 cm for women and >102 cm for men; age, 50.2 ± 14.3 yr; BMI, 35.1 ± 6.4 kg·m−2; study 2). Study 1 was designed as a pilot test of stair climbing snacks and included only male participants to minimize the potential influence of menstrual cycle on insulin sensitivity and glucose tolerance. Based on the successful feasibility of performing eight stair climbing snacks across 9 h, study 2 began after study 1 was completed and included both male and female participants, which facilitated easier recruitment of participants with overweight/obesity characterized with elevated waist circumference and to be inclusive of both sexes. Inclusion criteria for study 1 were as follows: 1) BMI of 18.5–24.9 kg·m−2 and 2) age of 18–35 yr. Inclusion criteria for study 2 were as follows: 1) waist circumference ≥88 cm for women or ≥102 cm for men (elevated waist circumference in our study was defined according to World Health Organization classification of the waist circumference cutoff points made for overweight or obesity, and association with disease risk) and 2) age of 18–69 yr. Exclusion criteria for both studies were as follows: 1) previous diagnosis of diabetes; 2) currently taking insulin, oral hypoglycemic drugs, or any medications affecting blood glucose; 3) diagnosed CVDs; 4) current smoker; 5) allergy to eggs or peanuts; 6) undertaking serious (>5 d·wk−1) exercise training; 7) medical/orthopedic conditions that would limit physical activity; and 8) individuals following a special diet such as ketogenic diet or being vegan. Among female participants in study 2, five were postmenopausal and three were premenopausal (two with intrauterine device and one on birth control pills). Premenopausal female participants were tested in the follicular phase of the menstrual cycle (days 3–9 after menstruation).

Baseline testing

On the first visit, participants provided written informed consent and were interviewed by a registered dietician to collect data about lifestyle habits and medical conditions to confirm eligibility. Then, anthropometric measurements (height, weight, waist circumference, and hip circumference) were measured. Waist circumference and hip circumference were measured in duplicate to the nearest 0.5 cm using standard procedures.

Standardization of diet and activity before study

Before experimental trials, participants were interviewed by a study dietician to confirm they were not on a specific diet (e.g., vegan, keto, etc.) and had not lost or gained weight recently. Energy intake for the day before each trial was controlled by asking the participants to fill out a 24-h food recall a day before visit 1 and instructing them to reproduce the exact same diet on the day before subsequent testing days. This was confirmed by a dietician in the morning before running each trial. We did not specifically prescribe energy intake on the day before the trial in order to increase external validity and reduce participant burden, but each participant ate the same foods (type and quantities) before each trial, which was guided and verified by the study dietician. Energy intake on the day of the trial was not adjusted between SS and SED, as the energy expenditure during the short (~15–30 s) stair climbing was, by design, very low and it would not have been difficult or impractical to accurately determine the energy expended by the stair climbing exercise in the protocol. Participants were instructed to abstain from alcohol and refrain from exercising on the day before each experimental trial visit, which was confirmed by self-report and by measuring steps taken using an activity tracker (Mio Slice watch, Canada). Steps recorded were only available in the HW group because of technical issues with the watch in the OW group. Self-reported sleep hours on the night before each visit were also recorded. Compliance with activity standardization, confirmation of sleep hours, and dietary control were confirmed by the dietician upon arrival to the laboratory for each experimental visit.

Experimental trials

Participants arrived at the laboratory between 7:00 and 8:30 am after an overnight fast (≥10 h). An intravenous catheter (BD Nexiva; Becton Dickinson, Franklin Lakes, NJ) was inserted into an antecubital vein for repeat blood sampling. Samples were drawn into tubes containing ethylenediamine tetraacetic acid (EDTA-K2) at time 0 (fasting) and every 30 min for a total 19 blood samples across 540 min. Samples were immediately centrifuged at 1550g for 15 min at 4°C and kept in −80°C freezer before batch analyses (details hereinafter). In all trials, participants remained seated in a chair for 9 h working on a computer, watching TV, or reading. Participants were allowed to walk (~10 m) from the laboratory to use the bathroom. Meals were provided just after the first morning blood sample (time 0) and at 180 and 360 min. Water was provided ad libitum. The aforementioned wrist watch monitor was used to track steps and heart rate over the 9-h laboratory visit. In the SS condition, participants walked (~25 m) to a stairwell adjacent to the laboratory and were instructed to ascend three flights of stairs without skipping steps (55 steps) as quickly and safely as possible, every hour beginning at 60 min, for a total of eight stair snacks. The stair climbing snacks at 180 and 360 min were performed immediately before meal consumption. Participants with OW were asked to climb the stairs at a self-selected challenging pace given that stair climbing at a sprint pace was not feasible for some participants. Stair climbing was supervised by a research technician who recorded RPE (category-ratio 0–10 scale), total time of each stair climb, and heart rate immediately after each stair snack. Details of the experimental protocol are presented in Figure 1.

