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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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Oxygen uptake and muscle activity limitations during stepping on a stair machine at three different climbing speeds
- 2018
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Ingår i: Ergonomics. - : Informa UK Limited. - 0014-0139 .- 1366-5847. ; 61:10, s. 1382-1394
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Tidskriftsartikel (refereegranskat)abstract
- This laboratory study examined human stair ascending capacity and constraining factors including legs’ local muscle fatigue (LMF) and cardiorespiratory capacity. Twenty-five healthy volunteers, mean age 35.3 years, with maximal oxygen uptake (VO2max) of 46.7 mL·min-1·kg-1, and maximal heart rate of 190 bpm, ascended on a stair machine at 60% and 75% (3 min each), and 90% of VO2max (5 min or until exhaustion). The VO2, HR and electromyography (EMG) of the leg muscles were measured. The average VO2highest reached 43.9mL·min-1·kg-1,and HRhighest peaked at 185 bpm at 90%of VO2max step rate (SR). EMG amplitudes significantly increased at all three levels, p<0.05, and median frequencies decreased mostly at 90% of VO2maxSR evidencing leg LMF. Muscle activity interpretation squares were developed and effectively used to observe changes over time, confirming LMF. The combined effects of LMF and cardiorespiratory constraints reduced ascending tolerance and constrained the duration to 4.32 minutes.
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| 3. |
- Svensson, Ingrid, et al.
(författare)
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Balance in standing on inclined surfaces with different friction
- 2018
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Ingår i: Industrial Health. - : National Institute of Industrial Health. - 1880-8026 .- 0019-8366. ; 56:4, s. 292-299
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Tidskriftsartikel (refereegranskat)abstract
- Working and walking environments often involve standing positions on different surfaces with inclination and different friction. In this study, standing balance of thirteen participants during sudden and irregular external perturbation to calf muscles while standing was investigated. The aim of the study was to evaluate the combined effect of surface inclination and friction on standing balance. The main findings when eyes closed revealed that the standing utilised coefficient of friction (μSUCOF) increased when the surface was inclined for both high and low friction materials. The anterior-posterior torque increased more anteriorly when the surface was inclined toes down and when the surface friction was low. The results indicate that the anterior-posterior torque is a sensitive parameter when evaluating standing balance ability and slip risk. On inclined surface, particularly on the surface with lower friction, the potential slip and fall risk is higher due to the increase of standing utilised coefficient of friction and increased forward turning torque.
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| 4. |
- Svensson, Ingrid, et al.
(författare)
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Standing balance on inclined surfaces with different friction
- 2018
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Ingår i: Industrial Health. - : National Institue of Occupational Safety & Health, Japan. - 0019-8366 .- 1880-8026. ; 56:4, s. 292-299
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Tidskriftsartikel (refereegranskat)abstract
- Working and walking environments often involve standing positions on different surfaces with inclination and different friction. In this study, standing balance of thirteen participants during sudden and irregular external perturbation to calf muscles was investigated. The aim of the study was to evaluate the combined effect of surface inclination and friction on standing balance. The main findings when eyes closed revealed that the standing utilised coefficient of friction (mu(SUCOF)) increased when the surface was inclined for both high and low friction materials. The anteriorposterior torque increased more anteriorly when the surface was inclined toes down and when the surface friction was low. The results indicate that the anterior posterior torque is a sensitive parameter when evaluating standing balance ability and slip risk. On inclined surface, particularly on the surface with lower friction, the potential slip and fall risk is higher due to the increase of standing utilised coefficient of friction and increased forward turning torque.
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