Regular stair-climbing exercise has been shown to be effective in improving cardiovascular fitness (6,8,12,13), reducing cholesterol levels (6), decreasing body fat (8), and increasing the strength of the lower limbs (13). In addition, climbing public-access stairs as an exercise mode possesses many other advantages such as convenience, privacy, no specialized equipment, and low cost when compared with other traditional exercises. These reasons should make stair-climbing the one mode of exercise that is attractive to the general public. It can further be argued that the value and promotion of stair-climbing as an exercise mode for the masses is even more relevant to countries like Singapore, a land-scarce island where 86% of its population live in government-built high-rise flats (14).
Exercisers are intuitively concerned about the calories used when exercising. They would like to know whether a particular physical activity is effective in expending the desired amount of calories. Being able to provide accurate estimates of the amount of calories expended during stair climbing would be useful and possibly help to motivate the public to incorporate the use of stairs, at least as an incidental activity to everyday living, if not as a routine exercise for health and weight management (15). Although previous studies have determined the caloric cost of stair climbing, few of them have been conducted on an actual staircase (5,17). Thus, the purpose of the current study is to determine the heart rate and oxygen uptake responses during, and the intensity and caloric cost of, ascending and descending a public-access staircase.
A total of 103 subjects (56 male and 47 female) completed the ascending trial. Part of the data of this ascending trial was used to develop a field-based stair-climb test (21), a convenient and simple self-assessment of fitness. For the descending trial, 49 subjects (24 male and 25 female) were involved. Of this descending cohort, 26 (18 male and 8 female) subjects were from the ascending cohort. The subjects’ physical and laboratory performance data of the different cohorts are summarized in Table 1.
All subjects completed a preparticipation medical questionnaire and clearance before undergoing any experimental procedures. They were briefed on the benefits and potential risks involved and were at liberty to withdraw at any point during the study. All subjects provided informed written consent for the study, which was approved by the ethics committee. Subjects underwent a maximal exercise test on a treadmill to determine their maximum heart rate (HRmax) and maximal oxygen uptake (V̇O2max) in the laboratory before the field measurement. Field measurements were conducted within 3 wk of the laboratory test at a randomly chosen government-built Housing and Development Board (HDB) flat in a local housing estate. All climbing activities were conducted in this block. Subjects ascended to and descended from the 12th floor. The 12th floor (or 11 stories) was decided solely on the basis that this is the average minimum number of floors for a typical HDB flat. The 11 stories consisted of 22 flights of stairs of 180 steps with each step of 15 cm in height, for a total vertical displacement of 27.0 m. Each flight of stairs has eight steps except for the lowest flight, which has 12 steps. The design of the staircase in a typical HDB flat is such that there is a horizontal landing (∼2.0 m square) between each flight of stairs.
Maximal oxygen uptake.
A progressive incremental graded exercise protocol on a treadmill was utilized. Details of the protocol is described elsewhere (21). Expired gases were measured using an open circuit system with portable spirometry (Model K4, Cosmed, Rome, Italy) that had previously been validated (9). The K4 system comprised the analyzer unit, battery pack, and face mask, together with a heart rate monitor (Polar Oy model Sports Tester, Kempere, Finland). The system weighs ∼800 g and was strapped onto a harness that the subject wore over his or her attire. The K4 system analyzer unit was calibrated according to the manufacturer’s instructions before each test. Data were recorded every 15 s, and the highest oxygen and heart rate observed during the test was reported as the individual’s V̇O2max and HRmax. Subjects were considered to have achieved his/her V̇O2max based on attaining two of the following criteria: i) volitional exhaustion, ii) respiratory quotient of > 1.05, and/or iii) reached or exceeded 95% of the individual’s estimated HRmax (based on the formula: 220 − age).
Ascending and descending trials.
The ascent and descent were conducted as separate trials. For subjects involved in both ascent and descent, these were performed during the same field session in a random, counterbalanced order. A compulsory 15 min of quiet sitting was instituted between the ascent and descent trials to ensure subjects returned to baseline levels. Subjects were instructed on the test procedures before the climb. Subjects were instructed to ascend or descend at a brisk, rhythmic, and constant pace. They were to take only a single step at a time and running was not allowed. They were not allowed to stop or use the side-railings for support throughout the climb. Subjects were provided with standardized stretching exercises followed by three practice trials up or down two stories. An investigator accompanied each subject on his or her climb to ensure compliance and noted down the subject’s climb time for ascending (CTascend) and descending (CTdescend), with a stop-watch (model HS-5 Casio, Tokyo, Japan).