FIGURE 1
FIGURE 1:
Overview of the study design. Meal, high-glycemic index meal.

Randomization

Participants were randomized to complete the intervention trials using a Williams latin square design and an online randomizer (https://statpages.info/latinsq).

Biochemical analyses

Blood metabolites were analyzed using commercially available kits as follows: plasma glucose (glucose hexokinase; Pointe Scientific Inc., Canton, MI), plasma nonesterified fatty acids (NEFA; HR Series; Wako Diagnostics, Mountain View, CA), and plasma TG (Pointe Scientific Inc., Canton, MI) were analyzed on a Chemwell 2910 automated analyzer (Awareness Technologies, Palm City, FL). Plasma insulin (human insulin enzyme-linked immunosorbent assay; Crystal Chem, Elk Grove Village, IL) was analyzed on an iMark Microplate absorbance reader (Bio-Rad, Hercules, CA). All assays except TG were run in duplicate following the manufacturer’s instructions. Intra-assay coefficients or variance averaged 3.2% for plasma glucose, 5.9% for plasma insulin, and 3.3% for NEFA.

Statistical analyses

All values are reported as the mean (SD). The study was designed as a pilot study aiming to enroll 12 participants in each group. Sample size calculations were performed for the primary outcome of insulin AUC based on previous studies reporting 15%–20% reductions in postprandial insulin in activity break versus sedentary conditions (10,22) yielding effect sizes of d = 1.0. With a conservative correlation of r = 0.5 between repeated measures, a two-tailed α of 0.05, and power of 0.80, it was estimated that 10 participants would be required to detect a significant difference in the primary outcome. The total (9 h) AUC for plasma insulin, glucose, NEFA, and TG were calculated according to the trapezoid method using baseline of zero (Prism version 8.0; GraphPad Software Inc.). The positive incremental AUC was calculated using the trapezoid rule with baseline subtraction. AUCs in SED versus SS condition were analyzed using t-test and reported as main analyses. The main analyses for insulin and glucose were supplemented with a linear mixed-effects model with fixed repeated-measures effects of meal (breakfast, lunch, dinner), condition, and their interaction and a random effect of participants to explore the difference between 3-h AUC for each meal. Significant interactions between meal and condition were followed up with pairwise comparisons examining each meal between conditions, whereas a main effect of meal was followed up with pairwise comparisons using Bonferroni adjustments with conditions collapsed. Because the two studies were run at different times and the HW group included only male participants, the two groups were analyzed in separate models. Before all statistical testing, normality and skewness were assessed by Q–Q plots and data were natural log transformed when required. Cohen d effect sizes were calculated for pairwise comparisons using the method that was previously defined for repeated measures (23). In this method, mean and SD of the pairwise groups and their correlation were taken into account. Significance was set at P < 0.05.

RESULTS

Baseline characteristics of participants are presented in Table 1. All participants complied with the 24-h dietary replication and refrained from physical activity aside from activities of daily living before each trial. There were no differences in steps for 24 h before each trial in the HW group (P = 0.86) and no differences in hours of sleep on the night before each trial in each group (P = 0.10 and P = 0.69, HW and OW, respectively; Table, Supplemental Digital Content 1, Characteristics of the participants for the day before each trial, http://links.lww.com/MSS/C38). Characteristics of the stair climbing snacks for each group are presented in Table 2. As expected, HW participants ascended the three flights of stairs quicker (range, 13.4–19.7 s) on average when compared with participants with OW (range, 18.3–60.0 s).

