“Of course you’re slowing down — you’re getting older,” the voice whispered, and I hated it.  But it was true:  this morning’s 1-mile repeats were disappointing, averaging around twenty seconds slower than earlier this year.  “Age is catching up with you,” the voice continued, its tone at once insinuating and damning, “it’s getting harder to sustain speed.”

It’s not the fist time this voice has piped in; actually, I’ve heard it on and off for years.  But when I looked at the data, I interpreted a different story.

The data consists of speed and average heart rate for 1-mile repeats dating back to 2006, and you can see it plotted on the chart below, where each dot represents a single 1-mile split, with the vertical axis indicating the time, and the horizontal axis indicating the average heart rate in beats per minute.

The heart rate data is meant to proxy for “effort,” with the idea being that a slow mile at low effort is just as good as a fast mile at high effort.  To understand this relationship, take a look at the blue diamonds, which represent mile repeats from 2006-2007, and the solid blue line, which illustrates the best statistical fit for these data points.  Back then, an average heart rate of 130 beats per minute would have corresponded to an 8:45 pace, while at 165 beats per minute, the pace would have been 6:45.

This morning’s repeats were disappointing relative to faster times earlier this year, but the long-term trend has been very encouraging.  The brown line shows repeats from 2008-9, and it’s consistently lower than the blue line, or put differently, after two years of training, I was running close to 30 seconds faster at every level of effort.  The green line shows data for 2010-12, the orange line for 2013-14, and the red line shows the repeats I’ve run so far in 2015.  Each line is lower than the previous year.  Today, at a heart rate in the mid-160s, I’m running 1.0-1.5 minutes faster than when I started logging data nine years ago.

Why were this morning’s repeats slower?  I seem to have run a little conservatively, with average heart rate in the 150s instead of the 160s, and I think that’s because my body’s not feeling totally comfortable at high speed.  I took a hiatus from speedwork during the early fall while a couple of injuries healed, and my mileage fell dramatically.  In fact, instead of running, I spent much time hiking barefoot in the Catskills at a very, very slow pace.  In the coming weeks, I’ll work in some high-intensity shorter distance repeats (200-meter and 400-meter splits).  These should help the mile times.

I really hate that smarmy little voice, the one that whispers so condescendingly, warning me that age is going to slow me down.  Why?  It wants me to quit.  But I have no intention of doing so — even though I know it will one day be right.

All things are numbers

— Pythagoras of Samos (c. 582 BC – c. 496 BC)