Abstract
Stair-ascending at maximum ability is required during emergency evacuations to reach a safe refuge from deep underground structures. We hypothesized that an ascent can last maximum 5 min at the individual’s maximum step rate (SR), and oxygen uptake ( {dot{V}}{text{O}}_{2} ) would not reach a stable state. This study explored stair-ascending endurance and some physiological constraints of performance. Eighteen healthy volunteers with mean (standard deviation, SD) age 26.7 (4.0) years, height 172.2 (10.7) cm, weight 68.0 (11.3) kg, BSA 1.8 (0.2) m−2, {dot{V}}{text{O}}_{rm 2max} 48.5 (5.4) mL min−1 kg−1, and HRmax 192 (9) b min−1 ascended on a stair machine at a SR equivalent to their 100% {dot{V}}{text{O}}_{rm 2max} . The mean (SD) ascending duration was 3.47 (1.18) min, supporting the hypothesis. The calculated vertical height covered was 85.5 (32.1) m. The {dot{V}}{text{O}}_{rm 2highest} reached 44.8 (7.3) mL min−1 kg−1, which was 92.3 (9.7)% of {dot{V}}{text{O}}_{rm 2max} when the HRhighest peaked at 174 (11) b min−1. However, the mean ( {dot{V}}{text{O}}_{2} ) reached a relatively steady state after the sharp rise. The post-ascent blood lactate, respiratory exchange ratio, and perceived exertion values recorded were high, 14.4 (4.0) mmol l−1, 1.20 (0.09), and 18.2 (0.7), respectively, indicated that exhaustion was reached. The ascending SR rate was above the lactate threshold; therefore, the attainment of {dot{V}}{text{O}}_{rm 2} steady state was slowly reached. EMG amplitudes of four major leg muscles increased and the median frequencies of two muscles decreased significantly (p < .01) indicating local muscle fatigue (LMF). Leg LMF and hyperventilation resulted in speedy exhaustion leading to termination. These results infer that stair ascending at maximum ability (122 steps min−1) is possible to sustain 2–6 min. These overall results offer useful and vital information to consider when designing underground emergency evacuation facilities.
Highlights
Stair-ascending is a frequently encountered demanding task in our daily life [35, 45, 46]
The average ascending duration was 3.5 min and the vertical height reached was 85.5 m with an ascending speed 0.66 m s-1, when the subjects performed a simulated stair ascent evacuation at the constant step rate (SR) of 122.2 steps min-1. These indicate the maximal ascending endurance and threshold in terms of duration and vertical height, when the subjects need to stop after ascending at their maximum speed
The recorded average highest oxygen uptake (V_O2highest) during ascending was 44.8 mL min-1 kg-1 while the highest heart rate (HR) peaked at 174 b min-1, which were lower than the subjects V_O2max and HRmax
Summary
Stair-ascending is a frequently encountered demanding task in our daily life [35, 45, 46]. It requires high physical capacity for the larger thigh muscles to bear the whole body weight against the gravity [2, 16]. Non-stop ascending at maximum speed can be required when people respond to the demands that arise in emergency evacuations for example, terror attacks or fire incidents. People would choose their maximal possible step rate (SR) to reach a safe refuge when they need to ascend from deep underground structures, such as subways, or exits at the higher levels or rooftop in high-rise buildings.
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