Fitness Type - Can a sprinter become an endurance athelete?

Building endurance takes time. Be patient, build slowly, it will happen.

PS -- two miles isn't a sprint. A sprint is usually considered 400M (1/4 mile) or less. If you can comfortably run 2 miles, you're a distance runner already

I've seen all kinds of shapes, sizes, fitness levels doing distance running and triathlons. I have been told by my coaches that I'm built for speed. I've always been able to run fast 5k's, but never thought that I could do anything beyond a 10k. A few years ago figured since I play 90 minutes of soccer, I should be able to run a 1/2 marathon, so I trained for one and did. That encouraged me to go on to do a few more and eventually a full marathon, and last year I caught the triathlon bug. I have to admit, I'm slower going long distance. Not sure if it's my build, mental strength or what, but at the moment I'm training to improve my PB and am actually trying to lean out my normally thick lower body to see if it'll help. No leaning out much at all in that area so far though. Actually getting thicker... ai. Might need to lay off the protein.

I am also a sprinter, I ahve been trying to do a 5K, which I ahve accomplished, but I can't do the whole thing yet, not sure why.

I play Soccer, I can easily play three hours of soccer which is constant running, either a sprint/jog, more HIIT type of workout, and i love it.

But distance running is difficult for me, doing my second 5K this saturday.

I will probably never be a top endurance athlete due to various factors that I have no control over (body type, genetics, etc).
It is good to know that, by some of your examples, it is possible to achieve greater endurance and if I choose to I could work up to longer distances in running.

Totally! Just for perspective, I think genetically I am not meant to be a runner at all. I was TERRIBLE at it in school. I have vivid memories of being mocked for being the last kid to finish the mile when we'd have to run it in gym class. When I started running a little on the treadmill to lose a few pounds in college, I remember struggling to do 2 miles in 30 minutes with lots of walk breaks.

15 years later, after running consistently for most of that time except for a 5-year interruption for pregnancies / babies, I am still not fast enough to win local races or anything, but, my mile pace has gone from 15 minutes per mile for 2 miles to 7.5 minutes per mile for 2 miles; twice as fast, which is definitely progress. And my endurance has gone from a 2 miles at a time to 30+ miles at a time (with walk breaks) or 10+ miles at a time (no walk breaks). Other more gifted runners would probably be able to win lots of local races with the amount of time that I spend training, so yes, my performance is limited, but relative to where I started I have made huge progress.

As someone else stated, we all have genetically and environmentally programmed strengths and weaknesses. I'm naturally fairly strong for explosive tasks like weightlifting, but because of a minor birth defect ad childhood illnesses my heart and lungs are naturally a bit weaker than average. By your theory I should be a "sprinter". I happen to prefer distance running, and these days I can do 10K relatively easily (training for a half). Carl Lewis was a great natural sprinter, but I'm quite sure that had he put his mind to it he would have been a far better than average distance runner, though probably not world class.

Your natural inclinations can only take you so far, and for all but the highest levels of competitor, training is far more important than natural ability. It sounds to me like you're not training right. The trick to endurance running is, when adding mileage, go slowly. Both in the sense of running more slowly than you normally would, and in the sense of gradually adding miles. Add no more than 10% to your weekly distance, and no more than 10% to any single run. When you're running a newer longer distance, run slower than you normally would. If your average pace is 5.8-6.2 mph pick one day a week to be your "long run" and run 4 miles instead of your usual 3, but only run 5.5 mph, or 5.2. The next week make it a 5 mile long run. The week after that keep your long run the same distance, but try to do 4 miles on one of your shorter runs at closer to your normal pace. After a couple of months your long run is 6 or 7 miles at a slower pace, and "normal" runs are 4 or 5 miles at your current pace.

Of course, just like compound interest allows money to grow faster the longer it sits in an account, you can add mileage faster the more miles you're accustom to. If you usually run around 10 miles a week, the 10% rule means that you shouldn't add more than a mile.... Once you're up to 20 miles a week, you can add 2 miles, etc.

How often are you running those two mile runs? I ask because if your total volume is very low then progress is also going to be very slow. Ideally, if you want to be an endurance runner you should work toward upping your mileage over time to at least 40 miles per week. At that point you get a large part of the benefits of volume without increasing the chance of injury too much.

**(You will still improve at lower volumes but you will not improve as much or as fast and you will never know the answer of how good you could have been)

Getting up to new and further distances the first time is always hard because it is above what your body is conditioned to do. After it adapts the distances become much easier. For reference, when adding new distances or intensity to running workouts it takes the body 3 to 6 weeks to adapt to the new workload.

Someone once told me that people are GENERALLY categorized as sprinters type athletes or endurance type athletes. I think this has to do with many variables including muscle types, body types, genetics, fitness history, and probably 100 other things.

If this is true, and it feels like it might be based on my experience, can a person truly change their fitness type?

I ask because my experience has shown me that I feel strong early in a workout but after about 20 mins or so I tend to taper off very fast.
For example, I've been jogging for about 6 months or so fairly regularly. I usually jog around 5.8 - 6.2 miles per hour. When I go jogging I am good for only about 2 miles. I usually try to squeeze in a 3rd mile but it is a rough 3rd mile.
It should be said that I truly enjoy those first 2 miles. I really wish that I could enjoy longer distances like some of you runners out there who somehow are able to knock out 10Ks like it's a normal everyday thing. I just cant seem to get past that 3 mile mark
Should I resolve myself to the fact that I am more of a sprinter type and stick with my 3 mile distance? or
Am I just impatient and to truly change my fitness type requires more time?

What are your opinions and experience?

Genetics are overrated when it comes to the fitness level of average person. Yes, at the elite level, genetics will come into play, giving some an edge over others despite very similar training loads. But this is not going to be a factor when deciding whether you can run 3 miles at a time.

3 miles is not that much of an endurance. I think nearly anyone, with proper training schedule and diet (assuming no injuries/ other health limitations) can certainly run at least 3 miles at a time. It sounds like your problem is that you are trying to run too far too fast. Why not try adding a tenth - a quarter of a mile each week until you get up to 3? There are also C25K sort of programs where you alternate walking and running. Once you get to 3 miles, you can decide whether you want to push your endurance further. There is the bridge to 10K from there, or you can google running programs to see what you find. The important thing for increasing endurance is to have patience. :-)

Considering the prospect...

*cold-chill shudder*

Genetics do play a part, but yes.

Endurance takes time and patience.
I am/was a fast sprinter. I am now a marathoner and a fairly serious endurance runner.

Train smart, build slow and it will come.