Let me first say that I have the utmost respect for athletes in MOST sports. I'm not here to single out any one sport but I am here to give an alternate view and opinion on training and sometimes stir the pot. Now, I'm very aware of the SAID principle (specific adaptation to imposed demands) and sport specific training. If you want to look like a bodybuilder then you train like a bodybuilder - I leave the training advice to the experts in their specific sport. Also, different body types, disabilities and injuries can determine the types of training you do (believe me I've had to work around my share of injuries). That being said, I am a firm believer in doing as many different training modalities as possible with the goal of being a "complete" athlete.
I'm going to go out on a limb and say that high end MMA fighters are the best athletes in the world - simply because of the variety of training they regularly do. (Emphasis on high end fighters. We all know every sport has a mixed bag of competitors). I say this without being able to run a marathon, bench press four plates a side or surf more than 10 seconds. I will however try to hit all of the training modalities below every week:
Plyometrics
Coordination drills
Sprint/interval training
Wrestling
Boxing/kickboxing
Olympic lifting
Long distance running (5 km or 10 km)
Weight training
Jiu-Jitsu
Sparring (close to full contact fighting)
Hiking/climbing
Movement drills
I call this "Full Spectrum" training. I am far from being a complete athlete but I get closer every day.
I always look at the "real life" worst case scenarios. What if I'm in a plane crash in the mountains and have to hike out and survive, or fight a bear (kidding)? I know many "athletes" that can't walk up one flight of stairs without being gassed. Aesthetically great, functionally, not so much. In the past I have been this person - more concerned with one aspect of fitness. I paid for it in blood and learned my lesson. I know now that when shit hits the fan that I'll be better off than most.
Analyse your training. What are you training for? If it's not for a specific competition then why limit yourself? How functional are you outside of say, a great golf swing or 100 m sprint?
Remember it's "Progress not Perfection".