Have you seen this, or perhaps experienced it yourself?

Pick a middle or long distance race …  the 1600m … 3200m … 5k … 10k … you choose …

start of race

You are lined up at the starting line …. the starter’s pistol fires …. you take off running ……. your mind goes into a haze ….  you’re feeling good, so you go with the pace …. you tell yourself, “I think I can keep it up” ….. you are able to keep your legs moving, so you keep going for it …..  for a while ….. then, something starts to happen ….. perhaps your chest starts burning …. breathing starts getting a little heavy …. maybe your arms and / or legs start feeling a little rubbery …… you struggle to maintain pace and you start to lose ground … your splits, if they’re being tracked, start to decline … and no matter how hard you try, you just can’t keep the pace …. and your race has gone in the pot!

Exhausted runner taking a breath

The aforementioned is an all too common scenario.

Yes, it is 100% preventable …. and should never happen!

Running is a skill that the athlete must appreciate and develop to race successfully.   Understanding the mechanics of pacing and its relationship to conditioning level, in any race distance, is crucial to one’s running goal achievement, regardless of whether success is defined by a race win or a personal best.

even paced runningSo, while seemingly impractical, and admittedly not easy to learn and put into practice … one of the keys to mid and long distance racing success is pacing … and in the context of this article, I am talking about even split and in some cases negative split pacing.

Simply stated, EVEN SPLIT pacing is running with even or close to even times per respective distance within a race (i.e. preserving 90 second or close to 90 second 400m time for a 6:00 minute 1600m race)

Whereas, NEGATIVE SPLIT pacing is running even or close to even times per respective distance within a race for a component of the race distance and then running faster splits later in the race … perhaps in the critical zone …  (i.e. preserving 90 second or close to 90 second 400m time in the first 75% of a 1600m race and then running sub 90 seconds in the last 400m) … or perhaps running faster times as each split progresses during a race (i.e. 90 … 88 … 85 …. 82)

The question is, how does one achieve even or negative splits?

Well, it’s not easy

It doesn’t just happen without education, training and controlled and purposeful attempt.

But it is possible and is done all the time whether one is a high school, collegiate, age group adult or an elite runner

training planIt takes a combination of the following components:

  1. A conditioning program that promotes and develops the physiological ability to run this way
  2. An understanding of what paces you are capable of, based upon goals and current conditioning
  3. The ability to judge and control one’s pace
  4. The application of a controlled pace

To understand the above three components, an explanation of exercise physiology as it relates to middle and distance running events is essential.

So, put your seatbelt on and let’s go for a little journey


Exercise Physiology 101

ATPBefore we start, the first thing to remember is that ANY muscle contraction or force exertion is due to a molecule, stored in muscle cells, called adenosine triphosphate (ATP)

The body has a limited store of about 85 grams of ATP and will use it up very quickly if our muscles did not have ways of resynthesizing it

The goal of training is to optimize your body’s ability to provide a consistent supply of ATP so as to promote a consistent pace

energy systemsDuring running (and all activity), your body uses 3 energy systems to produce ATP: the anaerobic alactic … the anaerobic glycolytic … and the aerobic energy systems.  Each of these systems work concurrently, with either one being the predominant system depending on the intensity and duration of activity.

In other words, the 3 energy systems do not work in an exclusive sequential manner; each system, either aerobic or anaerobic, work in an overlapping –  perhaps intertwining manner – with one system taking precedence, as stated above, depending on the intensity and duration of the activity


Prior to progressing on to the explanation of each system as it relates to the distance runner, an important priority for the coach and athlete to consider is that training must provide a balanced and periodized plan that incorporates each, without over emphasizing one specific, energy system.  A multi-paced training plan provides the best balance.


ADPThe ANAEROBIC ALACTIC SYSTEM uses ATP, which is already stored in muscle cells, to fuel muscle contraction when you perform an initial burst of activity (i.e. the start of a run, an uphill climb or a surge in a race) or any explosive type activity (i.e. sprinting, throwing, jumping).

ATP stored in the muscles provides energy for about 2 seconds of explosive energy

As muscle cells contract and ATP is broken down, it loses a phosphate molecule and turns into ADP (adenosine diphosphate) … ….it is then resynthesized back into ATP when it gains a new phosphate from the breakdown of a creatine phosphate molecule which is also located in muscle cells.  This process continues until the muscles are depleted of creatine phosphate after about 4 to 6 seconds…..thus allowing about 5 to 8 seconds of sprint or surge ability.

ATP ADPThe working muscles are refueled with ATP after about 3 minutes of rest (an important point to consider when training this system) thus being available for another surge or sprint bout

However, during running, while ATP is resynthesized by creatine phosphate during intense running, thus being available for future sprint or surge activity, concentrations within muscle can be reduced up to 30%.  The degree and speed of availability can enhanced by training

anaerobic glycolysisAs the duration and relative intensity of a run continues beyond the 5 to 8 second surge or sprint, creatine phosphate supplies are depleted and the anaerobic alactic system loses predominance and is eclipsed by the ANAEROBIC GLYCOLYTIC SYSTEM.  In this system, blood glucose and/or glycogen stored in the muscles or liver is broken down to create ATP through the process of anaerobic glycolysis.

