I can't go a week without someone cornering me or sending me the latest “study” about the benefits of high intensity training. And more specifically high intensity every workout while cutting out endurance training. The tricky part is athletes don't compete in labs, they compete in the real world, in varying conditions, in multiple time zones, after sometimes days of travel.
Endurance training, lets say 4-6 hour rides(skis, snowshoes etc) helps build that athletic areobic foundation. It aids in recovery time, and dealing with ongoing stress. It helps you get to the start line of a race, ready to race. Not bagged and ready for bed after all the preparation that goes into racing.
Point 1) I'll use some of my younger athletes first visit to the Tremblant Canada Cup as an example. (i owe you guys 20 pushups) For many of them it was their first out of province, (heck out of the GTA) bike race. They faced a 7-8 hour drive, sleeping in a hotel, eating on the road, a crazy venue, a crazy course to pre-ride both climbing and technically. All firsts, all adding to their fatigue levels. I'll be honest by the time they arrived at the start line, they were tired. I knew they would be, but it was still an amazing experience for them and they learned a TON. A big limiting factor for that weekend as a whole was their aerobic base, not their intensity, or speed, or climbing, or tech riding.
Key words limiting factor for the weekend, not the race. If all the cadets and juniors woke up at their houses and raced on Zwift that day, I bet the times would be a lot closer. It takes a lot of energy just to prepare for a race, and if you don't have a good base in place you won't be recovered enough to hit your peak in the race.
Point 2) Athletes and coaches aren't stupid(welll.....), coaches have tried this tactic before cut waaay back on volume and increase intensity. It rarely works in the long term, dealing with 50 hour travel days through volcanic ash clouds, to China, to South Africa, NZ , OZ, it takes its toll. Its like its own stage race before the race. Sure you can be fit, fast, ready to rock for the duration of your race, (or lab test ;) but are you ready for a road trip, dealing with road food, sleeping in weird places, not sleeping on a plane and then rolling to the line rested and ready to perform. How does an athlete only doing HIT all year, every week prepare for that long term chaos?
I don't dispute the outcomes of these studies, I have very little doubt that a lot of intensity will lead to some big gains in fitness. But coaching and being an athlete is ALL about sacrifice, balance and compromise. We don't live in labs, not to say we can't learn from studies from researchers and universities but I encourage my athletes and my peers to take a holistic approach to training, racing and life as its all connected.