Brief Intense Stair Climbing Improves Cardiorespiratory Fitness

Abstract

Purpose 

Sprint interval training (SIT) is a time-efficient strategy to improve cardiorespiratory fitness (CRF); however, most protocols have been studied in laboratory settings and require specialized equipment. We investigated the efficacy of brief intense stair climbing as a practical model of SIT to improve CRF.

Methods 

Two separate studies, each consisting of an acute and chronic phase, were conducted in a total of 31 sedentary women (age = 24 ± 10 yr, body mass index = 23 ± 4 kg·m⁻²).

Results 

The acute phase of study 1 established that the mean HR, blood [lactate], and RPE were similar when participants (n = 8) performed an SIT protocol that involved 3 × 20-s “all-out” efforts of either continuously ascending stairs or cycling. The chronic phase demonstrated that CRF, as determined by peak oxygen uptake (V˙O_2peak), increased by 12% or ~1 MET (8.27 ± 1.05 to 9.25 ± 1.01 METs, P = 0.002) when participants (n = 12) performed the 3 × 20-s stair climbing protocol 3 d·wk⁻¹ for 6 wk. The acute phase of study 2 established that HR and RPE were similar when participants (n = 11) performed three different stair climbing protocols: the 3 × 20-s continuous ascent model used in study 1 and two 3 × 60-s models of ascending and descending either one or two flights of stairs (P > 0.05). The chronic phase demonstrated that V˙O_2peak increased by 7% (8.91 ± 1.30 to 9.51 ± 1.52 METs, P = 0.01) when the same group of participants performed the one-flight 3 × 60-s protocol 3 d·wk⁻¹ for 6 wk. The Cederholm index determined from an oral glucose tolerance test was 57 ± 17 and 64 ± 21 mg·L⁻²·mmol⁻¹·mU⁻¹·min⁻¹ before and after training, respectively (P = 0.056).

Conclusion 

Brief, intense stair climbing is a practical, time-efficient strategy to improve CRF in previously untrained women.

Low cardiorespiratory fitness (CRF) is a strong predictor of cardiovascular disease and all-cause mortality (²¹). Unfit individuals have twice the risk of death from all causes as their fit counterparts, regardless of body mass index (BMI) or body composition (^2,22). Epidemiological evidence has also established that a 1 MET higher CRF is associated with 15% and 13% reductions in risk of cardiovascular disease and all-cause mortality, respectively (²¹). Public health guidelines generally prescribe 150 min of weekly moderate-intensity physical activity to achieve health benefits (¹²). Although this prescription is evidence based (¹²), it may be insufficient to enhance CRF in a substantial portion of the population (³³). Some agencies advocate 75 min of vigorous activity as an alternative to 150 min of moderate activity (¹²). This recommendation is based mainly on the similar energy expenditure for the two prescriptions, as opposed to a specific effect of exercise intensity per se (¹²). Nonetheless, it has been established that high-intensity exercise confers larger improvements in CRF than moderate-intensity exercise when matched for total work (^6,17).

Sprint interval training (SIT), which involves brief intermittent bursts of very intense exercise separated by recovery periods, is also efficacious for improving CRF (^16,34,39,40). As little as two or three 20-s “all-out” sprints, within a 10-min time commitment, can improve CRF by ~1 MET when performed three times per week for 6 wk (^14,15,28,29). One study has also recently shown that 12 wk of training in this manner improved CRF and insulin sensitivity to the same extent as a moderate-intensity continuous exercise protocol that involved a fivefold greater exercise volume and time commitment (¹⁴). Collectively, these studies (^14,15,28,29) are noteworthy given that accelerometer data suggest ≤15% of North American adults meet current physical activity guidelines (^9,36), with perceived “lack of time” commonly cited as a barrier that negatively correlates with physical activity participation (³⁵).

Access to physical activity facilities is another strong correlate of physical activity participation (³⁵). The majority of research demonstrating the efficacy of SIT has been conducted in a laboratory setting using specialized equipment, such as cycle ergometers, which are inaccessible to many individuals. By contrast, stair climbing is a readily accessible form of exercise that offers the potential for SIT to be performed outside the laboratory. Although it has been established that vigorous stair climbing for 30–160 min·wk⁻¹ for 8–12 wk can improve CRF (^3,4,20,24), whether smaller doses of stair climbing performed according to an SIT protocol improves CRF remains unknown.

