ARTICLE: Mixed Intervals and Peaking Sprints

After my last three articles focusing on the Wicklow Way Trail, I’d like to talk about some of my training methods again. Two days of slow and relatively short hill-running had been on my menu to recover from Saturday’s exertions, so it was time to get the work-clothes on again and do some quality running.

In the past weeks I have moved out of my “Intensity” phase and into two weeks of “Peaking” before a long period, consisting of 10-weeks, that I call simply “Racing”. The nature of training changes radically from Base and Intensity to Peaking and Racing. Basically, you have to accept that the work you have done is done: Your engine is built in the size you wanted and now you just have to polish the chrome. When you’ve then taken the car racing for a while, and it starts to get a bit worn, it’s time to rest and then start building a new and bigger engine. A simple concept, but without the details behind it, also a difficult one to execute.

Three things change in this phase:

1. Mileage drops

2. Intensity of workouts increases

3. Focus shifts from building to maintaining

Two new techniques that I have brought in, mainly inspired by the training methodologies of “Brain Training”-guru Matt Fitzgerald (check out his great blog here) are “Mixed Intervals” and “Peaking Sprints”. Let me talk about them in turn and then give you an example of how I executed my first try at them yesterday.

Mixed Intervals

There are two main types of Mixed Intervals: The “Staircase” and the “Pyramid”. To add to that a “Staircase” can be either “Ascending” or “Descending”. Apart from that no real set format exists but coaches often bring these sessions out simply to add variety and spice to a training programme (and as recent theories are proposing variation and fun can be a very important ingredient in itself to enhance performance).

The key difference between normal intervals and mixed intervals is that the distance covered during you active repetition changes: i.e. instead of 4x800m, you session could be 2x1k, 1x800m, 1x600m. Normally when you run intervals you should focus at running at one steady pace every single repetition and from repetition-to-repetition.

For Mixed Intervals it still applies that you should run your reps steady (e.g. no sprinting at the end etc.) but the pace that you run your intervals at increases as the distance shortens. The final decision to make is how much Recovery (also called “Rest”) or Active Recovery (called “Float”) you should have. When unaccustomed to hard running, 3 minutes is a good start, and you can then move to 2 minutes. Eventually, as you get from Peaking to Racing, you should move down to 90 seconds and 1 minute to make your session increasingly race specific (since you cannot take long breaks in races).

In “Brain Training for Runners “ (Fitzgerald 2009) proposes a “Descending Staircase” session where you move from half-marathon pace to 3000m pace as your intervals grow shorter, and I chose to adopt this format.

I only had 24 minutes allotted this week as I had used up a lot of my “hard quota” on Saturday’s race. So I decided to start with a 1-Mile repeat and work my way down to a 200m. Normally I wouldn't go further down than 600m for a repeat of this type, but as my legs were still tired I thought slightly shorter repeats would benefit my ability to hit my target pace.

The session I constructed looked like this:

Note that I decided to run both the 400m and the 200m at 3k pace (what Icall Zone 7 in my system) to gain a bit more time at this speed with more recovery in between than if I had done a 600m.

And the below is how I ended up running it:

As you can see I started off a bit slow (cautious maybe!) but then remained reasonable close to target especially for the 400 and the 200. Also if you’re doing this remember that the time predictions are for the Track. Yesterday I ran on the trail around the Vartry Reservoir. This loses you quite a few seconds per kilometre, so expect slower times whenever you don’t run on the track compared to your targets.

Despite the naming above, all my recoveries are active as I don’t believe there is any benefit to standing around during a session. If anything you recover faster and better with a slow jog and it’s less of a shock on your body when you go off again.

There’s only 1 rep of each kind here, in Matt’s normal version, you’d do 1-2 reps of the longer intervals (1k-3k distance) and often multiple of the shorter distances (200-400-600-800m). What I do is to simply pick a duration for the session (as above around 25 minutes) and then calculate from there how much I can do. You may prefer to do it the other way around and calculate a distance you want to run and then structure it from there. It really makes very little difference what way you go about it as long as you focus on hitting your target paces while you are doing the session.

How to Pick the Target Pace

I’ve alluded to Matt Fitzgerald’s TPL system many times before which is basically one version of the many systems that predict your race pace on one distance based on the performance on another distance (i.e. using your 10k time to predict your 5k or marathon finishing time).

You can use your recent PBs as a rough guide on how fast to run your sessions. For instance if your 10k PB is 40-minutes then your 10k pace is 4:00min/km. This is a good starting point, as there’s always approx. 5-10 seconds between your 3k, 5k, 10k and half-marathon pace. It’s often easier to simply consult one of the many tables on the topic.

Another way is to simply go by feel: In a normal interval session the effort should feel the same throughout (maybe a bit harder at the end as you tire but not much). In a Mixed Interval the effort should be increase as the distance shortens. I often think that at “half-marathon pace” I should feel “a twinge of discomfort”, at 10k pace “some discomfort, working hard”, at 5k pace “this IS hard!” and 3k pace “auch, won’t last long at this!”. You can make up your own, simply try and remember how you felt the last time you ran one of the classical distances.

If you’re a purist of the hills, there’s nothing stopping you from doing a mixed interval up a slope. Just pick a point ever closer to you and run to it ever faster as you progress. A very simple yet effective session that won’t leave you as devastated as normal hill reps.

In both cases you manage to maintain your body at running at a variety of useful race paces without wearing it by doing too many extended repetitions (say 10x1k session @ 10k pace) or too intense sessions (say a trail-blazing 10x400m @ 1 mile pace).

As a final word on usage, you should combine this type of running with either a more regular interval session, a tune-up race (the Leinster League is great for this) or tempo-runs. The session is great as an additional stimulus and a maintainer of previous gains, but it doesn’t stand alone very well and does not trigger major physiological adaptations to the degree that a regular intervals session will. Add to that a regular interval session will give your body more practice at the speed you are running at while the Mixed Interval is more of a “jack-of-all-trades” workout.

Peaking Sprints

Peaking sprints are very short efforts at absolutely maximal velocity you can crunch out of your body. They force neuromuscular adaptations to max. speed and I like to perform such high-speed workouts after intervals so the body get’s used to finding speed when it’s fatigued while others may argue its better to do it fresh so you can crunch out more speed.

These sprints are shorter than the 200ms that I use in the early stages of the season for speed development which means they are lighter on the body. However, they are performed with very short breaks that mean your heart rate will stay higher than during a standard 200m session.

A peaking sprint only lasts 15 seconds after which you jog for 30 seconds and then you go again. One recommendation is to do these in sets of 5, then jog for 5 minutes and do additional sets. I wanted at least 11 minutes of speed training and had misread the guide, so decided to do 5x15secs with only 20 sec floats, then a 5 minute break, and then a longer set of 10x15sec with 20 sec float.

You don’t worry about pacing here, simply take off like a pistol and keep the foot down. Remember to break gently when the timer goes as the fast braking can be hard on the joints. My greatest surprise in doing this was how quickly I could sprint despite having done the Mixed Intervals and still having Saturday’s race in the legs.

Today my legs feel nice and relaxed as they often do after having done 200s. This suggests to me that this is a great way of “stretching out the legs” after long hard slogs. So for any runner who wants to work a bit on their top speed, have a bit of fun, and loosen up their stride, I recommend finishing key workouts with Peak Sprints during the Peaking and Racing phases of your training.