I was out there this morning doing the second in my summer series of benchmark runs, just about half way through the crucial measurement lap, when what should happen but I gradually gain on and draw level with Horst, father of Namban junior, Friedrich. I haven't seen him for ages, and his country has just come third in the soccer World Cup, so it would be a bit rude for me to just run ever so slightly away from him. The result is that I do slow a little, and he does speed up a little so we remain together for the rest of the lap, discussing all the what-might-have-beens of the WC. My average heart rate for the lap is 147, or 79% of max compared to last week's 149 (80%). And as a result, the time this week is slower: 4:28/km last week versus 4:37/km this week. So should I chuck that data point down the gurgler?
Well, it got me to thinking about how I could convert these data into some sort of a heart-rate adjusted fitness index. I'm not sure yet if it is valid, so I'll describe what I came up with and see what people think. What I decided to do is divide the number of seconds faster than 5:00 pace by the number of heart beats above 130. So, how many seconds of pace better than 5:00/km do I get per heartbeat above 130 at the given heart rate. Compre? It means if I run at 4:30/km at a heart rate of 160, the index would be 30/30=1sec/hb. But if I became fitter and the pace at 160 heart rate became 4:00/km, then it would be 60/30 = 2 s/hb -- I am now getting two seconds of pace per heart beat over 130. In other words, bigger number means fitter boy. In theory this should help the comparison of numbers like this week and last week, where something went slightly wrong with the pacing.
Well, the index for last week was 1.684 and this week 1.353. So, on both measures, straight pace and heart-rate adjusted fitness index, I did worse this week than last week. Possible reasons include heat/humidity (not much difference), lack of toilet break this week (greater cumulative heat load), total mileage of the week before last (two weeks back I only ran 48 km), or fatigue from last week (circa 85 km). If the last two factors hold true, then next week should show an improvement as response to last week's mileage kicks in. We'll see. I'll show a graph next week.