The present work explored the potential for brief, intense stair climbing to improve CRF and other indices of cardiometabolic health. Two separate but related studies were conducted, each involving an acute and chronic phase. The acute phases assessed physiological and perceptual responses to various SIT protocols using randomized crossover designs. The chronic phases examined the effect of two distinct 6-wk training interventions: the first study involved repeated 20-s bouts of continuously ascending stairs, and the second study involved repeated 60-s bouts of ascending and descending stairs. We tested two main hypotheses: 1) an acute bout of stair climbing would elicit physiological and perceptual responses similar to a modified Wingate-based cycling protocol, and 2) 6 wk of stair climbing would improve CRF, similar to what has been demonstrated for cycling-based SIT.

METHODS

Subjects

Three separate groups of sedentary but otherwise healthy women were recruited (total n = 31). The acute and chronic phases of study 1 were completed at different institutions with separate groups of women, whereas a third group participated in the acute and chronic phases of study 2 (Table 1). Participants were considered sedentary but healthy based on a self-report of ≤1 h of structured physical activity per week using the International Physical Activity Questionnaire and the Physical Activity Readiness Questionnaire (PAR-Q). Physical activity levels were confirmed for the chronic phases by a peak oxygen uptake (V˙O_2peak) <70th percentile (¹). The experimental procedures and associated risks were explained to all subjects before their participation, and all subjects provided written informed consent. The acute phase of study 1 was conducted at Queen's University and approved by Queen's University Health Sciences Research Ethics Board. The remaining phases were completed at McMaster University and approved by the Hamilton Integrated Research Ethics Board.

TABLE 1: Participant characteristics.

Experimental Design

Overview

Two separate studies were conducted, both of which involved an acute exercise comparison and a subsequent 6-wk training intervention. In study 1 (group 1), we initially compared the acute physiological and perceptual responses to an SIT protocol using two different exercise modes. The protocol involved 3 × 20-s “all-out” efforts of either cycling or stair climbing, given that the cycling model was previously shown to enhance CRF when participants trained 3 d·wk⁻¹ for 6 wk (¹⁵). After confirming that the acute physiological and perceptual responses were similar, we subsequently recruited a separate group of participants (group 2) to assess indices of cardiometabolic health before and after 6 wk of training with the 3 × 20-s stair climbing protocol. In study 2 (group 3), we initially compared the acute physiological and perceptual responses to three different stair-climbing protocols: the 3 × 20-s protocol used in study 1 and two other protocols that involved 3 × 60-s of vigorously climbing up and down either one flight (3 × 60-s 1F protocol) or two flights (3 × 60-s 2F protocol) of stairs. The rationale was that the latter two protocols might be easily adapted to a typical home or dwelling with one or two stories, whereas the 3 × 20-s protocol necessitated a building with 3–4 stories and an “all-out” pace. Upon determining that the acute physiological and perceptual responses to the three protocols were similar, and that participants preferred the 3 × 60-s 1F protocol, we assessed indices of cardiometabolic health before and after 6 wk of training with the 3 × 60-s 1F protocol in the same group of participants.

Study 1: acute phase

A randomized crossover design was implemented to compare acute responses to the stair climbing and cycling protocols. Each involved a 2-min warm-up, 3 × 20-s “all-out” efforts interspersed with 2 min of recovery, and a 3-min cooldown. The two trials were separated by ≥24 h. The 20-s stair climbing efforts were performed as a continuous ascent in a local stairwell (120 stairs, stair height = 0.135 m). Participants were instructed to “Climb the stairs as quickly and safely as possible, taking one step at a time.” The warm-up included walking on flat ground at a brisk pace, whereas the recovery periods and cooldown included walking down the stairs and on flat ground at a self-selected pace. The 20-s cycling efforts were performed on a stationary cycle ergometer (Monark Ergomedic 874E Vansbro, Sweden) as previously described (¹⁵) and constituted a modified Wingate test using a resistance equivalent to 5% of body weight. The warm-up, recovery periods, and cooldown involved light cycling against no load (¹⁵). HR was monitored continuously throughout each session, whereas finger prick blood lactate concentration and RPE were measured before the first and immediately after each subsequent 20-s bout.

