Thanks to Luis at Ketogains for pointing to a great study which looks at the studies of Glycogen and Exercise (Pim Knuiman, Maria T. E. Hopman, and Marco Mensink. Glycogen availability and skeletal muscle adaptations with endurance and resistance exercise. Nutr Metab (Lond). 2015; 12: 59.).
…Recent research into the effects of glycogen availability sheds new light on the role of the widely accepted energy source for adenosine triphosphate (ATP) resynthesis during endurance exercise.
Indeed, several studies showed that endurance training with low glycogen availability leads to similar and sometimes even better adaptations and performance compared to performing endurance training sessions with replenished glycogen stores.
The study leads with:
…Glycogen is made and stored in cells of the liver (~100 g) and muscles (~350 – 700 g; depending on training status, diet, muscle fibre type composition, sex and bodyweight) and can be reduced by fasting, low intake of dietary carbohydrates and/or by exercise.
Intermittent Fasting, Low Carbs, exercise. Yep, that’s me.
Glycogen is differently distributed within the muscle fibers (subsarcolemmal ~5-15 %, intermyofibrillar ~75 % and intramyofibrillar ~5-15 %)
And here’s the bit about high intensity workouts:
Glycogen is an essential substrate during high intensity exercise by providing a mechanism by which adenosine tri phosphate (ATP) can be resynthesized from adenosine diphosphate (ADP) and phosphate.
The relative use of energy sources during exercise is mainly determined by the intensity and the duration of the exercise bout, as well as the athlete’s training status.
Fat as source of energy is relatively most dominant during moderate intensity (30-65 % of VO2peak), whereas the relative contribution of carbohydrate oxidation to total energy expenditure becomes greater when exercise intensity increases, with muscle glycogen becoming the most important substrate source
…glycogen availability is essential to power ATP resynthesis during high intensity exercise which relies heavily on glycogenolysis.
Furthermore, it has been well documented that the capability of skeletal muscle to exercise is impaired when the glycogen store is reduced to a certain level, even when there is sufficient amount of other fuels available.
To date, few studies have found an improved training-induced performance effect of conducting the exercise bouts with low glycogen levels compared with replenished glycogen levels
On the subject of resistance training:
… a typical resistance exercise session has been shown to reduce glycogen levels by approximately ~24-40 %. This reduction in glycogen content during exercise is determined by the duration, intensity and volume of the performed exercise bout. The largest reductions in glycogen are seen with high repetitions with moderate load training, an effect that mainly occurs in type II fibers.
Remember glycogen is the storage form of glucose.