Why do I get tired in less then a minute when sparring If train real hard?

[SthPaw]

Nothing really to add that hasn't been said to be honest, but pretty much every response here has been good advice.

I used to have the same issue when I was just starting out. I could skip for long time, hit the bag round after round and feel fine, run my miles etc...but in sparring I would be gassed inside the first minute. As people said, it is nerves/adrenaline/breathing control. The more you do it the more you will be used to holding yourself comfortably. Trust me I've been there too!

[DinoCop]

Because you are under stress and cannot control it. During bag and shadowboxing noone is controlling you, you are shotting at will. During shadowboxing your imaginary enemy attacks you whenever you want and you breath out or in good.
I remember I beat myself when I get in the ring for the first time, I beat myself with breathing. It took 15 second before I got out of fuel.

[AddiX]

Rpvi hit it right on the head. When someone else is controlling when and how you move your body can only prepare so much for it.

Fight someone who is better than you, your tired in 1 rnd, fight someone your much better than, you can go 4-5 easily.

Also adrenaline.

And this sounds stupid, but a lot of beginners actually forget to breath because of how nervous they are.

[nivek535]

nervous
tense
not breathing right

[Amazinger]

When it comes to hitting the punching bag, double end ball and shadow boxing I can do 8 to 10 rounds with good intensity and I don’t get tired but when I get in the ring to do sparring my arms and legs feel very heavy with no energy, slow and I get tired in less then a minute, so I receive a lot of punches and feel powerless. I also do 30 min of roadwork or 45 min of stationary bike so I don't know what is wrong. Can someone please tell what could I do to improve?

When you do roadwork or cardio. Do you get to the peak heart rate?. One must reach the peak to get to the next level in cardio.

If you stopped running before you even peaked heartbeat(exhausted)then the run is almost worthless to your need (only calorie burning).

[Equilibrium]

Because you are nervous when you get in the ring most likely, chill out it's just sparring.