Urskogen
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35
Johanneshov
Hjälte
301 inlägg
2010-03-28 10:12
en korsbryggecykel i en muskel drar lika mycket energi innan som efter frukost.
För den som är intresserad av energisubstrat kommer här ett (tyvärr inte extremt detaljerat) utdrag ur Medical Physiology (Boron & Boulpaep, Saunders Elssevier). Värt att påpeka är att oavsett om muskeln använder fett eller glukos som energisubstrat är det som folk redan sagt energimängden
enbart som avgör åt vilket håll vikten rör sig, eftersom man ändå kommer att använda energin i frukosten till det arbete man utfört, oavsett om man äter innan eller efter. Skillnaden blir bara att man "köper på kredit" när man använder förråden vid träning innan frukost och man kommer betala igen det när man äter.
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For sustained activity of moderate intensity, fat is the preferred substrate, given ample O2 availability. For example, at 50% of VO2max, fatty acid oxidation accounts for more than half of muscle energy production, and glucose accounts for the remainder. As the duration of exercise further lengthens, fatty acid oxidation progressively increases, and it becomes the dominant oxidative fuel as glucose utilization by the muscle declines. However, as exercise intensity increases, active muscle relies increasingly on glucose derived from intramuscular glycogen as well as on blood-borne glucose. This crossover from lipid to carbohydrate metabolism has the advantage that, per liter of O2 consumed, carbohydrate provides slightly more energy than lipid. Conversely, as muscle depletes its glycogen stores, it loses its ability to consume O2 at high rates.
At a given metabolic demand, the increased availability and utilization of fatty acids translate to lower rates of glucose oxidation and muscle glycogenolysis, thereby prolonging the ability to sustain activity. Endurance training promotes these adaptations of skeletal muscle. Under conditions of carbohydrate deprivation (e.g., starvation), extremely prolonged exercise (e.g., ultramarathon), and impaired glucose utilization (e.g., diabetes), muscle can also oxidize ketone bodies as their plasma levels rise. <<<
blarrgh!
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