Thanks for writing in with your question. I don’t recall that part of the conversation.
I think there is some kind of misunderstanding. I am not sure what you mean when you say same %age of HR. Is that % of max HR, AeT HR or AnT HR? We almost never refer to % of any HR so this seems strange that I would have used that term.
The metabolic load would have more to do with running economy and aerobic development than it would with age. Forget age: If runner A is above his/her personal AeT HR the metabolic load will be quite different than runner B who is below her AeT H.R If both runners had similar economy the neuro-muscular loading would have more to do with the pace than the metabolic state.
Can you send me Scott@uphillathlete.com the approximate time in the podcast I will take a listen and reply with a more detailed answer here in the forum.