Section 5: Effects of the Ketogenic Diet
on Weight TrainingRelatively few studies have examined the effects of carbohydrate depletion on resistance
training. Typically, researchers measure maximal force production during a single isometric
contraction or muscular endurance during multiple rep sets during isokinetic exercise. Isokinetic
exercise machines are special types of weight training equipment that control speed of
movement. They are typically not found outside the laboratory and may not be an applicable
model to normal strength training.
As a general rule, the maximum amount of force generated ultimately depends on Type II
muscle fibers while muscular endurance depends more on Type I fibers. The effects of glycogen
depletion on force production is fiber type specific. Glycogen depletion of only Type I fibers does
not impair maximum force but decreases muscular endurance as would be expected (109,110).
Glycogen depletion in both Type I and Type II fibers causes a decrease in both maximal force
production and muscular endurance (109). In contrast, one study found that depleting both
muscle fiber types of glycogen to approximately 40 mmol/kg did not cause a decrease in force
production or muscular endurance (111).
It is difficult to draw conclusions with regards to strength training from these studies as
performance was only measured during a single set. Multiple sets of weight training are much
more likely to be affected by glycogen availability. As discussed in the section on interval
training, glycolysis may be impaired when glycogen levels fall below a critical level (40 mmol/kg).
Although data on strength training is lacking to verify or deny this concept, many individuals
report fatigue during weight training sessions performed later in the week, so something is
occurring.
Not all lifters report this occurrence though so it may simply be individual, related to the
total amount of training done during the week. Individuals who perform a high volume of training
(number of sets) during the early part of the week tend to report a drop in performance compared
to those who do not. This suggests that the fatigue is local (i.e. glycogen depletion, dehydration,
potassium loss) rather than systemic (i.e. changes in blood pH) as discussed in section 4.
Long term ketogenic diet and high intensity activity
At this time, only one study (112) has examined high intensity exercise performance after
long term adaptation to a ketogenic diet, finding no decrease in performance. As performance at
higher intensities are generally determined by non-oxidative metabolism, it seems unlikely that
long term adaptation to a ketogenic diet would have an effect on exercise of this type. Since no
research on this topic exists, any long term effects on performance are purely speculative at this
time. The main determinant in performance in weight training is probably muscle glycogen
levels. Thus, the amount of work that can be performed in a given workout will depend on
starting muscle glycogen levels.