I'm not aware of any studies where exercise effects circadian rhythms. Although if it did, I imagine would be because you started working out in times you normally prepare for sleep. So if you went to bed at 10 pm on rest days and midnight on workout days, your body may have a difficult time adjusting to that.
Whether exercise effects your sleep generally depends on how intense the workout (there's intense and there's intense), how much you're overreaching, and just yourself. Everyone acts to stimuli differently.
Exercising in evening could:
Significantly raise your adrenaline and cortisol levels. In which case you'd be tossing in turning for hours trying to bring it down.
Raise your adrenaline, but then you come crashing down hard shortly after. In which case you'll actually sleep quite well.
Do absolutely nothing. You'll get home and just go to sleep as if nothing happened.
The first case is usually a sign that you simply went too hard at the gym. It is also a good indicator that you're overreaching and it may be time to slow down for a week. Oddly, not sleeping can cause you to get in to this state much sooner.
Sleep is very important. It is a vital tool for both weight management and recovery, as well as just overall health and cognizance. So if you must workout at night, here are some tips:
- Put all of the most intense stuff at the beginning of the workout, and then use the rest as a cooldown. Finishing off with some light stretches can help get the heartrate down.
- No preworkout or any kind of drug that's used to give energy (no caffeine basically). This may hurt performance, but not sleeping will most certainly hurt performance.
- Try to keep a consistent sleep cycle.