I haven't run very much since reinjurying my groin in October, maybe 5 or 6 times in the last few weeks. The runs have been easy pace since sprint intervals caused the initial injury in January and the recurrence in October (for the barefoot curious, I was barefoot for the first injury and shod for the second time). My groin injury has improved, in part I believe to both restricting running and adding core exercises, but I still feel a twinge where I shouldn't every now and again.
Perhaps against my better judgement, I ran a 5K on Thanksgiving Day to "test it out". If anything, I felt I needed to justify those extra calories that I consumed on Thursday, and boy did I. And I've been anxious to get in a race mode because recent weight loss should produce faster times. But I also knew I shouldn't try to run a fast time for me, perhaps in the low 20s minutes would be alright.
I did make a different kind of time related goal, though, to run a negative split. For those not familiar with running jargon, a negative split is a description of running the second half of a race faster than the first half. I don't think I've ever run a negative split. It's not easy in the beginning of a race to hold back some juice for later. I recorded my pace data with my Garmin 305 (data charted in Excel).
My race time was just under 22 minutes, just about what I thought I would do. My pace was what I was pleased with (blue line on chart). The first half felt comfortable. Every so often, I would catch myself trying to catch runners ahead of me and have to back off the accelerator. It's curious that there were 4 pace spikes (noted with green markers on chart) in the first half at about equal distance intervals. It's as if I couldn't decide which pace to run, although there were a few small hills in the first half that slowed me down.
The 70 foot elevation climb at mile 2 (3200 meters) was a bit surprising and definitely affected my pace, both on the decline and incline. After that hill I had the juice to push it harder and get the negative split. The straight blue line on the chart shows the acceleration. My pace in the first half (2.5 Km) was 7:13/mile and in the second half was 6:56/mile. Nothing really bad happened in the race despite pushing it a little, so I think I passed "the groin test". But this race was my only run of the week and my groin was sore for about a day afterwards.
So what was the point of the negative split? Would the result be just as good if I ran a more even pace throughout the race? It's a difficult question to answer, really, but I can attest to the psychological boost from passing runners who are clearly hurting more than I am. Just maybe, the negative split is a synergistic effect and produces an improved performance otherwise.