For all field trials, subjects were equipped with the K4 spirometry system for measurement of oxygen uptake and heart rate during climbing. The equipment did not hinder or obstruct subjects’ movement or vision. The analyzer was calibrated before each subject’s climb. The oxygen uptake and heart rate measured during the last 30 s (two readings) of the climb trial was averaged and taken as the ascending (i.e., V̇O2ascend and HRascend) and descending (V̇O2descend and HRdescend) responses, respectively. Temperature and humidity were determined every hour and any change was input into the spirometry system analyzer during the subsequent calibration. Temperature and humidity ranged from 26 to 30°C and 68 to 85%, respectively, throughout the study. It is worth noting that there were no serious injuries or medical complications during the conduct of the study.
For the study, the following calculations were made:
i. Gross energy expended for either ascending or descending the 11 stories.
Assuming 5 kcal expended for every L of oxygen consumed (10, pp. 128), the gross energy expended = [mean oxygen uptake (L·min−1) × 5 kcal LO2−1] × duration of climb;
ii. Gross energy cost for either ascending or descending a single step (kcal·step−1) = gross energy expended during ascent or descent divided by 180 steps; and
iii. METs intensity of either ascending or descending is calculated by dividing the mean oxygen uptake (mL·kg−1·min−1) during the climb with 3.5 mL·kg−1·min−1.
The Student unpaired t-test was used to determine whether there were any significant differences between genders in the physical and climbing variables measured as well as between subjects in the ascending and descending trials. The Pearson product moment correlation was used to determine the relationship between oxygen uptake and heart rate with body mass and duration of the climbing trials. The level of significance was set at 0.05. The Statistical Package for Social Sciences (version 10.0 for Windows) was used for all statistical analysis.
In Table 1, for both the ascending and descending trial cohorts, the men were significantly taller, with a higher body mass and V̇O2max, than the women. Women in the ascending trial cohort were significantly older but had a lower absolute and relative V̇O2max than women in the descending trial cohort. The metabolic responses and performance during ascending and descending are summarized in Table 2. Stepping rate is calculated by dividing the 180 steps covered with the time taken to complete the climb. It must be pointed out that the subject’s climb time includes the time taken to traverse the 2-m horizontal landings between each flight of stairs. Men ascended the 11 stories significantly faster but had a lower heart rate than women during the climb. Men also exhibited significantly higher oxygen uptake (in absolute and relative terms) than women during the ascent. During descending, both genders produced similar metabolic responses, except that men had a significantly lower heart rate at the end of the descent.
The correlation values for the various climbing variables are shown in Table 3. Body mass and duration of climb were significantly correlated to absolute oxygen uptake during ascending, in both men and women. The duration of ascending was also significantly correlated to heart rate during ascent in both men and women. In contrast, significant correlations of some of the variables measured were noted only for female subjects in the descending trial. Table 4 shows the calculated energy cost and METs of ascending and descending the stairs.
Responses during ascending and descending.
Figure 1 (A and B) depict a typical subject’s oxygen uptake and heart rate responses every 15 s during ascending and descending the 11 stories, respectively. Ascending responses showed that both V̇O2ascend and HRascend rise markedly for the first 60 s of climbing and tended to level off at about the 90-s mark. A similar pattern of rapid rise and leveling off were demonstrated in another study that had used a public staircase (6). Thus, during ascending, a steady-state response appears to be reached within 90–100 s. In contrast, descending responses were relatively lower and milder, attaining a steady state much earlier.
The mean V̇O2ascend and HRascend were 83% and 89% of the corresponding maximal values attained in the laboratory. The mean V̇O2descend and HRdescend were much lower, equivalent to 39% and 58% of their respective maximal values, apparently due to the complementary use of gravity to assist down stepping. The mean V̇O2ascend and HRascend are well above the recommended minimum intensity values of 50% of V̇O2max or 65% of HRmax for attaining cardiorespiratory benefits set by the American College of Sports Medicine (ACSM) for a broad cross-section of the healthy adult population (3). The mean V̇O2descend and HRdescend clearly do not meet the above guidelines but, however, attain the ACSM minimum threshold of 40% of V̇O2max or 55% of HRmax for the less fit individuals (3). Thus, a practical application of these findings is that stair-climbing exercise (ascending and descending) using the local public staircase achieves the intensity requirements for cardiorespiratory benefits.
