Epidemiological studies report that elevated postprandial blood glucose is an independent predictor for developing metabolic complications such as cardiovascular disease, type II diabetes mellitus, and obesity (Bonora et al., 2001). In fact, for people without overt diabetes, post-prandial glucose has a stronger association with disease risk than HBA1C (Blaak et al., 2012). This relationship is continuous and lower postprandial glucose levels are beneficial irrespective of threshold values (Levitan et al., 2004). Decreasing hyperglycemia following meal consumption can therefore be a beneficial strategy for reducing the risk of disease for diabetic, prediabetic, and apparently heathy individuals (Blaak et al., 2012; Ceriello et al., 2008; Leiter et al., 2005).
Regular exercise is a standard recommendation as a means to manage blood glucose including post-prandial blood glucose responses (American College of Sports Medicine, 2014) and there is a continuing pursuit to find the minimum exercise necessary to improve cardiometabolic disease risk (Murtagh et al., 2005). For example, glucose uptake into the skeletal muscle can be stimulated through single, acute bouts of exercise via translocation and activation of GLUT4 to the muscle membrane. Beneficial effects of single bout exercise on postprandial glucose responses extend to low effort modalities such as light to moderate intensity walking (59-67% HRpeak) and standing (Aadland and H0stmark, 2008; Nygaard et al., 2009, Lunde et al., 2012; Thorp et al., 2014). However, due to the level of intensity, these forms of exercise require substantial time commitments of at least 20-30 minutes or repeated bouts (Benatti et al., 2017; Bhammar et al., 2017; Murtagh et al., 2005).
Long duration or repeated bouts may be difficult for people to achieve as it can become disruptive to busy lifestyles or unsuitable to many situations (e.g. meetings, presentations, or interviews). High intensity exercise can be of much shorter duration and still elicit beneficial effects on postprandial blood glucose (Adams, 2013; Gillen et al., 2012), however this is mostly unsuitable to conditions outside of controlled laboratory environments. A simple (for those individuals without orthopedic conditions making stairs stepping complex), low cost, and ubiquitously available alternative is stair climbing/descending (at 80-115 stairs/minute) for which repeated bouts are effective in reducing post-prandial blood glucose for people with type 2 diabetes (Honda et al., 2017; Takaishi and Hayashi, 2017). One study reports on a single, short (6 min) stair stepping bout (at 80-110 stairs/min) of moderate intensity which can elicit significant reductions in postprandial blood glucose for men with impaired glucose tolerance (Takaishi et al., 2011). However, whether these effects extend to pre-diabetic individuals, shorter bouts, or women is currently unknown. In addition, there are currently no data on the actual metabolic cost of these types of single stair climbing bouts.
The purpose of the present study was to investigate whether a single, simple to perform activity (for those individuals without orthopedic conditions making stairs stepping complex) such as stair climbing/descending at a self-selected moderate pace of short durations can significantly lower postprandial blood glucose responses compared to a negative control. The secondary aim was to describe the exercise intensity and metabolic cost of the stair climbing/descending bouts. We hypothesized that stair climbing would reduce postprandial blood glucose over time in a dose dependent manner related to metabolic cost.
Thirty adult participants (males n = 20 male, females n = 10; age 26 (5); Table 1) with finger stick fasting blood glucose values in the prediabetes range (i.e. 100-126 mg/dL) were enrolled for the study. All participants were considered low risk for exercise participation per the American College of Sports Medicine (Riebe et al., 2015). Prior to the study, participants were asked to complete the Physical Activity Readiness Questionnaire to screen for potential cardiovascular risks. Participants not within this range were dismissed from the study. All participants provided written informed consent and the study was approved by the Institutional Review Board at San Diego State University.
In this randomized controlled trial with crossover design, participants reported to the laboratory for a total of 5 visits. The first visit was to determine peak aerobic capacity (V[O.sub.2peak]) using a graded exercise test to volitional fatigue. During the second visit, an OGTT was performed. All remaining visits consisted of an OGTT following 1, 3, or 10 minutes of self-selected moderate intensity stair climbing/descending (Figure 1). For all OGTTs participants were asked to fast overnight for a minimum of ten hours, with water allowed ad libitum. For stair climbing/descending trials randomization was accomplished by participants drawing numbers from a concealed container. Prior to the first stair trial, participants were asked to determine a self-selected moderate stepping pace between 90 and 110 steps per minute that they could comfortably maintain for ten minutes. This pace was set to a metronome and held constant across all trials. The stair climbing bouts began at 18, 25, or 27 minutes after finishing the glucose solution for the 10, 3, and 1-minute climbs, respectively, all ending at 28 min post meal consumption. The stair climbing/ descending exercise was completed in a stairwell consisting of 21 steps that were ascended and descended continuously. All visits were 24 hours to one week apart, conducted at the same time of day and the participants were asked to maintain the same diet and exercise habits 48 hours before each trial. The study took place from October 2016 through August 2017.
Peak oxygen consumption (V[O.sub.2peak])
V[O.sub.2peak] values were determined using a treadmill ramp test. Stage 1 of the test consisted of a warm up on the treadmill beginning at 3.5 mph and 1% grade for 3 minutes. During the second stage, speed was increased to 4 mph with a 2% grade for 1 minute. Speed and grade were then increased by 1 mph and 1% grade...