michelbrazeau said:....The question I have, is that since SST training is mostly in the range of 75-95% of threshold, most likely the primary source of energy is from muscle glycogen, as at that intensity, the demand is too high to metabolize fat....
Sugars are the primary fuel source during SST and higher work, but you'll still burn quite a bit of fat when working SST. I've done four and five hour rides that averaged to high Tempo/low SST. The calories burned were far more than what 1500-1800 Calories of stored glycogen and what I ate along the ride could account for. And no I didn't bonk on those rides. You don't completely switch to sugars for fuel in the intensity range described by SST training.
Quoted post said:...In my case, I found that during long races 3+ hours, I am depleting my glycogen reserves, ...I'm getting the impression that this is because I have done too much of my training in sweet spot, and not enough at lower intensities....
If you're bonking on longer rides/races it's because you're depleting your glycogen/blood glucose stores. The only answer to that is to: make sure your glycogen stores are topped up before events(critical half hour refueling on previous days is key here), consume enough carbs during the ride itself, and ride your events at an intensity that allows you to burn some fat when you can.
That last part basically translates to getting your sustainable power high enough that you're not pressed right to your limits too often during long races. IOW, high FTP leads to endurance because in addition to having the power needed during sustained crunch times(like long climbs) you can ride at a lower relative percentage of your FTP for more of the race(most of your pack time should be Tempo or below). Working at a lower percentage allows you to burn more fats and preserve more of that precious glycogen.
The only link I've seen to lower intensity rides leading to more endurance is that it can marginally improve your ability to store glycogen. But we're talking about the difference between storing say 1600 Calories and 1800 Calories depending on bodyweight and gender. That's not enough difference to carry you if you're having to race a long event right up against your FTP. I've never seen any research, studies or reviewed sports science that supports the idea that you can "teach" your body to preferentially burn fats with long easy work. Sure that idea surfaces frequently on forums like these and some coaches swear by it, but do a Pubmed search or dig into some reputable sports nutrition books and see what you find. Endurance comes from proper fueling and training that raises your sustainable power, not by "training" your body to prefer fats at moderate to high intensity.
Long rides make sense for getting used to being in the saddle, to dial your feeding and hydration strategies, to work on pacing longer events, and to a small extent to encourage greater glycogen storage. They can also be a great way to build CTL and long term training load also contributes to endurance. But as much as I hear folks talk about it I haven't seen a single peer reviewed piece of research that supports the idea of teaching your body to preferentially burn fats at higher intensities. You want more endurance, train for more sustainable power....
-Dave
