​Beneficial Metabolic Adaptations Due to Endurance Exercise Training In The Fasted State

Beneficial Metabolic Adaptations Due to Endurance Exercise Training In The Fasted State

It appears that glucose ingestion during exercise significantly blunts exercise-induced changes in mRNA content in important components involved in fat metabolism. Fasted state exercise has become a popular topic of discussion, which is described as low circulating insulin levels in regards to increased plasma concentration. Also proposed is that fasted exercise stimulates rate of adipose tissue lipolysis, in addition to peripheral beta-oxidation. The current investigation aimed to measure the effects of fasted exercise on body composition, fiber type and endurance performance parameters. A secondary aim was compare a fasted state group and CHO group, which ingested a CHO solution during exercise.


Twenty active male individuals participated in a 6-weekendurance exercise regiment, consisting of a fasted state group (F) and a group who ingested similar amounts of CHO before and during exercise (CHO). Data was collected before and after exercise protocol on several variables on body composition and endurance related performances. The only significant difference between the groups was observed in FATmax which was the estimated exercise intensity required for an optimal rate of fat oxidation. Both groups saw a significant difference from Pre to Post, in VO2, VCO2, RER, Fat Oxidation Rate and Carbohydrate Oxidation.


Further analysis showed intramyocellular lipid (IMCL) content, was significantly different for type I fibers between F and CHO, F significantly increased from Pre to Post as well. When assessing type II fibers, there was a significant difference between F and CHO groups Post exercise. In parameters like GLUT-4 and Capillary Density for both fiber types, both groups presented significant differences. Concerns may arise in the analysis of the glycogen content during a 2hr constant-load about. Only the F group demonstrated a significant difference from CHO after the bout of exercise but not for the net breakdown that occurred. This may have skewed results due to the fact these individuals previously participated in sports activity 4 times per week and were instructed to cease all strenuous activity outside of prescribed regiment. Due to the nature of their respective sports, which could range from endurance to maximal intensity bouts and decrease in exercise frequency, could have impacted the validity of this experiment. Assessment into the fiber type adaptions may also have been impacted due to the previous neuromuscular adaptations of these subjects.

Additional considerations may have been taken in regards to exercise frequency and mode, to direct ultimate aim of the investigation. Incorporating a more directly targeted population such as endurance cyclist may have provided more reliable data on the selected parameters. Selected dietary and conceptual framework of the training regiment provided great standardization to methods. Which is parallel to eliminating initial differences between groups, which was also accomplished through two familiarization events. Strong and effective criteria for analysis were selected to reliably measure the acute and chronic effects of fasted state exercise and possible effects of CHO ingestion during exercise.


Parallel with previous research, it seems fasted endurance does not necessarily increase endurance performance, but may promote beta-oxidation, maintaining ATP production via glycogenolysis. Investigation into varying exercise modes, such as higher intensity interval training could be beneficial to assess specific populations utilizing related exercise protocols. Also investigation could be needed in individuals with diabetic conditions, in relation to the theorized decrease availability of blood glucose, which may have an impact on these individuals.

Zak BrennanComment