Slow and steady wins the race? Not always. When it comes to pacing in distance running, there are no hard rules, says Mr Ray Loh, an exercise physiologist with Tan Tock Seng Hospital's Sports Medicine and Surgery Clinic.
"It all depends on an individual's fitness level, experience, how they train and their race strategy," says Mr Loh.
Take Patrick Makau's world record setting run at the 2011 Berlin Marathon, for example. The Kenyan achieved his 2hr 3min 38sec timing by starting fast, speeding up, then slowing down in the last 7km or so - though he hung on for the win and record.
In contrast, when Haile Gebrselassie won the race three years earlier (in a then world record time of 2hr 3min 59sec), the Ethiopian started to progressively get faster from the halfway mark. Known as negative splitting, this strategy is typical of most elite runners. Whatever strategy one adopts, pacing is a skill all runners need to learn and master, says Mr Loh.
A pace that is too fast results in fatigue. Mr Loh explains this is because the body uses carbohydrates and fats as the primary fuel source during running, and the faster you run, the more carbohydrates, or glycogen, is used. When these glycogen stores deplete, runners "hit the wall" - that sudden feeling of fatigue and loss of energy in a race or training session.
But running too slow may also cost more energy.
Every runner has an optimal pace at which he can cover the greatest distance with the least effort, according to a study published in the Journal of Human Evolution in 2009.
So how fast should you go?
The best way to find out, Mr Loh says, is through an endurance profiling test to measure your aerobic capacity (VO2 max), lactate threshold and running economy.
Using these indicators, you can find out the safest pace you can sustain without hitting the wall.
Lactate threshold is the point where the lactic acid, a by-product of anaerobic muscle metabolism at high exercise intensities, builds in the muscles due to the body's inability to process it.
This is the "burn" you feel in your legs as you fatigue.
Running economy is a measure of how efficiently a person uses oxygen while running at a given pace. But such tests can easily set one back a couple hundreds of dollars.
A more common and economical way to determine your pace is to regularly run race simulations or timed trials of a given distance. Monitor your pace every kilometre and try to keep it consistent.
During training, work on even pacing.
Your training pace depends on the goal for each session, says Mr Loh.
In general, goals can be categorised into easy run (pace should be slow enough so that you can speak in complete sentences), tempo run and interval run (for these faster runs, you should be able to say a few words before needing to catch a breath).
Modern tools can provide pace feedback to help you stay consistent. The Cruise Control app, launched in January, is particularly useful.
It matches your running footsteps to a musical tempo, cued to your song playlist. It automatically pulls "good running songs" from the music already on the runner's phone into the app.
Set the preferred speed for your run before you head out. During the run, you just need to synchronise your steps with the sound, almost like you are dancing.
The tempo of the sound is automatically adjusted so that you will reach your running goal.
Good pacing comes with experience.
Mr Loh's favourite programme to work on pacing is to do six to 10 repetitions of 1km interval runs on a treadmill at a goal pace, with short 30- to 60-second rests in between sets.
Do not forget to take other factors into account that may affect pace: weather, terrain, elevation, injury and participant numbers.
Once you figure out your pace, remember to stick with it on race day. Runners often get excited or change their game plan at the last minute - a tactical mistake.