Study 1: chronic phase

Participants reported to the laboratory on three separate occasions over ~14 d for baseline testing and familiarization. During the initial visit, participants completed a continuous incremental V˙O_2peak test after refraining from food and beverages for ~2 h. At least 4 d later, participants reported to the laboratory after a standardized dinner and 10-h overnight fast for body composition analysis and to provide a resting blood sample for assessment of fasting insulin sensitivity. Body composition was analyzed using air displacement plethysmography (BOD POD; Life Measurement, Inc., Concord, CA). After 1–2 d, participants returned for seated resting blood pressure (BP) measures and to complete the modified Canadian Aerobic Fitness Test (mCAFT). On the same day, participants practiced the 3 × 20-s stair climbing protocol and were given the same instructions as those from the acute phase. Participants then trained 3 d·wk⁻¹ for 6 wk in a local stairwell (99 stairs; stair height = 0.195 m). Warm-up was modified to include a moderately paced climb up and down two flights (i.e., one story or 18 stairs) at a self-selected pace before the brisk walk to ensure an adequate warm-up. During each session, HR was monitored continuously, RPE was recorded before warm-up and after each 20-s bout, and the number of stairs climbed and the vertical work output were recorded for each 20-s bout. All training sessions were supervised. Approximately 72 h after the final training session, body composition and fasting insulin sensitivity were assessed. A V˙O_2peak test and the mCAFT were administered at least 4 and 6 d after the final training session, respectively. Resting BP was measured before the mCAFT test. All procedures were identical with those used during baseline testing.

Study 2: acute phase

The acute phase of study 2 was completed after baseline testing but before training. The immediate exercise responses of two different modified protocols were compared with the 3 × 20-s protocol from study 1 using a William's square (i.e., complete counterbalanced) design. All participants reported to the laboratory on four separate occasions during the course of ~10 d. The first visit included an exercise familiarization session, during which participants were introduced to the RPE scale and each of the three stair-climbing protocols using standardized instructions. Participants practiced climbing at an “all-out” and vigorous pace. During each of the following three visits, participants completed either the 3 × 20-s “all-out” protocol from study 1 or one of the two modified 3 × 60-s vigorous protocols in a local stairwell (61 stairs; stair height = 0.205 m). The 3 × 60-s 1F and 2F protocols involved ascending and descending one flight of 10 stairs and two flights with a total of 18 stairs, respectively. The bouts were extended to 60 s to ensure participants spent at least 20 s ascending stairs, aligning with the 3 × 20-s protocol. Instructions for the 3 × 20-s protocol were the same as those used in study 1, but for the 3 × 60-s protocols, participants were instructed to “Climb up and down the stairs one step at a time for 1 min, ascending vigorously and descending as desired. Vigorous means relatively intense, but not all-out.” The warm-up, recovery, and cooldown periods were the same as the 3 × 20-s protocol in the chronic phase of study 1; however, the recovery periods were shortened to 1 min instead of 2 min. Finger prick samples for blood lactate determination were obtained before warm-up after a seated 5-min rest and immediately after the final 20-s or 60-s bout (no difference in timing between protocols, P = 0.12). Continuous HR, RPE, stairs climbed, and vertical work output were measured for each protocol (as reported in the chronic phase of study 1). Each session was separated by 48–72 h and completed at roughly the same time of day. After completing the acute phase of study 2, participants were asked to rank all three protocols in their order of preference, and the most preferred modified protocol (i.e., 3 × 60-s 1F or 2F) was used for the chronic phase.

Study 2: chronic phase

Because of the nature of recruitment and study design, participants completed two separate pretraining V˙O_2peak tests to account for possible learning effects and enhance validity. The first V˙O_2peak test was completed as a screening measure 6–8 wk before the baseline measures, during which the second V˙O_2peak test was completed to account for possible changes between the screening and the baseline measures. All baseline measures were completed within ~1 wk before the acute phase to avoid possible exercise or training effects as the chronic phase began immediately after the acute phase. After a standardized dinner and a 10-h overnight fast, participants reported to the laboratory for body composition analysis (as reported in study 1) and an oral glucose tolerance test (OGTT). Participants returned 1–2 d later after another overnight fast for seated resting BP measures, along with the second V˙O_2peak test. Participants trained 3 d·wk⁻¹ for 6 wk using the 3 × 60-s 1F protocol in the same stairwell as the acute phase, with continuous HR, RPE, number of stairs climbed, and vertical work output recorded for each session (as reported in the chronic phase of study 1). Approximately 72 h after the last training session, participants returned to the laboratory for body composition analysis and an OGTT. Participants returned ~24 h later for resting BP measurements, as well as a final V˙O_2peak test. All procedures were identical and completed at the same time of day (±0–3 h) as the baseline measures. In attempt to control for menstrual cycle, baseline and posttraining measures were scheduled approximately two full cycles apart (~8 wk, accounting for individuals' cycle duration); however, the variability within participants' cycles and the time sensitivity of posttraining measures prevented control within ±5 d for most participants.

