Miami Heat forward LeBron James plays against the Memphis Grizzlies in the second half of a NBA basketball game Wednesday, April 9, 2014, in Memphis, Tenn. The Grizzlies won 107-102. (AP Photo/Mark Humphrey)

It's one of the least answerable questions in sports. But here's one expert's take for Fitness Friday.

I asked Jeff Potteiger, dean of Graduate Studies and a faculty member in the Movement Science department at Grand Valley State University in Allendale, Mich., how he would approach this debate. Potteiger is also a fellow of the American College of Sports Medicine.

Which athletes do you believe are, overall, the fittest?

First, we have to define what "fittest" means. There are a number of ways that you can measure fitness...Let's take body composition as one measure of fitness. For many athletes, having a low level of body [fat] is particularly important. So if you take a look at sprinters in track and field, or distance runners in track and field, they have a very, very low percentage of body fat, and they do very well. If you take a look at maybe, long distance swimmers, or professional football players, in particular offensive and defensive lineman, they have much higher levels of body fat, and one can certainly argue that they still do well in their sport.

So when you're talking about fitness, you have to identify the parameters, and you also have to identify what particular sport you're talking about.

If we're going to compare disparate sports, what criteria should we use?

I think you have to use cardiovascular fitness. I think you have to use anaerobic power. I think you have to use muscular strength. You have to use muscular endurance. And I think body composition as well, comes into play when you're talking about overall fitness....

One could certainly argue that if you throw a ball 95 miles an hour, or you have a great knuckleball or a great curveball, you can do very well, but you don't necessarily fall in [the category of] the most fit athletes in the world.

Could you give us a definition of anaerobic power? That's the one that's not sort of self-explanatory.

That's the power that you generate in the human body in a short period of time. So, for example, if we're talking about a 100-meter sprint or a 40-yard dash for football players...It's defined as the force that's generated times the distance that the object moves, divided by time. So if you're talking about speed times mass, a football player running a 40-yard dash in 4.3 seconds, then that person tends to be very, very powerful.

...It's a little bit different than quickness, because it does take into account how much force is being generated.

Okay, so does that bring us back to trying to make this comparison?

...I've got to think there are certain groups of athletes that would be right up there at the top. So I'll just list them for you: ...I would think that basketball players are probably pretty good overall athletes, and have a pretty high level of fitness in all those areas. I also think that defensive backs in football probably have some of those attributes as well. ...I would probably start with those two.

When you get into other sports, there's generally something missing. So, for example, let's take wrestling. They've got great muscular endurance, they've got great flexibility, they have great power. They probably have pretty good cardiovascular fitness. So I would put them, maybe in the top, oh I don't know, five or 10.

I think another position in football would probably be the linebackers. Generally pretty quick, generally pretty fast,  pretty good size. Generate a lot of power. They would probably be right there.

Let me hit you with a couple that I've read about. Boxers?

Yes, absolutely. I think their muscular endurance is very good. I think their cardiovascular fitness is very good. I have to be honest with you, I'm not so sure about their flexibility...Obviously they have great hand speed, so they have quickness in their upper body.

...If you took boxers and you tried to put them in another sport, I don't know how well they would do. They're certainly very fit.

How about decathletes?

I think decathletes are right up there in the top five as well. The thing about the decathlete, though, is when you think about the events they have to do, some of those events are what I would call more endurance type events. When you get into an endurance type of event, you can't really carry a lot of muscle mass. Because obviously if you've got to run 400 meters, or you've got to run 1,500 meters...you've got to carry that mass as well. So they tend to not be as powerful.

...If you think about what football players have to do, or basketball players, with quickness and agility and speed...if you're up and down the court for 40 minutes a game in college or 48 minutes in the NBA, you've got a pretty good level of fitness as well.

One more: soccer players.

The thing I think I would be a little concerned about soccer players is, again, the power. They tend to be more on the leaner side. Certainly they have great cardiovascular fitness. Pretty good quickness. Flexibility is probably pretty decent. Outside the legs, I would be concerned a little bit about how they might match up in a power measurement.

And I forgot hockey players.

...They're in pretty good physical condition...They're really pretty flexible. They're pretty powerful. Their body composition is pretty good as well. And they have decent cardiovascular fitness. So...I'd probably put them in the top 10.

...I think it would be really cool if you get a group of people together who would say: here are the six, seven, eight physical characteristics that define fitness and what do we know about the athletes that are out there who do well, and that have high VO2 max values, or high muscular power values?

You'd probably end up with someone who looks like Bo Jackson or Jim Thorpe, or maybe Deion Sanders.

Bo Jackson doesn't necessarily get the credit he deserves as one of the all-time great athletes. The guy played two sports at a very high level, and don't forget he played one sport with an artificial hip. It wasn't just that he could hit. He still had to run. One could certainly argue that if you had to pick individuals, that he would be right there at the top.

I think LeBron James...I think he could be successful in a lot of other kinds of sport. The one thing that might hold him back in some sports is being 6-foot-8, 6-foot-9, something like that. When you're that tall, it's tough for some sports. People say 'oh, he would be a great tight end [in football].' He'd also be a big target. He's a little bit easier to hit.

...I think Deion Sanders was one of the top all-around athletes.