*3.1. Skeletal Muscle Adaptation*

Of the studies examining the e ffects of longer-term (>4 weeks) training in the fasted state on endurance adaptations [12–14,143–145], only one [144] has used endurance-trained subjects. Furthermore, almost all studies using moderate-intensity continuous endurance training in the fasted state also provided the fed groups with CHO during exercise, which can independently influence both acute [120] and chronic [93] responses to exercise. Other studies have examined pre-exercise CHO supplementation, though not necessarily in the overnight-fasted state and using untrained subjects [146,147]. Additionally, fasted state training has been used as part of studies comparing low vs. high muscle glycogen [148] and once vs. twice daily training [149]. Therefore, making comparisons across studies is challenged by the variety of methods that have been used to compare high vs. low CHO availability around training sessions (Figure 8).

**Figure 8.** Comparison of the various methods of altering CHO availability used in training studies. Protocols used to commence training with a reduced availability of endogenous carbohydrate include overnight fasting, and training twice within a 24 h period consuming low-CHO nutrition between sessions or remaining in the fasted state. Some studies have fed carbohydrate during exercise, while others have not. Thickness of the line is related to the number of studies using a given approach. Question marks represent areas ye<sup>t</sup> to be studied. Created from [12–14,31,35,93,141–145,148–153], which included 307 participants (10.7% female), 26.3 ± 4.2 years, VO2max 53.2 ± 11.0 mL kg−<sup>1</sup> min−1.