Measurements

V˙O_2peak test

Participants performed an incremental test to exhaustion on an electronically braked cycle ergometer (Lode Excalibur Sport V 2.0, The Netherlands) to directly measure V˙O_2peak and peak power output (PPO) as previously described (^14,15). After a 1-min warm-up at 50 W, power output increased by 1 W every 2 s until the pedal cadence fell less than 50 rpm. Oxygen consumption and carbon dioxide production were analyzed with a metabolic cart (Moxus; AEI Technologies, Pittsburgh, PA), and the greatest 30-s average was recorded as V˙O_2peak. Tests were considered valid if two or more of the following criteria were met: a plateau in V˙O₂ despite increasing intensity, RER > 1.1, HR within 10 beats of age-predicted maximum, and/or volitional exhaustion.

mCAFT

The mCAFT was used as a practical method to estimate V˙O_2peak, as might be encountered in a clinical or training setting. According to standardized procedures (⁷), participants completed one or more 3-min stages of stepping using a set of two steps (0.203 m). The frequency of stepping was predetermined (based on age and gender) and increased as the test progressed. The test ended when participants achieved or exceeded 85% of their age-predicted maximum HR at the end of a 3-min stage.

Resting BP

BP was measured in triplicate while seated using an automatic oscillometric device in study 1 and study 2 (Contec 08A, Qinhaungdo, China, and Omeron BP765CAN, Kyoto, Japan, respectively), according to the standardized technique recommended by the Canadian Hypertension Education Program (¹⁰). Briefly, participants sat quietly in a room free from any distractions or interruptions for 10 min before three measurements that were separated by ~1 min. BP was determined from an average of the latter two measurements.

Blood sampling

Participants consumed a standardized meal the evening before an overnight fast. In study 1, a fasting sample was obtained from an antecubital vein via venipuncture. For study 2, a standard seven-sample OGTT was performed (⁸). An indwelling catheter was inserted into an antecubital vein, and a fasting blood sample was obtained before ingestion of a 75-g glucose drink (NERL^TM Trutol^TM; Thermo Fisher Scientific Inc., Waltham, MA), followed by blood samples collected at 10, 20, 30, 60, 90, and 120 min postingestion. Plasma and serum were separated by centrifugation (10 min at 1500g) and stored at −80°C for subsequent analysis. Plasma samples were sent to the Core Laboratory (Hamilton Research Laboratory Medicine Program) for glucose analysis in study 1, and plasma glucose was determined using the glucose oxidase method with a glucose analyzer (YSI Stat 2300, Yellow Springs, OH) in study 2. Insulin was measured by ELISA (ALPCO Immunoassays, Salem, NH). The area under the curve (AUC) for glucose and insulin was calculated using the trapezoidal rule, and insulin sensitivity was calculated using the homeostatic (ISI-HOMA) (²⁶) and the Cederholm models (ISI-Cederholm) (⁸).

Exercise and training measures

HR was monitored continuously throughout every session (PolarTeam System; Polar Electro OY, Kempele, Finland). Participants reported their RPE using the Borg category ratio scale (0–10) in the acute phase of study 1 and the 6–20 scale (⁵) for all subsequent phases. The RPE scale was altered from the 1–10 scale to the 6–20 scale after analysis of the first phase in attempt to align RPE and HR responses more accurately (⁵). Blood lactate concentration was measured using regular finger prick methods with portable lactate analyzers (Lactate Plus; Nova Biomedical Corporation, Cheshire, UK). For stair climbing, the number of stairs climbed and the vertical work output (work [kJ] = body mass [kg] × 9.81 [m·s⁻²] × height [m]/1000) were calculated for each session. For cycling, the mechanical work output was calculated according to the manufacturer.

