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- Gustafsson, C, et al.
(author)
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Effects of normobaric hypoxic confinement on visual and motor performance
- 1997
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In: Aviation, Space and Environmental Medicine. - 0095-6562 .- 1943-4448. ; 68:11, s. 985-992
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Journal article (peer-reviewed)abstract
- INTRODUCTION: The use of reduced oxygen levels has been suggested for fire prevention in closed spaces, such as submarines. However, if humans are to work and live in environments with reduced oxygen levels, the effect of hypoxia on human performance must be further assessed. METHODS: In 3, 11- to 14-d confinements a total of 22 subjects were exposed to different levels of normobaric hypoxia (13, 14, and 15 kPa O2), for up to 10 d, with intervening periods of normoxia. In each experiment eight subjects were divided into two teams, working in 6-h shifts around the clock. Subjects performed tests of spatial orientation, visual reaction time, parallel processing and motor skills. Performance tests and questionnaires were administered once or twice in every 24-h period. RESULTS: All of the subjects appeared to tolerate the acute reduction in oxygen partial pressure well. In many of the tests performance improved with time as a result of learning, despite reductions in the oxygen level. No reduction in performance or decrease in rate of learning was observed at any of the oxygen levels tested. CONCLUSIONS: Oxygen levels down to 14 kPa appear not to impair visual and motor performance during rest.
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- Kim, Chang, et al.
(author)
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Training effects of electrically induced dynamic contractions in human quadriceps muscle.
- 1995
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In: Aviation, Space and Environmental Medicine. - 0095-6562 .- 1943-4448. ; 66, s. 251-255
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Journal article (peer-reviewed)abstract
- The effects of electrically induced dynamic muscle contractions on muscle endurance, strength, morphology and enzymatic adaptation were studied in seven male physical education students. The training program consisted of electrically induced one-leg extensions on a modified Krogh cycle with a 30-Watt (W) load for 60 min, 3 times a week for 4 weeks. Muscle fiber type composition was unchanged, but diffusional capacity was increased after electromyostimulation training. The endurance capacity in the trained leg increased by 82% (p < 0.01), but there were no significant changes in citrate synthase, phosphofructokinase activities, and carbonic anhydrase III and myoglobin contents, suggesting that neural adaptation and learning were more important factors for the increased endurance capacity than enzymatic adaptation. Prolyl 4-hydroxylase activity, a marker of collagen biosynthesis, increased 3-fold (p < 0.01) as a result of the training. This could be due to muscle damage caused by electrically induced muscle contractions. In conclusion, electrically induced dynamic muscle contractions can increase muscle endurance without clear concominant changes in muscle morphologic and enzymatic adaptation. Increased prolyl 4-hydroxylase activity could suggest muscle damage caused by electrically induced muscle contractions.
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| 4. |
- Mekjavić, I. B., et al.
(author)
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Inhalation rewarming from hypothermia : an evaluation in -20 degrees C simulated field conditions
- 1995
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In: Aviation, Space and Environmental Medicine. - 0095-6562 .- 1943-4448. ; 66:5, s. 424-429
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Journal article (peer-reviewed)abstract
- The present study evaluates the efficacy of inhaling warm moist air as a method of rewarming from hypothermia in -20 degrees C field conditions. The method of inhalation rewarming is compared to two other methods of rewarming: a) passive rewarming; and b) passive rewarming, with a respiratory heat exchanger designed to minimize respiratory heat loss. Eight male subjects were rendered hypothermic by immersion in 15 degrees C water for 1 h. They were withdrawn from the tank earlier, in the event that their rectal temperature (Tre) decreased to 35 degrees C, or by 1.5 degrees C from the pre-immersion value. Upon completion of the immersion, they were placed in a well-insulated sleeping bag assembly and transferred to a cold room maintained at -20 degrees C for a 2 h rewarming period. They participated in 3 trials: Control-passive rewarming; Heat Treat-inhalation rewarming with the Heat Treat; HME-passive rewarming in conjunction with a respiratory heat and moisture exchanger (HME). During the rewarming period, inspired air temperature was -19.4 +/- 1.1 degrees C in the control trial. In the HME and Heat Treat trials subjects breathed via an oro-nasal mask. The inspired air temperature was +20.5 +/- 1.2 degrees C in the HME and +36.2 +/- 2.9 degrees C in the Heat Treat trial. The post-immersion drop in Tre was significant in all conditions. The reduction in the post-exposure drop in Tre observed with the Heat Treat may be attributed to the minimization of respiratory heat loss, since the magnitude of the reduction was similar to that observed with the HME. (ABSTRACT TRUNCATED AT 250 WORDS)
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