| 1. |
- Halder, Amitava, et al.
(författare)
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Physiological Capacity During Simulated Stair Climbing Evacuation at Maximum Speed Until Exhaustion
- 2020
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Ingår i: Fire Technology. - : Springer Science and Business Media LLC. - 0015-2684 .- 1572-8099.
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Tidskriftsartikel (refereegranskat)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 (V˙O2) 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, V˙O2max 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% V˙O2max. 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 V˙O2highest reached 44.8 (7.3) mL min−1 kg−1, which was 92.3 (9.7)% of V˙O2max when the HRhighest peaked at 174 (11) b min−1. However, the mean V˙O2 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 V˙O2 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
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| 2. |
- Halder, Amitava
(författare)
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The Fight on the Flights : Emergency evacuations – human physiological performance, leg muscle activity and gait biomechanics during exhaustive stair and slope ascent
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Physical exhaustion can constrain stair ascending capacity during emergency evacuation. The overall aim of this research was to explore and compare stair ascending capacities and physiological limitations when using two different modes: 1) self-preferred pace on three different public stairways, and 2) four machine-controlled paces on a stair machine corresponding to different percentages of maximal aerobic capacity (V̇O2max). After the exhaustive stair ascent, gait biomechanics were also studied when walking on an inclined metal walkway in the laboratory. Participants of different ages, genders and body sizes were recruited from social media. The specific objective was to determine, through the combined analysis of oxygen uptake (V̇O2) and electromyography (EMG), how cardiorespiratory capacity and local muscle fatigue (LMF) in the leg constrain the ascending capacity and affect walking gait kinetics and kinematics.The results showed that the average relative maximum oxygen uptake during stair ascent (V̇O2highest) reached 39-41 mL·min-1·kg-1 at the self-preferred pace in the field, and 44-45 mL·min-1·kg-1 at the controlled step rate (SR) corresponding to 90-100% V̇O2max in the laboratory. During ascent at the self-preferred pace, both V̇O2highest and heart rate (HRhighest) reached about 83-95% level of average human capacity reported in literature. During ascent at 90-100% V̇O2max SRs, the V̇O2highest reached about 92-94% of V̇O2max, while HRhighest peaked between 91 and 97% of HRmax. The SR was sustained at 92-95 steps·min-1 at the self-preferred pace on the stairs to complete the ascents in a 13-floor and 31-floor building. The average ascending durations of 4.3 and 3.5 minutes were recorded at an average SR of 109 and 122 steps·min-1 corresponding to 90 and 100% V̇O2max, on the stair machine. A physiological evacuation model was developed based on individual V̇O2max. The model proved to be useful in estimating step rate and vertical displacement, thus it is recommended for calculating the performance as such speed, height during stair ascent evacuation. The EMG amplitudes (AMPs) were different between the self-paced and controlled ascending speeds. During self-preferred ascent, the leg muscle AMPs showed a decreasing trend and the median frequencies (MDFs) were unchanged or slightly decreased indicating reductions of muscle power production and possible fatigue compensation by speed reduction. This allowed recovery to complete the ascents. In contrast, a significant increase of AMPs and decrease of MDFs were observed in the controlled paces evidencing the leg LMF. A muscle activity interpretation squares (MAIS) model was developed by plotting the muscle activity rate change (MARC) percentile points to interpret dynamic muscle activity changes and fatigue over time. At the self-preferred paces, the MARC points in the MAIS reflected recovery from muscle fatigue through power decrease and pace reduction. At the controlled paces, in contrast, the MARC points reflected muscle fatigue. Thus, MARC and MAIS are useful for observing muscle activity changes during repetitive tasks. Constant ascents at maximal intensity (90-100% V̇O2max) resulted in high lactate production and leg LMF due to high demand and insufficient recovery. This forced the subjects to stop within 5-min. The results infer that the combined effect of cardiorespiratory capacity exaggerated by leg LMF constrained stair ascending capacities, durations and vertical distances, thus restricting the V̇O2 uptake from reaching the V̇O2max, while any recovery can extend the tolerance. Finally, when walking up a 10° inclined surface after exhaustive stair ascent, the peak gait ground reaction forces, peak and minimum foot absolute angles, peak foot angular velocity and acceleration all significantly decreased with an increased required coefficient of friction. The altered gait biomechanics on inclines can affect the human locomotion and impede the evacuation process during emergencies.
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| 3. |
- Velasco, Alejandra, et al.
(författare)
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The impact of carrying load on physical performance during ascending evacuation movement
- 2020
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Ingår i: Fire and Materials. - : Wiley. - 1099-1018 .- 0308-0501.
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates how ascending movement is affected by carrying load during a stair‐climbing motion. The methods adopted are based on exercise physiology and fire safety engineering. Experiments with 21 volunteers with mean (SD) age of 27 (4) have been carried out on a stair machine with or without carrying a mass of 8 kg, typical weight of a hand luggage or the average weight of an 8‐months old infant. Oxygen uptake (V˙O2), heart rate (HR), metabolic rate (M), and perceived exertion results showed a decrease in performance in the scenario with additional load. Participants climbed an average of 92 m without carrying a load, in comparison to 84 m when they were carrying it in a 5 minutes task. An average increase of 4% in the V˙O2 and the HR was found in the experiments with the additional mass. The strongest correlating variables observed were M and the vertical distance covered. Differences in perceived exertion occurred after four minutes into the exercise, with higher values in the case with additional load. These results show the need for considering the negative impact of carrying load while designing infrastructures in case of ascending evacuation and while developing evacuation modelling tools.
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