Sometimes the way to get a faster Ironman finishing time can be a little bit counterintuitive. Slowing down can often lead to faster finishes. But surely the best way to finish faster is to swim, ride and run faster? Yes and no. You must balance a number of factors which will effect your ability to maintain your speed, some of which are:

  • Your aerobic efficiency at different work rates
  • Your energy cost at different work rates
  • Your ability to eat and digest food at a given work rate
  • How your work rate effects your core temperature
  • External temperature and weather conditions
  • How your effort level effects your sweat rate
  • How much salts & electrolytes you lose in your sweat
  • How much you can drink at AeT

Lets take a look at some of these variables to see how pacing and effort can affect them. 

  • Your aerobic efficiency at different work rates.

The fitter you are the more power you can produce on the bike or the faster you can run for a given effort. If you liken aerobic efficiency to driving your car then it would be measured in miles per gallon. The harder you drive the more fuel you use.

  • Your energy cost at different work rates.

If by slowing slightly on the bike your energy requirements are being met in part by your fat stores instead of only your glycogen stores then you will need to eat less which will have less of an impact on your stomach. This in turn should mean that you are able to eat and digest what you need more easily.

  • Your ability to eat and digest food at a given work rate

Knowing how much you need to fuel your efforts is one thing, being physically able to eat that amount of sugary food for a dozen hours is quite another. Especially for athletes who don’t eat a lot of sugar but in reality for almost everyone it is challenging to eat and drink nothing except sugar for an entire day without suffering some sort of gastric distress. It’s a very common complaint that an athlete just couldn’t force themselves to eat while racing, their stomach shut down.

  • How your work rate effects your core temperature 

We have all experienced the phenomenon of our bodies “warming up” at the start of exercise or as the intensity rises. We might be shivering at the start of a run on a cold day but within 10-15 minutes our body will be warm or possibly even sweating despite there being no change in external temperature. This rise in core temperature while we are racing comes with a cost. The body sweats to cool itself and we lose a certain amount of salts and electrolytes as well as the fluids as a result. If we are racing for a number of hours this fluid especially needs to be replenished and again this will become challenging if we are racing hard in the heat and sweating a lot. At it’s most extreme, overheating will bring you to a walk or even to a stop.

  • External temperature and weather conditions

The external temperature and weather conditions can have a significant impact on how much fluid and fuel your body needs. It can also affect appetite. In the same way as eating too much sugary food can cause your stomach to shut down, so can heat. Very careful pacing is required in hot or extreme conditions to ensure that you don’t tip your body over the edge which will force you to slow.

Balancing our fuel requirements with how much our body and stomach can handle, how much we can eat and digest is key. If we either use all of our glycogen stores and can’t replenish them quickly enough because we are working too hard, then starting the run depleted will often lead to a slower time overall even if you’ve had a fantastic bike split.
Finding this balance must be done in training.

Practicing nutrition during long Ironman pace intervals in training is the best way I’ve found to learn how much I need to fuel any given effort and also how well my stomach is able to digest food at that work rate.