VO2Max: "The highest rate of oxygen consumption attainable during maximal or exhaustive exercise" (Wilmore & Costill, 2007). This is a rough measure of fitness.
Both groups started out with levels around 3.5 liters per minute (l/min), which is close to standards for untrained individuals. To put this into perspective, elite endurance athletes have about twice that capacity. One Norwegian skier topped this chart at 7.3 l/min. A more accurate measure of VO2Max is ml/min/kg, but in this study l/min was noted.
Fasted: +9.7% increase
Fed: +2.5% increase
The fasted group increased their VO2Max significantly more than the fed group. Interesting.
It's also noted that "Whilst peak power increased in both groups, there was a strong tendency for FAST to improve their peak power more than FED".
Muscle glycogen content: This is measured in millimoles per kilo dry muscle and shows how much glucose is stored in the muscle. The sample was taken from vastus lateralis, a portion of the quads, since this was the main muscle exercised during the cycling sessions.
Fasted: +54.7% increase
Fed: +2.9% increase
As you can see, the fasted group showed a dramatic increase in muscle glycogen content compared to the fed group. It's almost too good to be true.
Citrate synthase (CS): This enzyme is critical for the initiation of the citric acid cycle, which regulates the mobilization of fat and converts glycogen into glucose for use during exercise. Think of it as a marker for fuel utilization efficiency.
Fasted: +17.9% increase
Fed: +19.1% increase
While the differences between groups, on average, did not show any significant differences, these appeared when comparing the results obtained from the women with those of the men. When this comparison was made, fasted training was found to stimulate significantly greater increases in CS in men (+35%) than in women (+10%).
On the other hand, fed training stimulated significantly greater increases in women (+25%) than men (+10%).
Men attained a more much better response from fasted training, while women received a more favorable response from fed training.
3-hydroxy-CoA dehydrogenase (HAD): Also a marker for fuel utilization efficiency, but this one is specifically involved in fatty acid metabolism. Think of it as a fat burning enzyme.
Fasted: +3.5% increase
Fed: +9.1% increase
As was the case with CS, the mean increase above is a bit misleading, since there were big differences in between fasted and fed groups depending on gender.
When looking at gender differences, females showed a stronger response than males (+5% fasted and +25% fed). This goes in line with prior studies which show that the HAD activity of female muscle is more responsive to the same training stimulus. Males in both groups showed only subtle change that was deemed non-significant (+3% fasted and -10% fed). However, fasted training seems to provide a slight edge once again.