The anaerobic glycolytic system is the predominant energy system for all races up to the 400m, as this system prevails (57% anaerobic and 43% aerobic) and is most effective for a period ranging from 10 seconds to approximately 2 minutes


As one approaches the 800m point, the aerobic system has gained prominence as an energy system contributor (66% aerobic versus 34% anaerobic)

Medbo, Tabata, et al, helped provide a newer system of assessing anaerobic capacity through the Maximal Accumulated 02 Deficit Model (AOD or MAOD) (1, 2). This model showed that aerobic and anaerobic energy releases were important throughout the entire effort, and although both increased with duration, the relative importance of the anaerobic system decreased (1). They concluded that, in the 800m, aerobic energy accounted for 40% of the energy release as early as 30 seconds and an equal contribution was found at 60 seconds during the high intensity exercise (1). This contrasted with the earlier research that set the crossover threshold at or after two minutes (1). In addition to providing a new measure of anaerobic capacity, this challenged the existing energetic profiles and demonstrated that energy systems were not utilized in a sequential manner (1, 2).

1  Medbo, Jon Ingulf, and Izumi Tabata. “Relative Importance of Aerobic and Anaerobic Energy Release during Short-lasting Exhausting Bicycle Exercise.” Journal of Applied Physiology 67 (1989): 1881-886. Web.

 2 Medbo, Jon Ingulf, Arne-Christian Mohn, Izumi Tabata, Roald Bahr, Odd Vaage, and Ole M Sejersted. “Anaerobic Capacity Determined by Maximal Accumulated 02 Deficit.” Journal of Applied Physiology 64 (1988): 50-60. Web.


As the athlete progresses towards 1500m, there is an approximate 84% aerobic versus 16% anaerobic contribution in comparison to an approximate 88% aerobic versus 12% anaerobic contribution for the 5k


 aerobic-energy-systemAs identified above, aerobic glycolysis or the AEROBIC GLYCOLYTIC SYSTEM predominates as race distances progress ….. eventually reaching 98% for the marathon distance

During aerobic glycolysis, glucose or fat serve as the energy sources to produce ATP, although with moderate to heavy aerobic activity (as identified above), glucose is the preferred source whereas fat predominates at slower paces of longer duration, such as the marathon

Aerobic glycolysis converts glucose to a pyruvate molecule, within the mitochondria, eventually leading to the production of ATP.

 tired runner13Mitochondria are organelles, found in large numbers in every cell type (except red blood cells), in which the biochemical processes of respiration and energy production occur; these organelles play a dominant role in production of ATP


  • Aerobic glycolysis results in the release of hydrogen ions ….

hydrogen ionsA build up of hydrogen ions will make the muscle cells acidic (normal muscle pH is 7.1) which interferes with the muscle’s ability to contract (a pH reduction to around 6.5 causes such interference) …

and hence ….


tired runner14


Remember now, the aerobic system is still predominating, so as to preserve pace, carrier molecules, called nicotinamide adenine dinucleotide (NAD+), remove the hydrogen ions with resultant production of a NADH molecule.

The NADH deposits the hydrogen ion at an electron transport gate located within the mitrochondria where it combines with oxygen to form water…. water is then released by the body during respiration and perspiration

During aerobic running, pace can be maintained as long as the body’s release of hydrogen ions matches its processing, assuming there is a readily available source of glucose to continually promote ATP production.

It is important to note that the volume and size of mitochondria in one’s muscle cells is directly proportional to training and directly influences one’s ability to process hydrogen ions and produce ATP.

mitochondria t shirt

To put it simply, the more mitochondria you have, the more energy you can generate during running, and the faster and longer you can run


  • Therefore, one of the goals of training is to optimally develop the aerobic system‘s ability to perform aerobic glycolysis …ultimately, to produce ATP

When a runners pace exceeds the aerobic threshold (typically around 70% of one’s aerobic capacity), the aforementioned NADH cannot release its hydrogen ion and hydrogen starts to accumulate in the cell…. this is the point when anaerobic glycolysis or the ANAEROBIC GLYCOLYTIC SYSTEM begins.

