However he was running on his own in no man's land, behind the race leaders but in front of his fellow Americans, Clayton Young and Charles Hicks. Then Mauri faltered. He basically tried to bank in time early. Most runners know that the best way to approach a race is to run a negative split. A negative split means running the second half of the race faster than the first half.
Runners know that how you pace yourself at the start is critical in a race, especially in a marathon. If you ran like Mauri, you are doing a positive split, a faster first half of the race followed by a slower second half.
However a review of pacing physiology found negative splits improve glycogen sparing, thermoregulation and cardiovascular drift compared to a fast start. These benefits contribute to delayed fatigue (by sparing glycogen usage) and greater efficiency in the later parts of the race.
If one wishes to race well in a marathon, you need to have enough muscle glycogen. Starting too fast in a race hastens the rate of glycogen breakdown and leads to fatigue inducing metabolites like lactate and hydrogen ions. A negative split pacing strategy allows for more gradual glycogen utilization (since you are going slower) and preserve energy for the later stages of the race.
When you start slower, a higher proportion of your energy are derived from using your fat stores, thus sparing glycogen stores. When glycogen stores are depleted, runners are forced to rely on slower, less efficient energy systems. You experience hypoglycemia-induced fatigue or "hitting the wall".
Glycogen sparing also helps sustain neuromuscular coordination and delay central and peripheral fatigue, both are essential for maintaining biomechanical efficiency in the later stages of a marathon.
This approach is consistenty associated with superior race outcomes (Sha et al, 2024). For example, Eliud Kipchoge's sub-2 hour marathon involved a highly controlled pace with subtle acceleration in the final stages, a textbook example of even to negative pacing.
Remember my post on warm weather making me eat more during my 3 hour Saturday rides? Starting at a conservative pace reduces metabolic heat generation during the early stages as well. Thermoregulation plays a vital role in endurance performance especially in a marathon where progressive effort leads to progressive heat accumulation.
When core temperature rises, the central nervous system initiates protective mechanisms to limit further exertions, known as "central fatigue". A negative split strategy allows for a more controlled rate of heat production early on, helping to delay the onset of thermally induced fatigue.
Moreover, better thermoregulation helps to improve cardiovascular stability. In hot conditions, blood supply is partly directed to the skin for cooling purposes. Meaning your running muscles may not get as much blood flow.
As you sweat more, your blood volume drops causing your heart to beat faster just to maintain cardiac output (or cardiovascular drift). A conservative start minimizes early sweat loss, preserving your blood volume for the final push.
How do you execute a negative split for your race? The authors suggest doing progressive long runs to simulate negative split pacing. Begin at easy pace and gradually increase to race pace or faster in the closing kilometers allowing you to practice the metabolic and mental transition from conservative to assertive effort. Other strategies include tempo runs with a fast finish, negative split intervals and controlled progression runs to develop pacing control and late race strength.
Perhaps using heart rate monitors, GPS pacing, etc is necessary for some runners to achieve pacing awareness.
You can practise visualization, goal setting and self-talk to help reinforce a conservative start and maintain focus before the crucial end part of the race.
Reference
Grivas GV. The Physiology And Psychology Of Negative Splits: Insights Into Optimal Marathon Pacing Strategies. Frint Physiol. 16: 1639816. DOI: 10.3389/fphys. 2025.1639816
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