Statistical Analysis

Results are expressed as mean ± SD. For the acute phase of study 1, n = 8 for all measures except for HR (n = 6) because of technical difficulties. For the chronic phase of study 1, n = 12 for all measures. For the acute phase of study 2, n = 11 for all measures except peak HR (n = 9) and work output (n = 10) because of technical difficulties. For the chronic phase of study 2, n = 11 for all measures except for resting BP (n = 10), owing to participant unavailability at the requisite testing time. A two-way repeated-measures ANOVA was used to test for differences in work output, peak HR, blood lactate concentration, and RPE in the acute phases of study 1 (3 × 2 time by mode for work output and peak HR; 4 × 2 time by mode for blood lactate and RPE) and study 2 (3 × 3 time by protocol for work output and peak HR; 2 × 3 time by protocol for blood lactate; 4 × 3 time by protocol for RPE). A one-way repeated-measures ANOVA was used to test for differences in mean HR between protocols in the acute phase of study 2, as well as mean HR, RPE, and total stairs climbed across weeks in the chronic phase of studies 1 and 2. The Greenhouse–Geisser correction was used when data did not meet the assumption of sphericity, and post hoc analyses were completed using Bonferroni correction. A paired t-test was used to compare the mean HR in the acute phase of study 1, as well as all pre- and posttraining measurements in the chronic phases. Spearman's rho was used to test for associations between direct and estimated (i.e., mCAFT) V˙O_2peak values, given that the data were not normally distributed. The exercise training measures reported for the chronic phases (i.e., stairs climbed, RPE, and HR) are presented as averages from all training sessions, unless otherwise stated. The level of significance for all analyses was set at P ≤ 0.05.

RESULTS

Study 1

Acute phase

Mean HR was similar between the stair climbing and cycling protocols (P = 0.40; Fig. 1A). Peak HR, blood lactate, and RPE values increased with each subsequent bout (P < 0.01; Table 2). There was an interaction between mode and time for RPE (P = 0.002) and peak HR (P = 0.04), such that stair climbing elicited a lower RPE before bout 1 (P < 0.01), and a higher peak HR was after bouts 1 and 2 (P < 0.05). The increase in lactate with each bout was not different between mode (P = 0.40). Vertical work output was greater during stair climbing compared with cycling (main effect for mode, P = 0.01; Table 2).

FIGURE 1: HR responses during the acute exercise sessions. Mean HR response for the acute exercise sessions in study 1 (A) and study 2 (B), including the last 30 s of warm-up, the bouts and recoveries, and the first 30 s of cooldown. SC, stair climbing; CYC, cycling; F, flight; black hashed lines represent the 20-s bouts; gray hashed lines represent the 60-s bouts.

Chronic phase

Participants completed 99% of all training sessions without incident, with one participant completing only 16/18 sessions. Participants climbed 58 ± 4 stairs (11.4 ± 0.8 m) during each 20-s bout. There was a main effect of time across weeks for total stairs climbed each session (P < 0.001), such that participants improved by 7% from weeks 1 to 6 (168 ± 14 to 180 ± 11 stairs per session, P = 0.001). There was also a main effect of time for average RPE (P = 0.02), which significantly increased from 13.6 ± 1.4 in week 1 to 14.4 ± 1.6 in week 3 (i.e., “somewhat hard–hard” for both, P = 0.005), with no further increase thereafter (P ≥ 0.08). Participants fatigued by 14% ± 4% from the first to the last 10 s within bouts and by 7% ± 4% from bouts 1 to 3. When averaged across the 20-s bouts, HR was 82% ± 4%, 88% ± 3%, and 90% ± 3% of maximum for bouts 1–3, respectively. The mean HR for the entire 10 min session was 81% ± 4% of max HR, with no effect of time across weeks (P = 0.65).

V˙O_2peak measured directly increased by 12% after training (1.80 ± 0.25 to 2.02 ± 0.27 L·min⁻¹, P < 0.001; Fig. 2A), and this was associated with an 8% increase in PPO (P < 0.001, Table 3). V˙O_2peak estimated from the mCAFT increased by 4% (P = 0.007; Table 3), and there was a 5% attenuation in the HR response to the first stage of the mCAFT after training (152 ± 17 to 147 ± 21 bpm, P = 0.01). There were no correlations between direct and estimated V˙O_2peak (calculated from the mCAFT) for pretraining (r = 0.51, P = 0.09), posttraining (r = 0.13, P = 0.68), and change in V˙O_2peak (r = 0.35, P = 0.26). There were no training-induced changes in resting systolic BP (P = 0.82), diastolic BP (P = 0.97), mean arterial BP (P = 0.86), BMI (P = 0.39), body mass (P = 0.35), fat-free mass (P = 0.09), fat mass (P = 0.70), % body fat (P = 0.42), fasting glucose concentration (P = 0.15), fasting insulin concentration (P = 0.31), or HOMA-IS (P = 0.52; Table 3).

FIGURE 2: V˙O_2peak measured before and after 6 wk of 3 × 20-s and 3 × 60-s 1F. Measured at baseline (PRE) and after 6 wk of training (POST) with the 3 × 20-s (A) and 3 × 60-s 1-flight (B) protocols. Values are mean ± SD. Gray lines represent individual subjects; **P ≤ 0.001 vs PRE.

