Level 9 Valued Member
But at the end of the day almost all serious endurance folks do the majority (not all) of their yearly training using LED. Success leaves tracks.The only real difference is a slight advantage to capillary density goes to LISS, and its not clear if that advantage decreases over time - some studies don't even back that up. Stroke volume, stroke pressure, hypertrophy, blood volume increase, mitochondrial density, aerobic enzyme improvement, fat mobilization, glucose mobilization etc etc are all roughly equal, with HIIT increasing mitochondrial density somewhat better in the region of type II fibers. They use different pathways to achieve 90% similar outcome. As you become more advanced, LISS confers more benefit, but still requires a lot of training time.
And again, if you want to run better, you absolutely have to run. There are examples of people using HIIT to do half marathons and under and do well enough. For a full marathon I don't think anybody uses it exclusively. I did read about one man who did so experimentally and his time was over 3 1/2 hours - he did finish though.
(And marathons are pretty short in the world of locomotive endurance… )