[masraum]

Originally Posted by zakthor

I think this is true but I think another word for it is "aerobic fitness." I haven't seen any evidence that riding fasted helps grow aerobic fitness. It hurts so I wanted to think there was a benefit but I've found no science that agrees. Supposedly peak benefit to aerobic fitness comes from riding at low intensity (Z2) for between 2.5-6 hours and no one's found a shortcut.

I have two friends that are competitive in the local 100 mile mtb races. They both look like birds, both are really fast, and they both have put in a lot of training hours over the last 10-15 years. Both independently started screwing around with keto diet and both lasted 9-10 months before deciding it was too difficult and took too much happiness from their lives. They did it just long enough to catch up to their old pre-keto speed, then gave up. They said they were unable to hammer when they were on the keto diet, but they also didn't need to eat all day long.

After years of high level competition and structured training they are still both very conscious about diet, they get most of their off bike calories from fat and protein, but on the bike they hoover up nasty chemical carb packs like they are hummingbirds.

The aerobic process needs blood sugar to operate, if the blood sugar drops you bonk and the body starts metabolizing muscle. Even endurance mtb races have high intensity and you'll eventually deplete all your sugar stores, I don't know anyone that doesn't eat carbs during a race to try and replenish their stores. At the most I can take in 350-400 calories/hour of simple sugar.

Anyway, that's my sample. The best diet book I found is "Advanced Sports Nutrition" by Bernardot, is the only book that really connected the dots for me.

If you've got some science to share about fasted training I'm all ears.

Fasting and keto (ultra low carbs, ie Atkins) are different, even if you do get into ketosis.