TABLE 2: Acute exercise responses.

TABLE 3: Cardiometabolic measures pre- and posttraining.

Study 2

Acute phase

Mean HR was similar between all three stair climbing protocols (P = 0.20; Fig. 1B). Peak HR, lactate, and RPE values increased with each subsequent bout (P < 0.01; Table 2). There was a significant interaction between protocol and time for lactate (P = 0.001), such that the 3 × 20-s protocol elicited a higher concentration after the third bout compared with the 3 × 60-s 1F and 2F protocols (P < 0.01; Table 2). Vertical work output was lower during the 3 × 20-s protocol compared with the 3 × 60-s 1F and 2F protocols (main effect for protocol, P < 0.001; Table 2), which correspond to an average of 53 ± 6, 74 ± 8, and 71 ± 6 stairs climbed per bout, respectively.

Chronic phase

Participants completed 100% of all training sessions without incident. Participants spent 27 ± 3 s ascending 8 ± 1 flights of 10 stairs (16.7 ± 2.1 m) and 33 ± 3 s descending each 60-s bout (times based on third and final sessions). There was a main effect of time (P < 0.001) for total stairs climbed each session, such that participants improved by 11% from week 1 to week 6 (232 ± 26 to 257 ± 30 stairs, P < 0.001). The average RPE elicited for each session was 14.3 ± 1.2 (i.e., “somewhat hard–hard”), with no main effect of time across weeks (P = 0.54). Participants fatigued by 10% ± 4% from the first to the last ascent within bouts and by 4% ± 3% from bouts 1 to 3. When averaged across the 60-s bouts, HR was 81% ± 6%, 89% ± 4%, and 93% ± 3% of maximum for bouts 1–3, respectively. The mean HR for the entire 10 min session was 80% ± 4% of max HR, with no effect of time across weeks (P = 0.44).

After training, absolute V˙O_2peak measured directly increased by 8% from baseline (1.79 ± 0.37 to 1.93 ± 0.39 L·min⁻¹, P = 0.001; Fig. 2B), and this was associated with a 9% increase in PPO (P < 0.001; Table 3). There were no differences between screening and baseline V˙O_2peak (1.76 ± 0.34 L·min⁻¹, P = 0.37) and PPO (170 ± 33, P = 0.44). There was a significant increase in BMI (P = 0.02), body mass (P = 0.05), and fat-free mass (P < 0.001) but no change in fat mass (P = 0.36) or % body fat after training (P = 0.10; Table 3). Systolic, diastolic, and mean arterial BP were unchanged (P = 0.50, P = 1.00, and P = 0.96, respectively; Table 3). There were no training-induced changes in OGTT-derived parameters, including mean glucose (P = 0.20) and insulin (P = 0.07) concentrations, AUC for glucose (P = 0.35) and insulin (P = 0.20), fasting glucose (P = 0.52) and insulin (P = 0.35) concentrations, HOMA-IS (P = 0.59), or the ISI-Cederholm (P = 0.056; Table 3).

DISCUSSION

The major novel finding of the present work is that brief, intense stair climbing is a time-efficient strategy to increase CRF. V˙O_2peak increased by ~1 MET after 6 wk of training using the protocol used in study 1, which involved 3 × 20-s bouts of continuously ascending stairs interspersed with 2 min of recovery. The 12% improvement in V˙O_2peak for 6 wk was strikingly similar to the improvement reported by Gillen et al. (¹⁵), who used the same protocol, but used a cycle ergometer to train participants. The protocol used in study 2, which involved 3 × 60-s bouts of ascending and descending one flight of stairs, interspersed with 60 s of recovery, improved V˙O_2peak by 8%. These data demonstrate that stair climbing is an efficacious model of SIT for improving CRF, making it a practical alternative to cycling-based SIT.

Previous studies have reported that ascending stairs for 30–70 min each week for 8 wk can improve CRF (^3,4,20,24). The total time spent ascending and descending stairs in the present study was much lower amounting to ≤9 min·wk⁻¹, with only ~3 min of ascending stairs each week. When the time required to complete warm-up and cooldown is included, the total time commitment amounts to 30 min·wk⁻¹. Because of the influence of perceived “lack of time” and lack of access to specialized facilities on physical activity participation (³⁵), it is important to identify time-efficient exercise protocols that do not require special equipment. Before the present work, few studies have assessed the efficacy of SIT outside a laboratory setting (²⁵) and without the use of specialized exercise equipment (^25,27). Given that SIT has been established as a time-efficient strategy for improving CRF (^16,34,39,40), the intent of the present work was to assess the efficacy of SIT when adapted to stair climbing because it is an accessible form of exercise that could be easily adopted into daily routine.

