I'm sipping a cold brew coffee and listening to Santana without a shirt on. It's hot enough to have all the blinds down, hot enough we dream of air conditioning but not so hot we actually succumb to the temptation. It was mostly this hot at 7:55 this morning when I parked the truck outside the high school pool entrance, watched my daughter go in for practice, and set off down the road at a trot. Coming off two days without running, my legs didn't feel like my own. I told them what to do, but didn't feel connected to them. 

I need to be connected to them. Sure, all of us need that, but I'm planning a 50-mile run the day before my 50th birthday. That gives me a big push to know my body in ways I haven't before. I'm not trying to get back to when I was as a younger man or boy. Then I didn't pay much of any attention to my body. I expected it to do things, and it usually did them. I didn't expect a four-minute mile, but of course I could play basketball for hours, hike a mountain trail, and simply keep going. I still expect those things, but as I approach 50, I'm also approaching limits. 

I don't think of limits as fences, barriers, or walls. I imagine the limits I learned in Calculus where a limit is the value that a function (or sequence) 'approaches' as the input (or index) 'approaches' some value. 

Instead of a wall to hit, I keep approaching limits at a slower and slower rate. Imagine the graph y=1/x (which, if we were still in Calc class, would be written f(x)=1/x). Try it. Find a piece of your kid's graph paper and start at x=1. You'll put a point at (1,1) because 1/1 = 1. Move to x=2 and put your point at (2,1/2). Keep going out to about x=5 which gives you (5,1/5) and you'll see that you have a curve sloping down toward the axis. If you had an infinitely sharp pencil and infinitely sharp eyes (something I lack at almost 50), you could go on infinitely and still never hit the x-axis. For all intents and purposes, your line hits the x-axis even though logically it never can. The limit as x approaches infinity approaches zero, but never quite gets there. (My crude sketch of this function is at the top of this post.)

Just for fun, move the other way on the graph. Go to x=1/2 and plot a point at (1/2, 2). Follow that with (1/3,3), (1/4,4), and (1/5,5). As you move closer to the y-axis, the graph goes up. The limit, as x approaches zero, approaches infinity. Cool. 

Unlike limits, I'll approach and hit 50 then go through it for many years, God willing. No limit there. Simple linear arithmetic. 

Okay, back to running and approaching 50. Remember, as a kid I expected my body to just do whatever I wanted. As a catcher in little league, I expected that I could and would throw down to second base with enough velocity and accuracy to pick off any kid who hadn't gotten a good jump against my pitcher. At one practice when I was 11 or 12, our coach lined three kids at first base, a pitcher threw, and the first kid tried to steal second. I threw down and picked him off. The pitcher threw again, the next kid took off, I threw down and almost got him. It went like that for an hour. I went home with my right arm feeling like it might fall off and was pretty sure it was three inches longer than my left, but knew that I would throw down to second the next day and do it better. My job was to pick off runners and I did it. No question. 

This morning, with my daughter at swim practice for two hours, I chose to do two five-mile loops of the course I'll run ten times August 25th. It was hot, my legs felt connected to someone else's body, and I remain twenty pounds too heavy. Still, I know ten miles is within my limits and fully expect that so too is fifty. No matter that I felt lousy for the first mile and a half. I knew I would loosen up and I did. After five miles, I was worn down but not worn out. I had something left and went for a second loop.

On a graph, I'm at x=49.9 years, on a line with arrow, what's called a ray, except those go on forever. I'm not theoretical, so eventually my line will end as my father's did three years ago, but for now mine goes on. I'm pushing forward. My limits all seem theoretical. 

The loop on which I run has two tough hills and two minor ones. It's a fairly easy five-mile run, but will be challenging for ten circuits. I could map a flat course, but I want hills. They are a chance to investigate the limits. 

There is a chance I'll come up hard against a limit. I thought about that today as I tried to cut into my time. I'm not a fast runner, but with two miles to go and the hills behind me, I was averaging 12:06 per mile. Could I get below 12? I picked up the pace. Three blocks later I was at 12:05. I kept pushing toward a 12-minute average pace.

I think about records such as Roger Bannister's first-ever four-minute mile, run in 3:59.4. Amazing. But of course that record has been broken and broken and broken since. The current mark is Hicham El Guerrouj's 3:43.13, a full 1.26 seconds faster than the previous record set six years prior. Records will always be broken, yet the mile cannot be run in zero seconds. There are limits, but no one knows what they are. The science used to say a woman's uterus would fall out during a marathon. And before Bannister, many believed a four-minute mile was impossible. 

No human will ever run a two- or even a three-minute mile. But 3:30? Sure. It probably won't be in my lifetime, but then again there's Bob Beamon who beat the long-jump record by nearly two feet. Tell him about limits. We just don't know. 

I'll never run a four-minute mile. I have no expectation my body is meant for such things. When I mention that I'll soon run 50 miles, people shake their heads. "You're crazy." Maybe, but it doesn't feel like that. I've simply decided my body can do it. I have some history with distance: the half-marathon, a 50K. I understand pacing and perseverance. It may be that I can't run 50 miles this August, but I doubt I'll see it as a limit. I'll just need better preparation, milder conditions, or a flat course. My body can do this. I'm pretty sure. 

Pretty sure is as far I get until I do it. I did ten miles today despite weird legs and high temperatures. I'm preparing, testing my limits. Two miles from the end, my watch read 12:06 per mile. I pushed through 12:05, 12:04, 12:03, 12:02, 12:01. In the last mile I knew I would beat 12:00. I smiled. My shorts were so wet with sweat, it was as if I'd jumped in the pool. My heart beat at the upper limit of my training zone. My right arm hurt due to an old neck injury (perhaps all those throws down to second base), but I kept going. 12:01, 12:00, and 11:59. I smiled again but kept going.

Back at the pool within my two-hour window (I hate to keep my daughter waiting), my watch read 11:55 per mile for 10.2 miles. Too tired to celebrate, I nodded and blew air from my lungs. What's to celebrate? My body did what I supposed it could do. I pushed the limit a little closer, but there remains daylight between the line of my life and the axis of termination. I tell you, these limits, it's almost as if they go on forever.