Alex has given me hope when I thought my Ironman race season wouldn’t happen due to chronic Achilles issues.
Declan, London

Interval Running: What to Remember!


There’s a common misconception in runners that ‘the more miles you do, the better runner you become’.  It’s a trap we see people fall into time after time, where training stagnates and becomes a one-dimensional, one pace, slog.

The long, easy/medium intensity runs are certainly important in any training program. The definition of ‘long’ will always depend on the length of your event, but the easy stuff will help to increase your aerobic capacity and give you a decent base level of fitness…but that’s what it is, a base for building speed on top.

Training fuel

Your body has a number of systems that utilise different energy sources to fuel your activity.  These systems overlap, working at the same time, but the intensity of your exercise will determine which system is dominant.

At lower speeds, your body can utilise the oxygen you breathe and fats we store as it’s energy source. This process takes time to kick in and the energy output is fairly low, which is fine for longer, lower intensity training but you’ll run out of gas at higher speeds. This is where the other energy systems kick in to play and give us that extra gear (yes, everyone has an extra gear).

For higher intensities your body uses blood sugar, or glycogen, to give a boost of energy needed to perform at this level. Although the energy output is greater, this process creates lactate as a waste product and can lead to muscle soreness or cramping when the levels get too high.  There’s also a finite amount of glycogen your body can store and use so if we deplete this too much, or cannot replenish it quickly enough, eventually we’ll be trying to run on empty and “hit the wall” as it is termed.

You won’t get fast without training fast

As our whistle-stop tour of the energy systems might suggest, if we don’t train or exercise to a high enough intensity, we won’t cause that switch in dominance to the glycogen-based system.  Without training that system it will remains fairly inefficient and the body will find it a bit of a shock come race-day.

The whole point of interval training is to condition the body into processing blood lactate efficiently, while still exercising. If you can recycle blood lactate well, instead of it accumulating, raising acidity and slowing you down, you’ll be able to break it down and use it as a fuel to keep performing.

The result of this will be a higher lactate threshold, allowing you to perform at a higher intensity before fatigue accumulates!

Depending on your fitness and the distance you are training for, interval sessions may include 5-10 repetitions of a predetermined distance with short rest periods in between.

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