Similar Acute Responses to Stair Climbing and Cycling-Based SIT

The acute exercise data from study 1 of the present investigation suggests that stair climbing and cycling-based SIT elicit a similar metabolic stress. By contrast, Oldenburg et al. (³¹) reported that the accumulation of blood lactate during stair climbing was less than that during cycling; however, they matched power output for the two modes of exercise. Given that the HR and V˙O₂ were similar between stair climbing and cycling (³¹), the higher blood lactate concentration during cycling was likely a result of recruiting a greater proportion of the leg musculature (i.e., more type II fibers and a greater reliance on anaerobic metabolism) as cycling relies on less total muscle mass to generate the same power as stair climbing. The similar lactate concentrations reported in study 1 of the present investigation align with Oldenburg et al. (³¹) because participants generated more power output during stair climbing as compared with cycling. The higher power output generated during stair climbing was associated with a generally higher peak HR; however, there were no differences in perceived exertion across modes. Together, these data suggest that when cycling-based SIT protocols are transferred to stair climbing, they still elicit similar, if not greater, acute physiological responses.

Six Weeks of Stair Climbing Improves CRF by 1 MET

Low CRF has greater consequences than hypertension, smoking, obesity, and hyperlipidemia in terms of risk for adverse health outcomes (¹⁹). Although athletes have long used interval training to improve fitness (¹⁸), there has been a renewed interest in SIT due, in part, to the health benefits that can be achieved with low volumes of exercise. Gist et al. (¹⁶) concluded that despite the reduced volume of work, SIT, and traditional endurance training are equally effective for improving V˙O_2peak, citing a collective improvement of 8% (~3.6 mL·kg⁻¹·min⁻¹) within 2–6 wk of training. We found that 6 wk of brief and intermittent bouts of “all-out” stair climbing increased relative V˙O_2peak by 12% or ~1 MET (i.e., 3.5 mL·kg⁻¹·min⁻¹). Dose–response analyses suggest that a 1-MET higher V˙O_2peak is comparable with having a 7-cm lower waist circumference, a 5-mm Hg lower systolic BP, or a 1-mM lower fasting plasma glucose in terms of risk for all-cause mortality and cardiovascular disease (²¹).

The improvements in CRF in the present work are similar to previous stair climbing studies using higher-volume and lower intensity protocols (^3,20,24); however, to our knowledge, only two studies have directly measured aerobic capacity (^3,24), the gold standard in fitness assessment. Of these two studies, Boreham et al. (³) evaluated a lower-volume protocol and reported that sedentary women improved their relative V˙O_2peak by 17% (4.5 mL·kg⁻¹·min⁻¹) after 8 wk of training; however, in addition to a longer training period, peak training volume was ~825 m·wk⁻¹ at a rate of ~15 m·min⁻¹, versus 100–150 m·wk⁻¹ at a rate of 34–37 m·min⁻¹ in the present investigation. This ~7-fold difference in total work per week and only ~2-fold difference in climbing speed supports the idea that intensity has a greater effect than total work (i.e., training volume) for improving aerobic capacity (^13,14).

Given the applied nature and goals of this investigation, the mCAFT was used as a more practical and realistic assessment of CRF that may be encountered in the field. We found that the mCAFT overestimated V˙O_2peak, the improvements detected by the mCAFT were much smaller compared with the direct V˙O_2peak test, and correlations between mCAFT and direct V˙O_2peak values were poor. Although a previous study concluded that the mCAFT was valid for the general population, it demonstrated low specificity for participants with poor fitness (³⁸), which agrees with the overestimated values in our study (~20%). Modifying the mCAFT might improve its accuracy for individuals with poor fitness; however, further research with a larger sample size is necessary.

