Sunday December 3, 2006, four miles indoors

NSP Community Center track again, 4 mi in 35:54, pace 8:59, splits 8:58, 8:55, 9:00, & 9:00. A little experiment today. Since the idea was to run four easy miles anyway, why not put on the heart monitor and measure the heart rate at exactly nine-minute miles, because it's so easy to do an exact pace at the track. The average rate was 127, and the steady-state rate after leveling off was 132. It's my recollection that nine-minute miles used to get my heart up to a higher rate, close to 140. Looking back in this log, I see a heart rate of 143 for a six-miler in May 2003, and 141 for a 19-miler in April 2004, both at nine-minute pace. Of course it makes sense that the rate is down, because my race times have gone down too.

So what physiological changes account for the decrease? An increase in running efficiency would result in less oxygen uptake. Also, the cardiopulmonary system itself may have become more efficient, so that one beat of the heart can pump more oxygen. I think probably both. I wonder how much farther I can take that before age starts to reverse the trend.

I've previously thought that my maximum heart rate was about 167. If so, then today's nice easy sub-marathon pace was at 79% of max heart rate. Is that normal for an easy pace? Seems like I've read that 65%-70% is a target for long-slow distance running. Need to do some research.