During ascending, the positive correlations between absolute V̇O2 and body mass in both genders suggest that a heavier individual would find stair climbing physically more taxing. The positive relationship between body mass and oxygen uptake is in agreement with a previous finding that body mass alone could account for 78% of the variance in oxygen uptake during a bench-stepping exercise (1). A heavier body mass needs to overcome a greater inertia due to gravity resulting in higher oxygen cost. There were also inverse relationships between the climb time of ascending with both V̇O2 and HR. These relationships further indicate that a generally faster ascending pace elicits greater physiological responses in the individual. Our finding is in disagreement with previous studies that showed no significant difference in both heart rate and oxygen uptake when stepping at various cadences, albeit these investigators had used step ergometers rather than actual stairs as the mode of exercise (7,11). In contrast, during descending, there were significant correlations between V̇O2 with body mass and between the duration of climb with HR only in women. These associations are difficult to explain because there were no significant differences in the duration of descent, V̇O2, HR, and stepping rate between men and women and the fact that the observed metabolic perturbations during descending were at best, minimal. We speculate that the higher V̇O2max in women of the ascending cohort versus the women of the descending trial cohort might have influenced these observed relationships.
Obviously, the greater metabolic stress observed during ascending as compared with descending is attributed primarily to the need to overcome gravity. The relatively greater physiological cost observed in those subjects who ascended at a faster rate could simply be due to the greater stride frequency. Stepping faster causes the individual to step harder, especially during the push-off from one step to another. This can possibly lead to a greater recruitment of the faster, less economical muscle fibers but at the expense of higher metabolic cost. This view is partially supported by a previous study that showed faster stepping rates led to a significantly greater vertical impact force during bench-stepping exercise (19).
The energy cost of ascending and descending.
Climbing stairs is an ideal activity to encourage additional caloric expenditure throughout the day because many people can easily find opportunities for climbing. In the present study, the gross oxygen cost of ascending and descending was equivalent to 9.6 and 4.9 METs, respectively. Based on the model proposed by Pate et al. (18) for classifying the METs intensity of physical activities, the ascent and descent would be classified as vigorous and moderate activities, respectively. Compared with other common exercise modes, descent is equivalent to brisk walking at 4.3 km·h−1 and ascent to running at a pace of about 9.6 km·h−1 (2). Our METs values appeared to be slightly high compared with other published data. Ainsworth et al. (2) noted that the intensity of ascending and descending stairs were 8.0 and 3.0 METs, respectively, and Bassett et al. (4) values were 8.6 and 2.6 METs. The kcal expended during the ascent and descent of the 11 stories was calculated to be 19.7 and 9.1 kcal, respectively, or a total of 28.8 kcal. This information is pertinent to the exercising individual who is interested in the amount of calories expended when participating in a weight-management exercise program. To promote weight loss and body fat reduction, the ACSM guidelines suggested that an exercise bout should elicit an expenditure of 300–500 kcal, performed thrice weekly. However, an expenditure of 200 kcal is also viable given that the exercise frequency is increased to four sessions a week (3). To meet the latter requirement, the exercising individual needs to climb up and down the 11 stories for a total of 7 times or a duration of 26 min each session.
The energy cost per step was also calculated. This is relevant given that the number of steps and/or flights of stairs may not be consistent throughout the country. The gross caloric cost of stepping (i.e., ascending and descending a step) is 0.16 kcal·step−1. This calculation was performed without taking into consideration the steps taken to traverse horizontally across the 2-m landing between each flight of stairs. This is much lower than that of Bassett et al. (4) Shephard (20), and Nagle et al. (16) of 0.20, 0.237, and 0.23 kcal·step−1, respectively. There are several plausible reasons for the observed differences in the energy cost of stair climbing among studies. One is the variation in climbing pace. Although stepping rates in the Ainsworth et al. (2) study were not reported, Bassett et al. (4) had used a 70 steps·min−1 stepping rate and Shephard (20) estimated that their stepping rates were 57–76 steps·min−1. The mean stepping rate in the present investigation was higher than previous studies, although it is admitted that our range of stepping rates was wide. Differences in the “stair-climbing equipment” employed could also be another factor to consider. In the present study, we used a public-access staircase whereas others had utilized an escalator (4), a two-level bench (20), and a motorized platform (16), which may affect the efficiency and/or alter the stepping movement pattern. Another reason could be differences in the vertical height of the step that may possibly account for much of the disparity. We had used a step height of 15 cm compared with the higher step height of 20.3 cm in the cited studies.
The intensity of ascending and descending a typical 11-story public housing flat in Singapore is 9.6 and 4.8 METs, respectively. The caloric cost of stepping up and down a step is 0.16 kcal. The present study showed that stair-climbing activity elicits oxygen and heart rate responses that meet the minimum intensity requirements set by ASCM for cardiorespiratory and health gains. Because of the easy accessibility of public staircases, the investigators recommend that it should be promoted aggressively as a suitable and viable exercise activity to the people in Singapore and other communities living in high-rise buildings.
We acknowledge the assistance of Lee Hong Choo in this project.
Address for correspondence: Dr. Teh Kong Chuan, Director, Sports Medicine & Research Center, Singapore Sports Council, 15 Stadium Road, National Stadium, Kallang, Singapore 397718; E-mail: [email protected]
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