Other Health-Related Markers

The stair climbing protocols did not improve measures of insulin sensitivity based on fasting blood samples. Glucose and insulin concentrations measured during OGTT tests were also unchanged; however, the increase in OGTT-derived insulin sensitivity approached significance (P = 0.056). The lack of improvement in the fasting measures is in contrast to the results of Gillen et al. (¹⁵) but align with Metcalfe et al. (^28,29). The discrepancies could be due in part to subject characteristics, as the women were overweight in Gillen et al. (¹⁵) compared with the women in Metcalfe et al. (^28,29) and the present study. It was also previously reported that OGTT-derived insulin sensitivity (^28,29), and indices of glycemic control based on continuous glucose monitoring (¹⁵) were unchanged in women after cycling-based SIT. Menstrual cycle phase may also influence insulin sensitivity. When plasma estradiol levels were increased by ~200%, insulin action was increased by 20% in postmenopausal women when compared with a control trial (³⁷); however, this may not apply to premenopausal women. Although we attempted to control for menstrual cycle in study 2, the variability of menstrual cycles and logistical issues of time-sensitive measures prevented such control for most of the women.

Body composition was unchanged after 6 wk of training with the 3 × 20-s “all-out” protocol; however, there were small but significant increases in fat-free mass, total body mass, and BMI after 6 wk of training with the 3 × 60-s 1F protocol. The reason for the discrepancy is unclear, but the lack of change in body mass and BMI with the 3 × 20-s protocol is consistent with previous research (^15,28,29) that used similar cycling-based protocols. We found no changes in BP for either the 3 × 20-s or 3 × 60-s 1F protocols, which contrasts with the results by Gillen et al. (¹⁵). This may be due to the fact that the participants in the current study were younger and not overweight. Given that both groups in the current study presented with healthy BP measures at baseline (¹⁰), the potential to further decrease values with just 6 wk of training is likely minimized.

Protocol Modifications

The aim of study 2 was to improve the practicality of the 3 × 20-s “all-out” protocol so that it could be completed at a submaximal pace in a house or small building, while still eliciting a similar improvement in CRF. The 20-s bouts of continuously ascending as fast as safely possible (~60 stairs or ~3 stories) were adjusted to 60 s of vigorously climbing up and down one or two flights (10–18 stairs or ~1 story). The 3 × 20-s and 3 × 60-s protocols elicited a similar RPE, peak HR after each bout, and mean HR for the entire 10-min sessions, potentially owing to the decreased climbing pace but increased exercise duration. Interestingly, most participants preferred the 3 × 20-s protocol over the 3 × 60-s protocols, and most of the participants chose the 3 × 60-s 1F protocol over the 2F. Many participants reported that they were required to turn too many corners during the 2F protocol, which sometimes led to feelings of instability.

Stair Climbing Is a Practical Model of SIT

Stair climbing is likely to be an effective form of exercise given that public health physical activity initiatives are effective when they are lifestyle based (¹¹), and the total stairs climbed each week independently predicts risk of cardiovascular disease and all-cause mortality (²³). Stair climbing is also likely to be more practical than cycling and running-based SIT protocols for the general population because it can be completed outdoors and indoors in private and public settings with no associated costs. Opdenacker et al. (³²) demonstrated that lifestyle-based physical activity interventions (i.e., integrated into daily routine and home-based programs supported by telephone calls) are just as efficacious but more effective than structured physical activity interventions (i.e., supervised in a fitness facility) such that maintenance of CRF was better 2 yr after intervention. Stair climbing-based SIT is also practical because climbing stairs is an important but neglected skill that is necessary for maintaining mobility and independence throughout the life span (³⁰). Furthermore, the stair climbing protocols used in this investigation are based on individuals' perceived exertion and therefore can elicit an appropriate stimulus for many different fitness levels. Subjects in the present study completed training sessions without any incident, suggesting that brief and intermittent bouts of stair climbing are a tolerable and appropriate form of exercise for sedentary adults.

CONCLUSION

In summary, we report that a 10-min exercise protocol involving a total of 1–3 min of intermittent stair climbing improved CRF when performed 3 d·wk⁻¹ for 6 wk. The investigation demonstrates that stair climbing represents a model of low-volume SIT that is efficacious when performed outside a laboratory setting. We recognize that training was not completed in free-living conditions, and therefore future studies should assess the retention and effectiveness of home or work-based SIT using stair climbing with larger sample sizes. The conclusions that can be made from our data are 1) the acute physiological and perceptual responses to “all-out” stair climbing and cycling SIT are similar; 2) brief and intermittent bursts of stair climbing can markedly improve CRF in 6 wk, similarly to cycling-based protocols; and 3) despite the low volume of exercise, an all-out pace was not necessary to improve CRF. With a minimal weekly time-commitment of 30 min, brief and intermittent bouts of intense stair climbing are a plausible alternative to cycling-based SIT.

This study was supported by internal research grants from McMaster University and Queen's University. The authors have no conflicts of interest to disclose. The results of the present study do not constitute endorsement by the American College of Sports Medicine. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.