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- Halder, Amitava, et al.
(författare)
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Muscle electrical activity changes over time during stair ascending until exhaustion
- 2018
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Ingår i: 22nd Congress of the International Society of Electrophysiology and Kinesiology (ISEK).
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Konferensbidrag (refereegranskat)abstract
- BACKGROUND AND AIM Non-stop stair ascending at maximum speed is required to reach a safe refuge level from deep underground structures, such as subways and in high-rise buildings in an emergency evacuation situation. Endurance of stair climbing and identifying the time of the onset of leg’s local muscle fatigue (LMF) are interests in evacuation research. The objective of this laboratory study was to investigate leg muscles’ electrical activity changes in electromyography (EMG) over time during stair ascending until exhaustion on a stair machine. METHODS The developed muscle activity rate change (MARC) in muscle activity interpretation square (MAIS) was used to evaluate leg LMF at constant step rates equivalent to individual 100% VO2max level. This result is used to validate the MAIS. The MAIS is based on the four assumptions of EMG muscle activity (AMP and MDF) rate change (MARC) over the ascending durations. An increase in AMP and MDF is an indication of: 1) muscle force increase. An increase in AMP and a decrease in MDF is an indication of: 2) muscle fatigue. A decrease in AMP and MDF is an indication of: 3) muscle force decrease. A decrease in AMP and an increase in MDF is an indication of: 4) fatigue recovery. MARC was observed on the both AMP and MDF values of the ten equal length divisions (10%) in the total ascending period (100%). The averages of the MDF and normalized AMP for each equally divided 10% period were calculated for all subjects to yield 1 data point, and totally 10 data points. These 10 periodical average AMP and MDF data points (10-100%) and the changes between the unit times represent the MARC for each muscle during ascension. Later, both the AMP and MDF MARC values are combined to get one final point for each tenth percentile duration and presented into the MAIS, which is used to estimate muscle fatigue.MARC values are derived by the following equation:∆MARC = (x_n-x_(n-1))/(t ̅⁄10) where, ΔMARC is change in a selected parameter (AMP and MDF) over normalized time;x_n is the selected parameter (AMP and MDF) value at each normalized time point n;x_(n-1) is the selected parameter value at a normalized time point n-1;t ̅ is the average duration in seconds for the stair ascending;10 is the total number of normalized times.RESULTS The appearances of MARC points in the MAISs showed the state of muscle activity changes over time during this predetermined and constant ascending speed at 100% of VO2max on a stair machine. Most of the muscles’ MARC points at 90-100% periods were found in the muscle fatigue squares. Moreover, individual AMP and MDF analysis showed significantly increased and decreased, respectively, which supported the interpretations made by the MAIS.CONCLUSIONS These stair ascending EMG results supported the MARC and MAIS when interpreting muscle fatigue. They seem promising to interpret muscle activity changes per unit time during dynamic tasks over the whole working duration in different activities.
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| 2. |
- 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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