Negative Split For Your Next Race

Still on Vince Mauri, he started fast at the Chicago marathon and then dropped a 14:28 min 5 km split (2:53 min/km or 4:39 min/mile) from 20-25 km. He was on course to run a 2:04 hrs race, enough to break the American record of 2:04:43 hrs. 

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.

To run a negative split, you need to have confidence, patience and a tolerance for initial 'underperformance'. You need to resist temptation to "bank time" early and trust your ability to finish strong. 

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

How To Prevent Fading In Your Next Marathon

Exaggerated "float" phase of the run

You were running really well in your key marathon. You've trained very well, started conservatively despite feeling great hoping to have a strong negative split. You've hit all your target times at each 5 km split that you've written down on your hand.

To your greatest horror, you start to tire in the final miles of the race. Your dreams of a personal best begin to fade too.

What was the fade due to? Was it dehydration? High core temperature or low blood sugar? Apparently, none of the usual suspects according to a paper that studied 40 marathon runners immediately before a race and within three minutes of them finishing the race.

The best predictor of the runners fading was in fact muscle damage.

With each stride you run, your quadriceps and calf muscles contract "eccentrically" (lengthen instead of shorten). The muscles shorten when you push off, but they lengthen whilst you are in mid air in the double swing (or floating phase). See picture below.

This causes an accumulation of microscopic damage to your muscles. It's this eccentric contraction that causes delayed onset of muscle soreness (or DOMs).

The above mentioned study of the marathon runners showed that the eccentric contractions can literally hobble you during the race. Runners whose pace dropped more than 15 percent from the beginning to the end of the race had levels of creatine kinase and myoglobin (both are by products of muscle damage measured in blood tests) 53 and 112 percent higher than the runners who managed to maintain a steadier pace.

When I read the paper, my first thoughts was that the runners who faded did not train enough as those who didn't. However, the researchers suggested that age, running experience and training were not significant enough to explain the differences.

The authors suggested three ways to prevent fading in your next marathon.

Doing your long run close to your target marathon pace is crucial to get your muscles stronger. A 30 km run at or close to your target race pace three to four weeks before to simulate the effort will lessen the chance of muscle damage in the race.

Due to the "repeated bout effect", it will be harder to trigger as much muscle damage once they have recovered. You will need to run harder or faster to trigger similar damage.

The second way to increase your ability to withstand eccentric muscle damage is with weight (or resistance) training. Eccentric lunges and squats of at least 80 percent of the heaviest weight you can lift will help prevent damage to your muscles. Do the weight training twice a week during your training cycle and cut back to once a week when you are tapering for the race.

Be sure to practice downhill running if your race has downhill sections. Running downhill causes lots of eccentric contractions, a sure fire way of triggering muscle damage. Experiment with your stride to find the best way of descending as lightly as possible to minimize the muscle damage.


Reference

Del Coso J, Fernandez De Velasco D et al (2013). Running Pace Decrease During A Marathon Is Positively Related To Blood Markers Of Muscle Damage. PLoS One. 8(2): e57602. DOI: 10/1371/journal.pone.0057602.