TABLE 1 - Baseline characteristics of study participants.
Characteristic HW OW
No. participants (M/F) 12 (12/0) 11 (3/8)
Age, yr 22.8 (4.3) 50.2 (14.3)
Weight, kg 75 (5.7) 101.2 (19)
Body mass index, kg·m−2 24.3 (2) 35.1 (6.4)
Waist circumference, cm 80.2 (4.6) 108.7 (15.1)
Hip circumference, cm 99.9 (4.1) 121.5 (12.1)
Waist-to-hip ratio 0.80 (0.03) 0.89 (0.07)
Resting heart rate, bpm 61 (12) 69 (11)
Fasting insulin, pmol·L−1 28.9 (8.9) 37.1 (12.5)
HOMA-IR 1.05 (0.33) 1.54 (0.60)
Fasting glucose, mmol·L−1 4.9 (0.3) 5.4 (0.5)
Fasting NEFA, mmol·L−1 0.32 (0.08) 0.46 (0.9)
Fasting TG, mmol·L−1 0.95 (0.38) 1.34 (0.63)
Values are presented as mean (SD).
HOMA-IR, homeostatic model assessment of insulin resistance; M/F, male/female.

TABLE 2 - Characteristics of the stair climbing snacks for each group.
HW OW
Characteristic SED SS SED SS
Steps day of trial 100 (90) 951 (358)* 407 (536) 853 (297)
Mean RPE for stair snacks 4.6 (2.3) 4.1 (2.3)
Mean HR for stair snacks 102 (17) 109 (23)
Mean stair climbing time 15.6 (1.3) 29.4 (11.9)
Values are presented as mean (SD).
*Significant vs SED within the group.

AUC

Insulin, glucose, and NEFA over time and total AUCs in participants with HW and OW are presented in Figures 2–4. Positive incremental AUC analyses resulted in the same general conclusions and are presented in Supplemental Figure 1 (Figure, Supplemental Digital Content 2, Incremental AUC analyses in young healthy weight men (left) or adults with overweight/obesity (right), http://links.lww.com/MSS/C39).

FIGURE 2
FIGURE 2:
Insulin over time and total AUC in the HW (top) or OW (bottom) group. Nine-hour insulin over time and total AUC in the HW (A, B) or OW (C, D) group. Participants were sedentary for 9 h with three identical meals (SED) or performed 15–30 s of stair climbing “snacks” every hour (SS), with the same meals provided at 0, 180, and 360 min. *P < 0.05; t-test was used to compare AUCs between the conditions within each group.
FIGURE 3
FIGURE 3:
Plasma glucose over time and total AUC in the HW (top) or OW (bottom) group. Nine-hour glucose over time and total AUC in the HW (A, B) or OW (C, D) group. Participants were sedentary for 9 h with three identical meals (SED) or performed 15–30 s of stair climbing “snacks” every hour (SS), with the same meals provided at 0, 180, and 360 min.
FIGURE 4
FIGURE 4:
Plasma NEFA over time and total AUC in the HW (top) or OW (bottom) group. Nine-hour plasma NEFA over time and total AUC in the HW (A, B) or OW (C, D) group. Participants were sedentary for 9 h with three identical meals (SED) or performed 15–30 s of stair climbing “snacks” every hour (SS), with the same meals provided at 0, 180, and 360 min. *P < 0.05; t-test was used to compare AUCs between the conditions within each group.

Total Insulin AUC

STUDY 1 (HW)

No significant difference between SS and SED for total insulin AUC was observed (−17.4%, P = 0.24, d = 0.4; Figs. 2A, and B).

Study 2 (OW)

In participants with OW, a significantly lower total insulin AUC was found in SS versus SED (−16.5%, P = 0.036, d = 0.94; Figs. 2C, and 2D).

Total glucose AUC

STUDY 1 (HW)

No difference was observed for total glucose AUC between SED and SS in HW participants (P = 0.17, d = 0.48; Figs. 3A and 3B).

STUDY 2 (OW)

In participants with OW, no significant difference for total glucose AUC between SS and SED was observed (P = 0.31, d = 0.34; Figs. 3C and 3D).

Total NEFA AUC

STUDY 1 (HW)

In HW participants, no difference between SS and SED for total NEFA AUC was found (−9%, P = 0.22, d = 0.4; Figs. 4A and 3B).

