. i'm trying to find a good balance of fat/carbs/protein, but when looking back on the calorie-counting app that i'm tracking my diet with, i've dropped my daily carb intake significantly (down to about 20-25% of my total daily calories were from carbs). i tried to increase this lately, to anywhere from 40-50% of my daily intake, and my legs feel like brand new... although i still get the occasional day where they just don't feel right.
The scientific consensus is that ideally you need 7-10 g/kg/day of carbs if you are engaged in intense training. Go lower than 5 and your endurance performance will suffer.