Hello! I was reading UA’s latest blog post on the physiology of aerobic base training (https://uphillathlete.com/aerobic-training/science-and-physiology-of-endurance-training/?utm_source=mailchimp&utm_medium=emails&utm_campaign=May172023-newsletter), and I had a question: does the “lactate shuttle” part of the aerobic energy pathway ever become the limiting factor of aerobic performance? In other words, is there a point in which the mitochondrial density of your slow twitch muscle fibers (in which training below your aerobic threshold improves) aren’t being fully utilized, and the bottle neck of your aerobic energy system is the speed/efficiency in which the molecules can transport lactate to the mitochondria dense slow twitch fibers (this efficiency which can be trained by training near your lactate threshold, but is also largely based on genetics)?

Thanks so much for your insight – the article was super helpful in understanding some of the science beyond all this Z1/Z2 training I’ve been doing! And if I got anything wrong in my questions above, please correct me!