It's OK to fail sometimes.

When I come into a workout and feel I don't have enough in the take, I will take in whatever calories I think I need to complete the workout as planned.
If I can't do the workout, I look at how much work I've done and possibly re-evaluate what I'm capable of completing.

High hr is usually dehydration.

Do you weigh yourself daily? I do specifically to track hydration status. If you aren't actively in a caloric deficit, any change in weight is mostly hydration.

You can also check urine color, and do the skin pinch and scratch tests.

Skin pinch test : pinch a fold of skin on the back of your hand. When you let go the fold should immediately return to flat/normal. If it holds the pinched shape for more than 1s you are dehydrated.

Skin scratch test: use your fingernail to scratch the skin on the back of your hand. If it leaves a white scratch mark you are dehydrated. .

High RPE in your case was probably low blood sugar. It can also be excess fatigue, or depleted glycogen. Fatigue usually causes low hr with high RPE.

Answering the glycogen question would need more info about the workouts in the days prior. But, glycogen is replenished by normal diet in 36-48 hours.

Cinnamon roll is kind of a bad choice for pre-workout food...lots of fats, and complex carbs that will just sit in your intestines waiting for enzymes to convert the starch to glucose....it wont do your blood sugar any good in 15minutes. Once you dig into the intervals your digestion will shut down due to lack of blood flow.

Anything that is basically pure sugar would have been ideal. 1/4 cup of sugar 1/4 tsp salt in a standard 20oz bottle of water would have been more effective in the 15 minutes prior.

Consider a ‘too little recovery’ fail also.

If I get into an interval workout and clearly realize it's not going to go to plan, I will often bail on the intervals and just convert to a z2 ride of equal duration. During the z2 ride, I'll try amd assess reason for failure... And preplan accordingly.

Eg, get some food and focus on hydration and perhaps push the intervals to tomorrow or something. I usually have a few scheduling options built into my week to accommodate these events.

If I can get through the first interval ok...and, just feel a little off.... Then I will back down the intensity a few percent and try and complete otherwise as planned. I might bag the last interval, if I feel like crap at that point.

True. But, For me... That manifests as a low hr. And there are usually strong indicators in rhr.

I am leaning “both”. Pee color later had a bit to be desired. And as someone posted above a quite poor choice in food beforehand. The workout effectively stopping digestion of anything that complex.

As for fatigue, usually I classically have lower HR and the heavy legs if that. Thursday was 3x 8min of 30/30’s and off Friday.

I did bail after the one set and just finished the hour with z2 and cooldown.

It happens. Will setup for success next time. Just a good reminder also for races that I may need to put out efforts a similar time of day. Hmmm. Maybe I should on purpose do these that time of day to get it right before having to at race.

Yeah. I have the same issue... In that I prefer to do my hard workouts in the afternoon/evening... So, two meals into the day, and glucose is good and topped off.

Likewise, I have worked out a pre-race routine to ensure I'm well fed prior to early morning race starts. But, I don't like to do it very often.... I'm NOT a morning person.

And shows how individual this is. I do almost all my training in the AM, I am horrendous in the afternoon. Whilst I can do a recovery ride in the PM, even a recovery pace 8-10km jog will have me huffing and puffing and feeling very drained.

In the morning then I'll have toast and honey 15mins before. And then if longer than an hour I'll use some gels/chomps as I go.

But then I'm a hobbit in terms of food - I'll have at least 3 rounds of breakfasts in the AM (5am, 7:30/8am straight after training, and then something 9-10am), a normal human lunch of sarnie/salad/wrap, but I normally don't get too hungry in an afternoon/evening. I do eat properly (pasta, etc) on a night, but on the odd occasions work gets in the way or I'm travelling and CBA then a slice of toast is enough to satisfy.