Thanks for your great questions. Yes as ever with nutrition there is always a lot of information/research surrounding the topic, and context is king when it comes to application.
I’m going to attempt to answer your questions and I’ve asked Scott to step in and help, so hopefully we can have his input.
As we tried to highlight in the podcast regardless of dietary intake simply carrying out endurance training per se, at the lower intensity heart rate zones, increases our bodies ability to utilise fat as a fuel source (fat adaptation). There is limited data to show that carrying out fasted training translates into superior performance benefits. However both Scott and myself have observed when those who do carry out fasted training appropriately, this person sees benefits to their training in terms of; can start to go further over time without eating during their fasted run, reduce desire to eat on non fasted low intensity runs, reduce cravings for carbohydrate/sugary foods. So potentially yes you could reap greater benefits in a short space of time but this will also depend on the training status of the individual. I’m not sure there is a ‘lipid preferential’ zone during the day. The lipid preferential state will come from the intensity of the training session i.e. zones 1 & 2 low intensity and potentially you can influence this state via carrying out the training session a fasted state and manipulation of dietary intake.
Generally if you were simply carry out a recovery session fasted, this is not going to create a higher state of stress. I would assume the recovery session was of low intensity and for a short duration? Depending also on the time of day (which I again assume was first thing in the morning prior to breakfast) at this time your muscles are still going to contain a source of glycogen. It is the low/depleted glycogen levels in the exercising muscles that have a greater influence on the increased stress response (again assuming you are not on a low carbohydrate/keto diet and ate carbohydrate in your recovery meals post exercise the day before).
I will let Scott answer this final part of your question in terms of carrying out a strength based session later in the day after a fasted session.
Question 3) I’ve not heard of this myth so will let Scott answer this question. However it sounds like a myth as when training for the mountains / ultra endurance you need to train both energy systems (aerobic and anaerobic) and get strength to support your efforts of your objective. You will just need to be strategic about this training.
I hope thats be of help?