It is no secret I'm a huge fan of alternations and similar workouts. Basically an alteration workout is a play on intervals where the rests are run at a quick enough pace to force the overall average pace into the range of a tempo workout. These sessions are the best of both worlds option that incorporate the positives of both interval running. Even more importantly they are more than the sum of their parts. Learning to recover at a quick pace leads to huge gains in aerobic fitness much more quickly than you can get from tempos or threshold intervals.
In this blog I'm going to focus on 5k specific alternations. Now in past blogs I have talked about Australian quarters, http://nateruns.blogspot.com/2014/12/workout-wednesday-australian-quarters.html and 400/400 alternations http://nateruns.blogspot.com/2015/01/workout-wednesday-400400-alternations.html both of these sessions are great for the 5k runner. Those workouts both work for the 5k runner and can be part of your prep. The 5k specific workout we are talking about here is just more directly focused on improving your 5k performance specifically.
For 5k specific alternations you want to run a total of 4 miles. You will run the fast portion of the alternation at your goal 5k pace and the recovery sections at 75% to 85% of 5k pace.
To find your recovery pace take your goal 5k pace per mile or kilometer write it in seconds and multiply by 1.15 for 85% and 1.25 for 75%. Finally convert back from seconds to minutes and seconds. For example if your goal 5k is 15:00 that is 3:00 per kilometer which is 180 seconds per kilometer. That gives you a slow end of 3:45 per k and a fast end of 3:27 per k.
Giving some perspective to those paces for a 5k runner capable of aiming for 15:00 running at 3:45 per k, which is a shade over 6:00 per mile, is a pretty easy thing. It is the fast end of what they would be expected to be running on a training run but it is not a tempo effort at all. 3:27 per K is about 5:30 per mile which is certainly faster than a training run but would be much slower than tempo work they do and with practice they will be able to recover at this pace.
Doing the workout- At the start you will run 400m at 5k pace and take 1200m at the slower pace. So the session would be 4x400m at 5k with 1200m recoveries after EVERY rep including the last one at 75% to 85% of 5k pace. This will be 4 total miles. For our example 15:00 runner if he runs his reps at 72 and his recoveries at 85%(3:27 per K/83 per 400m) he will cover the 4 miles in 21:24.
If you can not run the fast end of the recovery zone then your first job is to get faster on the 1200 recovery. So each time you repeat the workout you will still do the 400m at 5k goal pace but each time you will run that recovery faster until you get down to the 85% of race pace range.
Once you reach the point where you can run the 1200 recovery at 85% of goal pace, and for the aerobically well developed among you this will be your first time out, you start increasing your distance at 5k pace and reducing your recovery distance. Each time you repeat the workout you increase the distance at 5k pace by 100 to 200 meters and reducing the recovery by an equal amount.
So you would progress through 4x500/1100, 4x600/1200 up to a goal of 4x800/800 or for someone who is a real workout monster 4x1k/600- this would be 20:16. Which would be a very challenging aerobic test which forces you to relax during your 5k reps as well as your recovery. This is the great advantage of alternations. I can't tell you how often someone tells me they want to run a set time in the 5k and they regularly do 5x1k or even 8 or 10 x 1k at that pace. Heck even 3 or 4 x mile at that pace but they can not seem to hit the time in the race. Why???? The recovery! They are taking too much recovery and they are learning to run repeated races more than learning to run their goal pace at an effort level that makes maintaining it without any recovery for the full 5k possible. The genius of the alternations is that it is focus entirely on teaching you to run your reps at the right effort AND building the aerobic power needed to maintain it for the whole race.