[A.Steinbach]

Bild från Exercise Biochemistry Vassilis Mougios 2006

Här ovan kan man se att anaerob återsyntetisering av ATP från muskelglykogen är relativt hög och är därför av största vikt vid tempoökningar eller spurter i tävlingsammanhang. Även aerob återsyntetisering av muskelglykogen ligger högre än både IMTG och TG.

Vikten av att kunna utvinna energi anaerobt/aerobt ur glykogen är extremt viktigt för att kunna prestera maximalt och det har visats att förmågan att utvinna energi ur glykogen minskar om man äter en lågkolhydrat- högfettkost även om det finns glykogen tillgängligt. En av anledningarna verkar vara påverkan på PDH men det lär ju även vara enzymer involverade i glykolysen som nedregleras vilket leder till att högintensiv aktivtet blir lidande. Alltså att bli "fettanpassad" leder till oförmåga att utvinna ATP snabbt ur glykogen för att kunna bibehålla högintensiv träning.

There are indications that the price paid for such extreme conservation of carbohydrate during exercise appears to be a limitation on the intensity of exercise that can be performed. Although resting muscle glycogen and blood glucose levels were normal at [week 4], at [week 3, when VO2max was also tested] there was a marked attenuation of the RQ value at VO2 max, suggesting a severe restriction on the ability of subjects to do anaerobic work. This does not appear to be a function of differential accretion of glycogen by different fiber types, as the muscle biopsy specimens obtained before exercise showed the fast twitch fibers to be qualitatively replete with glycogen at [week 4]. Thus, the controlling factor does not appear to be the presence or absence of substrate within the fiber. Rather it is more likely a restriction of substrate mobilization or fiber recruitment. The result, in any case, is a throttling of function near VO2max, apparently by limitation of carbohydrate utilization. This appears to occur in exchange for a more ready use of fatty acids at moderate submaximal power levels, ie, at or below 65% of VO2max

Metabolism. 1983 Aug; 32 (8): 769-776. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation

It is concluded that ingesting a fat-rich diet during an endurance training programme is detrimental to improvement in endurance. This is not due to a simple lack of carbohydrate fuel, but rather to suboptimal adaptations that are not remedied by short-term increased carbohydrate availability.

Interaction of training and diet on metabolism and endurance during exercise in man
Journal of Physiology (1996), 492.1, pp.293-306

In conclusion, the HFD-CHO dietary strategy increased fat oxidation, but compromised high intensity sprint performance, possibly by increased sympathetic activation or altered contractile function.

Fat adaptation followed by carbohydrate loading compromises high-intensity sprint performance
J Appl Physiol 100: 194–202, 2006

The main conclusions of this study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced
muscle glycogen store and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system at rest and after exercise.

The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise
Eur J Appl Physiol (1997) 76: 128-133

However, there is now evidence that what was initially viewed as “glycogen sparing” after adaptations to a fat-rich diet may be, in fact, a downregulation of carbohydrate metabolism or “glycogen impairment.” One study (12) has reported that fat adaptation/carbohydrate restoration strategies are associated with a reduction in the activity of pyruvate dehydrogenase; this change would act to impair rates of glycogenolysis at a time when muscle carbohydrate requirements are high. The present study of Havemann et al. (6) furthers our knowledge by applying the fat adaptation/carbohydrate restoration model to an endurance cycling protocol that involves several features of a real-life race: self-pacing and the interspersing of highintensity bouts of cycling with more moderate-intensity segments. The results show that the dietary strategy has no effect on overall performance of a 100-km time trial but compromises the ability of well-trained cyclists to performance high-intensity
sprints.

“Fat adaptation” for athletic performance: the nail in the coffin?
J Appl Physiol 100: 7–8, 2006;