STUDY 2 (OW)

In participants with OW, a significantly lower total NEFA AUC was found in SS versus SED (−21%, P = 0.016, d = 1.2; Figs. 4C and 3D).

Total TG AUC

STUDY 1 (HW)

No difference was found for total TG AUC between SS and SED (P = 0.72) in HW participants (Table, Supplemental Digital Content 3, AUC analyses for plasma TG, http://links.lww.com/MSS/C40).

STUDY 2 (OW)

In participants with OW, no significant difference was detected for total TG AUC between SS and SED (P = 0.67; Table, Supplemental Digital Content 3, AUC analyses for plasma TG, http://links.lww.com/MSS/C40).

The primary analyses were supported by the linear mixed-effects model showing a main effect of condition for insulin (P = 0.033) in adults with OW. The meal–condition interaction was not statistically significant (P = 0.31), but there was a main effect of meal (P = 0.002) for 3-h insulin AUC. In adults with OW, pairwise comparisons revealed that 3-h postlunch and postdinner insulin AUCs were lower than 3-h postbreakfast AUC (−22% [P < 0.0001] and −26% [P = 0.0006], respectively). There were no significant main effects of condition (P = 0.65), meal (P = 0.48), or their interaction (P = 0.65) in participants with OW for 3-h postmeal glucose AUC. Main effects of meal were observed for insulin (P < 0.0001) and glucose (P = 0.028) in HW individuals, but there were no main effects of condition (insulin: P = 0.24; glucose: P = 0.18) or meal–condition interactions (insulin: P = 0.72; glucose: P = 0.23). In HW participants, 3-h postlunch and postdinner insulin AUCs were lower than 3-h postbreakfast AUC (−36% [P < 0.0001] and −32% [P < 0.0001], respectively). Also, in HW participants, 3-h postbreakfast glucose AUC was lower compared with postdinner AUC (−5.4%, P = 0.023).

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.

CONCLUSIONS

Overall, the current findings demonstrate that interrupting prolonged sitting with brief hourly bouts of stair climbing may help to negate some of the detrimental metabolic effects of sedentary behavior in individuals with overweight/obesity. Although it is unlikely that this type of activity can replicate all the benefits of more sustained exercise bouts, individuals with overweight/obesity, who are at elevated risk of T2D and CVD, may benefit from incorporating brief daily stair climbing exercise “snacks” that could be performed at home, workplace, or school (e.g., during coffee or washroom breaks). Our results, combined with the fact that stair snacks have been shown to improve cardiorespiratory fitness (19), suggest that this novel exercise approach warrants further investigation, particularly in real-world settings. The findings of study 1 are likely generalizable to young healthy men, and those of study 2 are likely generalizable to middle-age individuals with overweight/obesity. Our findings are based on the acute context, and hence, longer-term studies will need to be conducted to investigate the feasibility and efficacy of such brief intense physical activities in the real-world settings.

H. R. was supported by a Mitacs Accelerate Fellowship (No. IT09918). Additional funding for the study was provided by a Natural Sciences and Engineering Research Council Discovery Grant to J. P. L. (grant no. 435807). J. P. L. is supported by a Canadian Institutes of Health Research New Investigator Salary Award (MSH-141980) and a Michael Smith Foundation for Health Research Scholar Award (16890).

J. P. L. holds shares in Metabolic Insights Inc., a for-profit company that is developing noninvasive metabolic monitoring tools. H. R., K. O., and É. M. -C. declare that they have no conflicts of interest relevant to the content of this article.

The data sets generated and analyzed during the current study are available from the corresponding author on reasonable request.

J. L. and H. R. designed the trial. H. R. collected the data with support from K. O. and E. M. C. H. R. and J. L. planned and conducted the statistical analysis, and H. R. wrote the first draft of the manuscript under the supervision of J. L. All authors reviewed and revised the manuscript and approved the final version.

The authors would like to thank the participants for their time and dedication to the study. They also acknowledge the assistance of Ms. Courtney Chang with blood sample collection and processing. They also would like to thank Dr. Martin Gibala for his valuable insight on the article. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

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Keywords:

STAIR CLIMBING; BRIEF INTENSE EXERCISE; POSTPRANDIAL METABOLISM; INSULIN RESISTANCE; INTERVAL TRAINING; INTERMITTENT EXERCISE

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