Negative splits...what a question! I've been trying to figure that one out for over twenty years without an answer but I do have some thoughts about why the elites can do it and we can't. First we don't practice it enough. Everyone is afraid to run fast in training, then run faster in training. We do a lot of GP running, but at maybe too short of distances and with too many rest intervals. It may be best to alternate doing a 3 miler at goal pace followed immediately by a 3 miler at faster than goal pace. Then recover to your resting pulse rate and repeat again. This may be a better way of doing a 12 mile run than a continouse 12 miler where we start slow and try to pick it up throughout with just the last 1/3 at MGP.
We also don't race at distances long enough to practice negative splits for a marathon. Today we race too many 5K's and don't have the oportunity to RACE (I MEAN RACE !!!) a 10 miler, 20K, 1/2 or even a 30K. Without these races, it's impossible to figure out a goal pace should be let alone determine negative split paces. The charts out there for interpolating what you can run a marathon in rarely work unless you have 10 milers through 30k races to plug in. For instance, using my 5K to 10K PR's showed I could have run 2:32:00. I ran 2:23:00. But by plugging in my best 10 miler or my best 1/2 marathon time theprediction table more accurately showed I could run a 2:21:00. This is much closer to reality but i never did that either. In other words we either need to race more at longer distances, or do more test runs to determine our ideal paces for the marathon. One problem runers make is to set up a 10 to 16 week training cycle yet not adjust our goal paces (either up or down) for where we are in the cycle. Test runs of 15 to 16 miles could do this as long as you duplicate the lead up days and you do your test on the same loop each time with weather being the only variable.
Looking at elite performances and compairing how fast these runners can race a 1/2 vs what they can run for their marathons we see they are much closer than non-elites. When they do the first half at 2 to 3 mins slower than their PR's they are to a lesser degree resting at closer to thier training pace. Then they race the second half at close to their 1/2 marathon race pace! We most often do it the oposite way because we don't know how fast we can actualy race the 1st half in before we are forced to drop back to training pace. If you look at splits in marathons for most of us, the first thing that happens before we crash is that we slow down to the training pace of our long runs. Then we crash. If we knew the correct pace using a series of test runs or longer races (not past Marathon pace) we could possibly use this as an opening pace then speed up the 2nd half. This would be a closer mimic to what the elites do.
I did test runs without knowing it because I ran all my long runs on the same course, Boredom, adding the 4 mile Grand View loop to get to 20 miles. So I guess I knew where I was in my cycle. I was always able to race 30'sec faster per mile in the marathon than my 20 milers on Boredom and my 2:23 pace was my normal pace. It was usually around 5:20 for my 12 milers on Boredom and around 5:50 for my 20 milers. I can't say this works for everyone but it's been the same for a lot of runners I worked with. I'm not saying to use Boredom for your long runs exclusively, but I do believe in running somewhere that gives you regular test runs.
I'm going to quit now because I need to do my workout. I think better on the move so maybe I will come up with more thoughts. You know me I like to talk about training the OLD WAY!!
When I swam competitively, distance was my specialty. We constantly worked on even pacing or negative splitting our races. The coaches felt by doing this one would conserve carbohydrates for later in the race, delay lactic acid build-up or reaching (or crossing) your anaerobic threshold too early in the race, and that you would be more efficient overall. You had to learn not to start out too hard/fast and settle in a pace you could maintain for the race, maintaining dead even splits or coming back a little faster than you went out.
Running is the same way. Look at the world records in the distance events. They were all done with even or negative splits. The front half is never more than 2-3% off the back half (e.g., out in 1:32, and back in 1:28 or vice versa for a 3 hour race). The hardest thing is to hold back in the early part of a race. You need to be cautious about not starting out too fast (Danimal) and cause the body to produce more lactic acid than it can handle. Once that reaches a critical point...the runner/swimmer will slow down or stop....it's the only way to clear it...
Greg and I worked and worked with Peggy Joseph on this type of pacing...wanting her to try and run even splits in the 15K at Steamboat. She was one who always went out way too fast regardless of distance, and tried to keep from slowing down toward the end and being passed. She hadn't won the 15K to this point in time. We worked with her a full year to where she could run even splits....not going out too fast...running somewhat conservatively early on....letting people go....only to keep her pace even and reeling in these runners as they slowed later in the race. She won Steamboat that year by running the second half of the 15k slightly faster than the first.
You need to establish a goal and your training should be geared toward reaching that goal. Run against the clock, not other runners. This will require you to hold back and follow your plan. Train at the pace you want to race at....tempo runs are great for this, or repeat miles done with very short recovery periods. Using a Garmin will help monitor pace for the miles and make sure you're on track.
I read one article on negative splits where it does state that it's very difficult to run even splits in a marathon, so it's usually better to err slightly to the conservative side than to be a little overly aggressive. Not by much...like an average of 5-10sec/mile over the first half...which is 1-2% for most runners. Another states that if you've accurately pegged your race goal, then it doesn't matter if your splits are positive or negative as long as they are no more than 2-3% apart...that close is essentially even splits. Terrain, weather, etc....all play a part in your plan as well.....
Running and swimming even/negative splits takes time, practice, and patience to the point where it becomes second nature. I practiced this in both my swimming and running (even in my 5K's) and felt that it made me faster overall in both disciplines. It was always nice speeding up in the second half when others were slowing down...it would give me such a mental boost passing people....
Hope this helps, Blair
Hope this helps, Blair