is discussed in the previous chapter and will not be reproduced here. To briefly recap, the
increased rate of lactate production during interval training overwhelms the body’s ability to
buffer or reuse the lactate and there will be a build-up of lactate in the bloodstream.
Section 4: Fatigue during interval training
and the effects of a ketogenic dietAs stated, during exercise above lactate threshold, anaerobic glycolysis leads to a
generation of lactic acid. During high intensity exercise of 20-60 seconds duration, lactic acid
accumulation is the most likely cause of fatigue (13,14). At fatigue, glycogen levels in the muscle
fibers typically remain high (15,16) further suggesting that fatigue is occurring from the buildup
of waste products. Thus, it would not appear that a ketogenic diet would directly impair
performance during this type of exercise as glycogen availability is not the limiting factor. During
repeated bouts of high intensity exercise (i.e. sprint training), depletion of glycogen will become an
important factor in fatigue (17).
The effects of glycogen depletion during interval sprint exercise has been thoroughly
studied. Most studies (18-24) have reported a decrease in exercise performance during sprint
training (at various intensities above LT). The reason for the drop in performance is not
immediately apparent.
While on a ketogenic diet, although pH is rapidly normalized, there is a decrease in the
body’s buffering capacity due to lower bicarbonate levels (19,20,21,25). Since bicarbonate is used
to buffer the lactic acid produced from anaerobic glycolysis, fatigue during a single interval may
occur faster due to greater lactic acid buildup in the muscle.
This link between blood pH and sprint performance is not supported by at least two
studies. Following 5 days of a ketogenic diet, lactate levels do not differ during sprint exercise (20)
which indicates no impairment in glycolysis. Additionally, reversal of the acidosis by bicarbonate
ingestion (23) did not improve performance in the ketogenic diet group.
Another possible cause of fatigue is a decrease in the muscle’s capacity to generate energy
through anaerobic glycolysis. The major regulating enzyme of glycolysis (called phosphorylase)
breaks stored glycogen down to glucose for the cell to use. Phosphorylase activity decreases
when glycogen levels fall below a certain level (about 40 mmol/kg) and this may be a cause of
muscular fatigue (24, 26,27).
Indirectly supporting this idea are studies examining the effects of higher than normal
glycogen levels on performance and glucose use. It appears that glycogen supercompensation
above normal does not increase glycolysis (27-29) compared to normal glycogen levels. Thus, as
long as glycogen is above a certain level (40 mmol/kg), glycolysis is not affected. Only when
glycogen falls below a certain critical level does performance suffer.