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Title: Muscle activation during exercise in severe acute hypoxia: Role of absolute and relative intensity
Authors: Torres-Peralta, Rafael 
Losa-Reyna, José
González-Izal, Miriam
Perez-Suarez, Ismael
Calle-Herrero, Jaime
Izquierdo, Mikel 
Calbet, Jose A. L. 
UNESCO Clasification: 241106 Fisiología del ejercicio
Keywords: Mean Power Frequency
Integrated Electromyogram
Different Cadences
Knee Extension, et al
Issue Date: 2014
Publisher: 1527-0297
Journal: High Altitude Medicine and Biology 
Abstract: The aim of this study was to determine the influence of severe acute hypoxia on muscle activation during whole body dynamic exercise. Eleven young men performed four incremental cycle ergometer tests to exhaustion breathing normoxic (FIo2=0.21, two tests) or hypoxic gas (FIo2=0.108, two tests). Surface electromyography (EMG) activities of rectus femoris (RF), vastus medialis (VL), vastus lateralis (VL), and biceps femoris (BF) were recorded. The two normoxic and the two hypoxic tests were averaged to reduce EMG variability. Peak Vo2 was 34% lower in hypoxia than in normoxia (p<0.05). The EMG root mean square (RMS) increased with exercise intensity in all muscles (p<0.05), with greater effect in hypoxia than in normoxia in the RF and VM (p<0.05), and a similar trend in VL (p=0.10). At the same relative intensity, the RMS was greater in normoxia than in hypoxia in RF, VL, and BF (p<0.05), with a similar trend in VM (p=0.08). Median frequency increased with exercise intensity (p<0.05), and was higher in hypoxia than in normoxia in VL (p<0.05). Muscle contraction burst duration increased with exercise intensity in VM and VL (p<0.05), without clear effects of FIo2. No significant FIo2 effects on frequency domain indices were observed when compared at the same relative intensity. In conclusion, muscle activation during whole body exercise increases almost linearly with exercise intensity, following a muscle-specific pattern, which is adjusted depending on the FIo2 and the relative intensity of exercise. Both VL and VM are increasingly involved in power output generation with the increase of intensity and the reduction in FIo2.
ISSN: 1527-0297
DOI: 10.1089/ham.2014.1027
Source: High Altitude Medicine & Biology[ISSN 1527-0297],v. 15 (4), p. 472-482
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