Physiological Capacity During Simulated Stair Climbing Evacuation at Maximum Speed Until Exhaustion

Abstract

AbstractStair-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 $$ ( {\dot{V}}{\text{O}}_{2} ) $$ ( V ˙ 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, $$ {\dot{V}}{\text{O}}_{\rm 2max} $$ V ˙ O 2 max 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% $$ {\dot{V}}{\text{O}}_{\rm 2max} $$ V ˙ O 2 max . 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 $$ {\dot{V}}{\text{O}}_{\rm 2highest} $$ V ˙ O 2 highest reached 44.8 (7.3) mL min−1 kg−1, which was 92.3 (9.7)% of $$ {\dot{V}}{\text{O}}_{\rm 2max} $$ V ˙ O 2 max when the HRhighest peaked at 174 (11) b min−1. However, the mean $$ ( {\dot{V}}{\text{O}}_{2} ) $$ ( V ˙ 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 $$ {\dot{V}}{\text{O}}_{\rm 2} $$ V ˙ O 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.