Hi Fascat! My partner does a lot of her trainer rides at night and often has trouble holding her cadence on hard intervals. It’s true that at night you are low on glycogen and doing hard intervals should be done earlier in the day, correct? Thanks!!
Hey @daniel.kessler - honestly everyone is different. I know many athletes that enjoy training in the evening. But for me, I always aim to do my harder intervals in the morning as that is when I feel the strongest. If she is eating carbs throughout the day and not doing intense physical activity, her glycogen stores should be fine. I would recommend she try to train in the morning and see if she feels like the sessions are more doable.
Also important to note that her cycle could impact her ability to hit hard intervals. During the high hormone phase (around mid week 3 and into week 4 of the menstrual cycle), females typically experience greater fatigue which often increases over the course of the day… along with quite a few other physiological changes that make high intensity efforts tough.
You can read more on that in this thread I posted in a while back 
Thank you for the useful information!
Is it OK that sometimes I kust cannot do stuff I did before? It happens that on some day my strength simply disappears, and this state lasts for several days. I noticed that this is not related to the menstrual cycle - it happens for some unknown reason. I would like to know if anyone else has experienced something similar. Thanks