Swim sprints:
It's a 20 minute program. Once it starts it's over in 20 minutes. The object of this is to train your body to recover from full blown exhaustion in 30 seconds, over and over again.
Find a pool, not one in an apartment complex, a pro one, like 25 meters or so.
Once the seconds hand on the clock hits 12oclock sprint across the pool, just one way. You should get across in about 20-25 seconds, or basically when the seconds hand hits 5 or so. Rest until the seconds clock hits 12oclock again, basically 35 seconds of rest, then swim sprint back across the other way.
So basically every time the seconds hand on the clock hits 12oclock you sprint across the pool. And rest until it hits 12 again. Do this 20 times, hence 20 minutes. The first 8 sprints should be relatively easy. You should be dying around the 13th or 14th sprint.
Swim sprints force you to keep your breathing on point no matter how exhausted you become, this is HUGE. You can't get that benefit with running your sprints.
Do it exactly like this once a week and you will become an exploding machine. Gassing will never become a problem. Takes about a month of this to fully take effect.
Another great thing about this is that you can do them by yourself. You dont need anyone to push you, you push yourself for the rest time. No trainer needed.