I recently ran an 8 mile cross country race. It was a brutally hilly 3 lap course and I started out characteristically quickly, keen to get a good position. During the second lap I was gleefully overtaking other runners in short bursts. By the third lap, my form had crumbled, I was being over taken and just about finished respectably. Seeing Sarah Tunstall in the 2015 mountain running championships start ahead and finish in 4th place, again, made me ask myself the question what is the real cost of starting too quickly?
It is well accepted by runners, coaches and sports scientists that starting steady and finishing strong is the preferred way to execute a distance race as opposed to starting quickly and fading by the end. A runner’s ability to do this is achieved by maintaining consistent energy consumption.
However I have never really understood why this is the case. Aren’t energy stores available to runners throughout a race to be accessed at any time? If there is enough total energy available then what is the cost of using more at the beginning than at the end?
By understanding energy systems and their by–products we can get the answer.
For a cross country race of up to 10km, energy production is mainly from the aerobic system with the anaerobic filling the gaps. The aerobic system has a larger fuel supply (oxygen), causes little by-products but takes longer to produce energy (90sec to 2 min from when you start running) where the anaerobic system’s supply is limited, produces more by-products but it is immediate.
Hence that sprint at the start of a race to get a good position and overtaking others in short bursts will lead to use of the anaerobic system, which creates more by products (such as hydrogen ions, lactic acid is commonly misunderstood as being a by-product). As sports scientist Steve Magness explains these by-products inhibit subsequent energy production and eventually lead to fatigue. So the more we stress our energy systems at the start, the less that they can do as time goes on to produce more energy.
By-products do not only limit energy production, but they also amplify how we perceive pain. Our body’s self protection mechanisms which are designed to enable us homeostasis mean that if you suffer pain earlier on in the race you are likely to slow down earlier.
With this understanding I’ve been pacing myself better at races and it’s yielding good results. I hope this article helps other runners to do the same.
 Pg 28 The Science of Running, Steve Magness, 2014.