Sparring is a very strenuous activity, and can be a great workout. It burns a lot of calories and will get you in great shape if you do it often enough. But like any strenuous activity, you have to monitor your energy level very carefully as you will have a drop in performance as you get tired.
One way you can avoid this drop in performance is by being very efficient with your movements. I’ve seen countless students look like they were fighting with their pants of fire, going full energy for the first part of the fight, only to slow down and get crushed the second part of the fight.
To avoid this, you need to meter your energy and movements so that you can go as long as you need. You should never, ever feel at the end of a fight that you have given everything you have. You should always have some reserve, as you never know when you will find yourself on the street, with one more attacker to deal with.
Certainly, you can work out and exercise a lot in addition to your martial arts training, and that will help you with your overall conditioning. Likewise, if you spar often you will build up sparring specific conditioning that will also allow you to go longer without getting as tired. But, regardless of your overall physical condition, efficiency in movement makes sense. It allows you to be more precise in your attack, and develop different cadences while sparring. This allows you to be less predictable to your opponent as you fight, and can help your offense be more effective.
Another aspect to this efficiency is to only throw techniques that you want to strike with or use to setup another technique. Beginner and intermediate students often throw a lot of techniques most of which have little to no chance of striking their opponent. This results in a lot of wasted energy and reduced performance. As you become an advanced practitioner, however, you will tend to throw fewer numbers of techniques at your opponent, but they have a much higher chance of being effective. This efficiency is what you want to strive for.
So, as you are practicing your sparring in class, think about your offense and try to only strike when you think it has a good chance of connecting. Don’t just throw kicks and punches for the sake of throwing kicks and punches. This isn’t to say you shouldn’t throw a lot of them, as the only way to strike your partner is to throw a technique. But, your goal is to be efficient with your strikes. It will help you become a more effective fighter.