- The second half is faster than the first half
- The second half is the same as the first half
- The second half is slower than the first half
If the second half of a run is faster than the first half, the strategy is called a negative split. In order to do negative splits, runners must conserve enough energy to allow them to run faster during the second half. The conserved energy is used to not only overcome the effects of becoming tired but to do that and also run faster. This is desirable, because it means the runners avoid going out too fast at the beginning. Negative splits are desirable on courses where there are more/steeper hills during the last half than during the first half. Most runners consider this the best strategy.
The easiest way to measure splits is to carry a GPS that measures split times. If you don't have a GPS, you can always use a stop watch and record the split times on your hand.
If the last half is run at the same pace as the first half, the strategy is called a flat split. In order to do flat splits, runners must conserve enough energy to allow them to hold a steady pace, the conserved energy being used to overcome the natural tendency to slow down as one tires during the run. Most runners consider this a good strategy because it means the runners avoid going out too fast.
If the last half is run at a slower pace than the first half, the strategy is called a positive split. Positive splits mean the runners didn't have enough energy left to keep a constant pace, much less a faster pace, during the last half of the run. Three common causes for positive splits are (a) going out too fast at the beginning, (b) running a longer distance than is appropriate for ones body-condition, and (c) encountering more or steeper hills during the last half than during the first half. Most runners consider positive splits a poor strategy.
When runners are significantly increasing the distance of training runs, it is common to run positive splits. The runners are not used to running the longer distances, and they becomes tired during the latter part of the run. This means it may not be appropriate to worry about splits until runners levels off in distance and their bodies have adjusted to the new mileage. In addition, it is also common to run positive splits when the course has more hills or larger hills than the ones the runner has been running. But, when the time comes that runners can handle the distance and the hills, then they should decide on the strategy to be used.
It is not easy to learn to run flat or negative splits. Runners must learn to start out slower than "normal", and they must learn to maintain paces that will conserve energy during the first half of the run. When changing from one running route to another route, runners must adjust the pace used during the run. Learning to run flat or negative splits is a rewarding experience, though, because it means the runners have mastered both their bodies and the course.
If runners are running for enjoyment and are not training for racing, they may have little need to worry about splits. They can just run at their comfortable pace and enjoy the experience. However, if they are training seriously for racing, they will need to master the techniques of negative and flat splits and thus maximize their performance during the race.