I'm in a situation where running and biking each morning 5-6 days a week has become lucrative. Some of it is to get out of the house, the other is to lose some weight. I've never been a strong runner and very slow. I was a very fast sprinter comparatively and have always done explosive activities and done them well. I learned that fast and slow twitch muscle fibers existed so I attached to this concept as to why I was good at these activities. Because of this knowledge I limited myself on cardiovascular excellency even though I could bike 20 miles when in shape several days a week. I learned this week after starting training several weeks ago that people can also become versed at long range exercise if they have good metabolic adaptations which are also genetic. So we'll see if I can get faster. My goal is to get into shape where I can do tempo runs for 20-40 minutes (a tempo run is where you run at a pace that will be hard, but not too hard that you will stop within an hour of running, its just enough to allow enough oxygen to get to your muscles. Think of a 1000 meter run pace). I am going to swim in the pool and am working this into my schedule. I was able to swim 9 laps with 30 seconds to 1 minute of rest each length.
I'm currently running a 10 minute mile
5 miles on the bike in 28 minutes with some hills
Core exercises during the end of the workout
9 laps in the pool with rest each length.