The most impressive Game 1 stat from LeBron James wasn’t his 32 points, 13 rebounds, 3 assists or 3 blocks, and it wasn’t his customarily efficient 13-for-22 shooting line. Somehow, even though Miami’s starters were pulled with two minutes left in the fourth quarter, LeBron still played 44 minutes.

He’s listed at 6’8 250, but he weighed in at 245 pounds before the 2003 draft, and he’s obviously put on a significant amount of weight since. Muscle, after all, weighs more than fat, and there’s a whole lot of muscle on his frame.

A man his size should not be able to sprint up and down a 94 foot court while routinely blowing by NBA guards and overpowering NBA forwards at the front of the rim. LeBron keeps himself in phenomenal shape, which is one of the reasons why he is rarely in foul trouble, as fatigue never has him out of position to where he needs to commit a silly foul.

As a result, the Miami Heat never let up the pressure on an opponent’s back-line. With either Dwyane Wade or LeBron is on the floor for all 48 minutes, having a shot-blocker on both your first and second units is almost a necessity.

It’s a huge problem for an undersized Boston Celtics team that only plays one conventional big man (Kevin Garnett). Without Garnett in the game, the Eastern Conference Finals is a conga line at the front of the rim for Miami. Doc Rivers could only take him out for two-minute stretches in the second half, with Boston -3 in the third quarter and -2 in the fourth without him.

One of the most underrated features of the Dallas Mavericks team that defeated Miami last season was the sheer amount of size and length they had in their front-court. Not only did they have future Defensive Player of the Year Tyson Chandler, they also had a 7’0 260 defensive specialist (Brendan Haywood) and another athletic 6’11 230 center (Ian Mahinmi).

In contrast, when Garnett is out of the game, Boston has a 6’8 jump-shooter (Brandon Bass), and two skinny 7’0 (Greg Stiemsma and Ryan Hollins) who have bounced in and out of the NBA since leaving college.

The importance of depth, especially in the back end of your rotation, is one of the biggest differences between the regular season and the playoffs. LeBron averaged 37 minutes a game in three regular season games against the Celtics. The seven extra minutes he was on the floor in Game 1 were seven minutes Rivers could buy in the regular season with whatever backup big men he could scrape together.

It’s easier to expose an inferior player in the playoffs, as they are playing a larger percentage of their minutes against front-line players. In the regular season, Indiana’s 10-man rotation was a weapon; in the playoffs, just having Tyler Hansbrough and Lou Amundson on the floor was a huge liability.

For the Celtics to have any chance in the ECF, they’ll need Garnett to dominate defensively while orchestrating their offense as the one player the Heat don’t have a match-up for. In his prime, he might have been able to handle that. At 36, in his 17th season in the NBA, it’s unfair to even ask.

With the type of offensive and defensive responsibilities Garnett must bear, he’ll need his rest, even if LeBron doesn’t. But while having a superstar whom he can keep on the floor for entire halves is a huge luxury for Erik Spoelstra, it’s still something he should monitor closely as the playoffs continue and the minutes pile up.

LeBron averaged 43.9 minutes over 21 games in the 2011 playoffs. The only post-season where Michael Jordan averaged over 42.8 was 1986, when the Chicago Bulls were swept out of the first round by Larry Bird’s Celtics.

And while most of the discussion of the 2011 NBA Finals centered around whether LeBron shrunk from the moment, the sheer toll of all those minutes and the exhausting two-way effort he put into them must have had something to do with his subpar performance. Particularly when the Mavericks could roll out an endless stream of athletic 7’0 to bang and jump with him whenever he came into the lane.

With Chris Bosh out, Miami has needed LeBron to be inexhaustible. Whether that can continue for another 10-12 games will be one of the most fascinating storylines of the 2012 playoffs.