There’s nothing like a fast race for leaving a bit of staleness in your legs that detracts from the quality of your quicker workouts.
After having done a 5.5k recovery run on my local hill Monday, I resumed my quest for the 7.5 hour and 90k mark which stands as the goal for week 3 of my “Lydiard Experiment” (the journey to 120k in 9 weeks).
As readers of the Blog may have noticed, Lydiard very much advocates varying the aerobic speeds you run at, so I had a 37 minutes marathon pace (currently 4:10min/km or 6:43min/mile for me) pencilled in for Tuesday.
However, having done a 2k warm-up in my Vibram FiveFingers (review of these later!), my legs felt less than spritely and I decided to make the session a bit easier to ensure I got the right amount of running in at the pace I had planned.
The Aerobic Interval
There’s a misconception that intervals are per definition anaerobic training. They are not: You have two options, 1) You can do sprint intervals which are alactic not anaerobic (e.g. very short) or you can do the 2) Aerobic Interval (generally at marathon and half-marathon pace).
Aerobic intervals must always be much longer anaerobic intervals (following the standard rule that the faster the interval the shorter it must be and viceversa). For novice runners 1k to 1 mile may be good but for developed runners they can be much longer.
I made a quick calculation on what would be the amount of mileage necessary to run around 37 minutes at 4:10 pace and came up with a session consisting of 3 x 3000m @ 4:10 pace. This gives me a target of 12:30 for each 3000m segment.
Aerobic intervals should not use rest periods (passive recoveries) but instead floats (active recoveries) to keep the aerobic stimulus constant and more closely simulate the continuous aerobic run (which is always a better quality session, but can be hard to do with tired legs).
As 3000m is 7.5 laps of the track, I decided to do a 600m float (1.5 laps) to start each repetition at the beginning of a lap. In hindsight, this was probably a bit long as I jogged 600m in around 3 minutes whereas 1-2 minutes recovery would have been more than enough to be fully fresh for me on the night (and in general I would advocate active recoveries of only 30 seconds to 2 minutes for aerobic intervals).
My decision to change the session paid off very well. I started slightly fast and took the first 3000m in 12:09, before slowing down a bit too much and doing the 2nd in 12:34 before taking back the 4 seconds lost doing 12:26 on the third 3000m interval.
This was remarkably stable and shows the benefits of using the track for pace judgement and consistency. The average pace of 4:07min/km was also nice and close to the target of 4:10min/km, meaning I trained exactly the pace I wanted to stimulate on the night. Note that despite my target being close, I did not run to meet target. I ran according to feel (I was looking to a speed that felt slightly slower than my recent half-marathon race pace). I have estimated my TPL based on very good data recently, which is most likely the reason that my projected training pace is so close to my actual training pace. It also highlights that Matt’s system has great merits.
That this type of session can be quite gentle was shown as I easily jogged another 4k as cooldown without being anywhere near fully fatigued at the end. Yet the total mileage for an evening like this was 17k.
My legs are less sore today (recovering from the cross-country), my core is slightly more sore (because running at marathon pace forces you to maintain a better running style than running at recovery and base pace).