At this point, pyruvate is produced faster than it can be used aerobically and unused pyruvate splits into LACTATE and hydrogen ions

LACTATE then transports to the liver where it is converted to glucose, which then returns to the muscles and is metabolized to produce ATP


  • The running intensity at which the blood concentration of lactate begins to exponentially increase is called the LACTATE THRESHOLD


  • The point at which the production of lactate is faster than the body’s ability to process it is called the onset of blood lactate accumulation (OBLA) or ANAEROBIC THRESHOLD


  • Maximal lactate steady state is defined as the exercise intensity at the point in which maximal lactate clearance is equal to maximal lactate production is defined as the MAXIMAL LACTATE STEADY STATE and is considered one of the best indicators of performance perhaps even more efficient than lactate threshold

… when you exceed the OBLA (which generally occurs when the concentration of blood lactate reaches about 4mmol/L … where as at rest it is at 1mmol / L), your body becomes less efficient in its ability to process lactate and hydrogen ions as rapidly as it is being produced thus leading to increased acidity in the muscles and a decrease in the availability of lactate as an energy source.

and as occurs with aerobic glycolysis, your muscles do not perform well in an acidic environment as well as with a reduction in ATP as a fuel source

and hence ….

An exhausted runner pauses towards the end of the London marathon




In general, two people with the same aerobic capacity, (VO2 max), the one with a higher lactate threshold will perform better in continuous-type endurance events.

AND …..

While aerobic capacity can be improved to its optimal level, it is limited by genetic determinations whereas lactate threshold, as a percentage of VO2 max, can be increased through training.

 SO …..

While there may be no improvements in maximal oxygen uptake once genetic limitations are reached, increasing the relative intensity or speed at which lactate threshold occurs will improve performance.


In effect, proper training can shift the lactate curve to the right and one is able to run further distances at higher percentages of one’s aerobic capacity!


So, what does all of this mean for the athlete who wants to even or negative split a race?


Well, when you have a fully developed aerobic and anaerobic system, the following points demand consideration and application:

  • Understanding the physiological limitations of the anaerobic alactic system during the early portions of a race fosters insight into the best tactical race plan for the primary race distance
  • Regardless of race distance, once the starter’s pistol has fired, the anaerobic alactic system is the energy system that provides the quickest provision and replenishment of ATP (i.e. energy) thus allowing the athlete to get up to race speed in the first 50 to 60 meters of a race; as the athlete will produce the same, relatively nominal amount of lactate, essentially not affecting performance, in this short distance, it is tactically advantageous to start the race as fast as possible prior to settling into the established race pace
  • Extending the starting sprint beyond the recommended distance that the anaerobic alactic system will support results in too large of a lactate / hydrogen ion surge ultimately hampering the runners primary race rhythm
  • Lack of optimal training of the anaerobic alactic system will kick start the anaerobic glycolytic system prematurely thus elevating lactate levels which will also hamper the athletes’ ability to perform even pacing
  • During the course of a race, as long as the athlete runs within their trained capabilities with consistent and even pacing, a limited creatine phosphate source should be available to allow ATP production or at least be partially regenerated and be ready to use for the final, vital kick to the finish line
  • The appropriate application of aerobic capacity and fractional utilization of aerobic capacity training will allow optimal development of the aerobic component of a race distance so as to spare how quickly one progresses into the anaerobic glycolytic energy system; a careful sequencing and manipulation of Aerobic capacity, Speed Endurance, Special Endurance 1, Special Endurance 2, Intensive and Extensive tempo as well as Aerobic training are crucial; ultimately, the athlete must train to stay aerobic as long as possible by improving one’s ability to run for longer distances at higher percentages of one’s aerobic capacity  (how this is done correctly is a discussion for another day)
  • Train so that the runner places themselves in the desired tactical position prior to the critical zone; sudden bursts or moves to place oneself in the lead too soon can lead to straying from the trained pace.  Making sudden bursts uses up limited creatine phosphate reserves and allows for limited or no regeneration, especially in the last half of the race when lactate levels are high and progressively increasing.   
  • Coaches and athletes should appreciate the aerobic and anaerobic energy systems as working throughout the whole race in an overlapping fashion with their relative roles shifting depending upon the intensity and duration of the race; specificity of training necessitates a reflection of this interplay of energy systems
  • Even paced running can occur with an optimal mix and periodized sequencing of training paces within the 3 energy systems, thus allowing the athlete to know exactly what pace they are capable of per respective measured distances within a race (i.e. per 400m , 100m, or perhaps 1600m). The athlete should know what happens if one runs at a pace not trained for; if one is trained to run 72 second 400 meters for a respective race distance (i.e. the 800m, 1600m, 3200m and inadvertently runs a 66 early in the race, lactate and hydrogen ion levels will climb to unmanageable levels.  It’s simple science … it’s going to happen


athlete talking with coach
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Experienced athletes should be aware of the energy systems, their physiological functions, limitations and potential for appropriate race tactics and pacing mechanics.  Coach and athlete should have a discussion of the importance of understanding what paces the athlete is capable of, based upon goals and current conditioning.  Ultimately, the coach and athlete should know the pace one is capable of per lap, per kilometer, per mile of respective race distance  – as a reflection of training – thus allowing even pacing as well as negative split pacing.

athlete wins race