Negative Splits

by Jason Karp, PhD

I used to coach a talented runner who ran the first mile of every race too fast, only to slow down dramatically during the latter segments and end up disappointed with the result. He thought he was better than his workouts and he let his competitive spirit and pre-race adrenaline obscure his knowledge of his true fitness level. It was frustrating to watch him start off so well and get slower with each successive lap of the track.

The faster you run the first mile of a race, the more your muscles rely on anaerobic metabolism to regenerate energy (ATP) for muscle contraction. With the greater reliance on anaerobic metabolism and muscular work comes an increase in muscle and blood acidosis and the accumulation of a number of metabolic by-products that cause fatigue. Whether the race is a mile or a marathon, you can't put running time in the bank. You will end up losing more time in the end than what you gained by being "ahead of schedule" in the beginning. No matter how strong your will is, the metabolic condition caused by running too fast too early will force you to slow down during subsequent stages of the race.

Although race strategy sometimes dictates that you change the pace during the race to challenge your competitors, the best way to run your fastest possible race is by starting out at the pace you can maintain the entire race. While it may feel easy early on in the race to run the first mile at the same pace as the last, your patience will pay huge dividends during that last mile. Ideally, the second half of your race should be equal to or slightly faster than the first half (i.e., negative splits). To negative split a race requires accurate knowledge of your fitness level, confidence to stick to your plan when others have taken the early pace out too fast, and a good dose of self-restraint.

When you race, you don't run at some arbitrary intensity. The percentages of your VO2max and lactate threshold you can sustain for a specific amount of time are predictable. The longer the race, the lower the percent VO2max at which you'll run it. Research has shown that the speed at VO2max can be sustained for only about 7-10 minutes. Talented, highly-trained runners therefore race 3,000 meters (about 2 miles) at 100% VO2max, 5,000 meters at 90-95% VO2max, and a marathon at 80-85% VO2max (about 95% of lactate threshold). Your workouts, which should be performed at specific speeds that correspond to specific percentages of VO2max or lactate threshold, are invaluable for providing you with knowledge of your fitness level and for predicting your average race pace (assuming you account for such things like the terrain and the weather). As I tried to convince my overzealous athlete, your workouts don't lie.

For highly-trained runners, 5K pace is about 20-25 seconds per mile faster than lactate threshold (LT) runs, or about 10-15 seconds per mile slower than VO2max intervals. 10K pace is about 10-20 seconds per mile faster than LT runs, or about 25-30 seconds per mile slower than VO2max intervals.

Dr. Jason Karp is owner of RunCoachJason.com, a coaching, personal training, and fitness consulting company, offering science-based coaching to runners of all levels, fitness training to the public, and consulting to coaches and fitness clubs.