Thursday, 3 November 2011

The Art of the Negative Split with the Cut-in

On one of my favorite Podcasts Marathon Talk they are constantly talking about running Negative Splits.

For those that dont know what a negative split is. Its when you run the second half of a race faster than the first half.

There are a number of benifits to running a negative split in a longer endurance race
  • Reaching your lactate threshold later in the race, which makes you feel like you have more energy and allows you to run faster over the last few miles
  • There is a Physcological advantage to running faster than the competition in the closing stages of a race.
  • Conservation of Glycogen stores during the slower first half.
  • A faster post race recovery.
  • A more pleasurable race experience overall as your 'time on the limit' is reduce.
 Still not convinced? Stop and consider that many World records across various endurance events are achieved with a negative split, the famous 50.5 :  49.5  ratio being the most effective.

The traditional Negative Split has you complete the race in thirds, the first third a little under pace, in the middle accelerating upto pace, and then finishing the last third strong, and kicking with whatevers left.

Unfortunatly there is one major downside to all this, that strategy doesnt apply well to the Marathon where any increase in pace in the final third is usually beyond the abilities of most runners. Instead the best approach to a marathon is to try and run a constant pace throughout. There is of course one qualifier to assumes that you had plenty of time to warm up prior to the race.

Most Marathoners are not afforded that opportunity, as they stand in corals waiting for the start gun, or if its a small race and there is room to warm up we tend to stand around anyway and save our energy for the race.

The single biggest mistake that marathoners make is that they start too fast. The body is flooded with race day adrenaline, the gun goes off, the crowd surges foward and suddenly everyones running 20-30 seconds per kilometer faster than their target race pace... what makes this even worse is that your doing it on essentially cold legs.

When your running the marathon you want the energy required to run to be drawn from a combination of stored glycogen and fat burning. You'll never make it to the end just on glycogen alone. However It takes a while for your body to react to the stress of running and start up the mitochodrial furnaces that provide energy through burning fat... in the interim all energy needs are met from your glycogen stores. It is not uncommon for runners to burn off over 20% of their available glycogen stores in the first 5k.

It can take your body several miles to get warmed up. After that, your muscles are charged, your joints lubricated, and mood-boosting endorphins flood your system. You’ll find yourself running faster without feeling any more effort.” - Jeff Galloway, Runners World

The way to avoid this problem, and also deliver that oh so desirable negative split is to use the Cut-in. The Cut-in has you run the first few kilometers slower than race pace giving your body the time it needs to warm up. 

For a basic cut-in determin your target time and calculate the pace required to achieve it. Start the first Km 30 seconds slower than target pace, run the next 2k 20 seconds off pace, and the 2 after that 10 seconds off pace. At km5 you will be 1:30 behind your target pace. The rest of the race you consistently run 3 seconds per Km faster than the target race pace.

The Cut-in however does require several things. Firstly you need to be able to make an honest and realistic estimate of your Race day potential. If you set yourself a target time of 4:10 but are really only in 4:40 shape then the plan will fail and you will bonk. Using a race in the weeks leading up to the main goal is a good way to get an estimate, plug the time into an equivalent performance calculator like the one at McMillanRunning to get a good estimate.

You will also need the discipline to hold yourself to the paces during the cut-in phase. Certainly no easy feat when the adrenaline is surging, and the runners around you all seem to be going past they do say to yourself that you will be seeing them all again later in the race....some much earlier than you expect. It pays to practice the cut-in during some of your weekly runs.

Finally it would also pay to have done several steady state runs at the target pace - 3 seconds that you will want to run the majority of the marathon at... This should be the pace used in all Marathon Pace runs in your trainign schedule.

If you follow through on the Cut-in then you will also find that you automatically run a negative split. You will have conserved your energy for the later stages of the race where youll be passing people left and right that are struggling with the wall. Youll run to the finish line feeling great, and may well set yourself a new PR.

Start Slow to Finish Fast!


If the course is really hilly and your not going to be able to use pace then you can also use effort, a good measure of that is your Heart Rate. ... go through a cut-in on a flat course record your heart rate at the various paces and then use that as a guide to how to control the effort on a hilly course.

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