>biked 80km yesterday >barely going 10km/h by the end >slept

No matter how gud you are, the human body only has enough readily glycogen for about 2.5 hours effort before your energy level falls off a cliff. For rides you expect to take longer than that you need to start eating by about 1.5 - 2 hours in to head off the collapse since it will take your body 30 - 40 minutes to convert that food into a usable form.

Also hydration because dehydration has similar symptoms, though the recovery is faster.

>>1092160
Cycling doesn't get easier, you get quicker.
Need to start hydrating at least by 20 mins into ride. Feeding within 30mins. Practice makes it better.

>>1092160
Nobody said it'd be easy

>>1092168
You mean, that taking breaks every two hours would let your body produce fresh glycogen supply?