KCgeezer wrote:
Date: M1 split - M2 -- M3 --- Finish
5/6: 5:52 - 5:56 -- 6:05 --- 18:13.9 (64F at start)
5/28: 5:42 - 6:02 -- 6:32 --- 18:58 (84F index at start)
6/24: 6:02 - 6:06 -- 6:22 --- 18:43 (64F at start, XC course)
my suspicion, though i have no data to support it (just hunches and extremely limited experience, at least with longer distances), is that negative splits are not necessary, and maybe even counterproductive, in races 800m or shorter. i think the mile/5k probably benefit the most from straight out even splits, and 10k and above may require negative splits.
temperatures mentioned above should not affect each race, except for relative to each other. yes, on a warmer day, you may consider starting slower, but it should not affect whether or not you're trying to do negative splits or positive splits, at least not in a 5k in my opinion. that said, if you are affected by the heat more than average, then absolutely exercise caution in the early going and shoot for maybe more extreme negative splits.
at the risk of pointing out the obvious, if you know you're in 18:13 shape on a flat course, why you'd ever go out faster than 6:05 baffles me. if you're hoping for pulling a surprise outta nowhere/running over your head, i'd still go 12:10 through two miles, and if that miracle effort is going to happen, let it happen over the last mile. if you run 5:30-5:50 the last mile off that pace, then, AND ONLY THEN, should you maybe reevaluate starting pace. if you crank out a 5:55, then i'd call that a well-executed race.
for the record, there are absolutely times when you should go out too fast--sometimes you have to adjust to competition environment, etc. but if you're trying to execute your best paced race, AND you feel confident about assessing your fitness, wear a garmin and be disciplined the first two miles.
also, i'd agree with other posters: negative splits can definitely be practiced. progressive runs are fairly vogue these days--on my long and short tempos, i always try to make sure my last mile is my fastest. back in my younger days i used to do something my coach called breakdown miles (usually 2 of them, full recovery) on the track--and yes, this workout was feared by all!--where you'd pick it up two seconds every lap (choose your starting pace wisely!). at our best fitness, the last lap should mirror close to mile race pace (for example the fastest one i did was 64/62/60/58). if we didn't hit the proper pace through the first 200, he'd stop us, let us recover, then we'd try again. at least for the mile, this taught me that in a real race, you had to pick up the effort every lap just to maintain pace.
hope this helps,
cush