Science behind the sessions

Why it is that we do certain speedwork sessions as runners? You may be part of a club or group where you grind out your weekly track and speed sessions, but wonder other than a virtuous feeling, what running 200m repeatedly vs running 5 x 1km actually gives you in terms of training benefit? Here I’m going to break down some of the science behind the sessions.

Jack Daniels is the godfather of running theory and his thinking is widely accepted. He breaks down speed sessions into three types based on the intensity (heart rate or Vo2max data) and duration for which they should be run for. I think duration is the most accessible indicator, as not everyone has a heart rate monitor, and even fewer of us know our VO2max, but the majority of us time how long we run for.

For the purposes of this blog I refer to an ‘average runner’ as someone capable of a 25  min 5km, or a 4 hour marathon.


5- 15 minute duration

Why?  This is known as Threshold pace, where your body is still able to efficiently clear one of the by-products of energy production, lactate. If you go over your threshold, you feel the burning sensation in your muscles and often slow down, but by working on developing this level in training, you can run at a faster speed for longer.  Especially useful if you tend to start too quickly and are unable to hold this pace in races.

What session?  You should be able to run for 3-4 miles at this speed, or repeated runs of 5-15 minutes each.  For a regular runner, this would mean that 1mile repeats (completed in 8mins) were threshold runs.  It is advised that runners should have 1 -3 minutes rest between runs of this duration.

Example – 4 x 1m, with 2 minute recovery between each.


2-5 minute duration

Why? Known as Intervals – these are hard but not all out (save that for the next one). They develop your aerobic power or ability to use oxygen during exercise (Vo2max) which is key for runners of all distances. If you go over 5 minutes in duration, this develops lactate threshold instead (as above).

What session ?  For our average runner 1km and 800m reps should be completed in 03:53 (800m) and 04:51 (1km). Jack Daniels advocates that recovery involves jogging for a similar duration to the effort, however in in my experience most runners are recovered by 3 minutes.

Example – 8-10 x 800m, with jog recoveries of 3 mins after each.


2 minute duration or less

Why?  Known as Repetitions and the fastest of all, they develop speed and running economy – especially the form aspects (high cadence, circular stride and minimal vertical oscillation).  Useful training for runners across all distances, not only those running short distances.  Especially good if you find you have limited finishing speed during or find it hard to change gear.

What session?  For the average runner 200m is doable in 50 seconds, where 400m is 1 min 50secs. The repetitions are short, but the recoveries should be long to ensure that each rep feels no more difficult than the last.  As the emphasis of this workout is on running economy, you should feel relaxed and like you are able to sustain your form whilst running them.  Be aware that if you run short efforts without feeling fully recovered you are working more on your speed-endurance than your pure speed.

Example – 30 x 200m, ensuring you feel recovered after each.  Break down the 30 as 3 sets of 10.


Hopefully you’ve found this useful to understand more about the reasons behind why we do different types of training and the benefits it can have for you. If you have more questions or would like me to design specific speed sessions for you please do get in touch