In r/AdvancedRunning this week, I saw a question related to Jack Daniels’ Running Formula. I’m a fan of JD, and so I often answer these types of questions to help other runners better understand his training philosophy.
It’s a good question to use to more fully explain how Jack Daniels’ training philosophy works, so I wanted to expand on my answer here.
First, the question (edited for brevity and clarity): I ran a I paced workout based on my current VDOT value, and it felt much easier than a T paced workout based on the same VDOT value. What should I do?
Maybe you’ve had a similar experience – or maybe you just want to better understand how to construct a workout. In either case, keep reading for some thoughts.
Not Familiar with Jack Daniels’ Running Formula?
I’m going to assume here that you have some familiarity with Jack Daniels’ Running Formula – a training philosophy detailed in a book by the same name. If you haven’t read the book, I also wrote up a brief summary here.
In short, JD’s training philosophy revolves around a) doing the least amount of work required to get better and b) focusing each piece of your training on the appropriate pace or intensity.
He breaks runs down into five intensities:
- Easy (E) running, which is conversational and, well, easy
- Marathon (M) running, which is roughly marathon paced tempo
- Threshold (T) running, which is around what you could race for an hour
- Interval (I) or Hard (H) running, which both equate to what you could race for about 15 minutes
- Repetition (R) running, which is roughly the pace you could race a mile.
You can use his VDOT Calculator to plug in a recent race result and generate approximate paces for each intensity of running as well as equivalent race performances at different distances.
The question here really focuses on understanding the structure and purpose of a good Interval / Hard workout.
What Went Wrong For This Runner?
Let’s focus on this particular question first, and then step back and think more generally about how the workout should be structured.
For some additional context:
- The runner logs around 35 mpw (55 km)
- The runner’s T pace is approximately 7:28/mi
- The runner’s I / H pace is approximately 6:53/mi
- The T workout was 5 x 6 minutes T, 1:15 rest
- The I workout was 5 x 800m I (approx. 3:25 to 3:30), with equal rest
Why would the T workout feel appropriately difficult, while the I workout felt easy?
I’d offer two reasons. First, the T workout is objectively harder than the I workout. Second, the I workout isn’t properly structured, and it includes too much rest.
Adjusting Workout Difficulty
If you take any workout, you have a few different things you can adjust to make it easier or harder.
First, there’s the pace or intensity. In this case, the intensity is set by the VDOT value, so we don’t want to change that.
Next, there’s the length of each rep. Keeping everything constant, a workout that’s built on 800m intervals is easier than one built on 1200m intervals. Similarly, 400m intervals is easier than 800m intervals.
You can also manipulate the recovery period. A longer recovery lets you approach the next interval more well rested. That longer recovery interval makes the workout easier.
Finally, you can also adjust the overall volume of work. Holding everything else constant, 30 minutes at T is going to be easier than 40 minutes at T. And that same 30 minutes is going to be harder than 20 minutes.
Re-Examining the Original Workouts
In this case, the T workout is a typical moderate difficulty workout. 30 total minutes of T running is a fairly typical level of volume, unless you’re a high mileage runner. 5:1 rest intervals (one minute rest per five minutes of running) is a normal amount of rest. To make the workout easier, you could make it 5:2. Finally, the length of the rep is more or less typical – 5-6 minutes is a normal, short cruise interval. You wouldn’t want to do shorter reps, but you could make this workout more difficult by instead doing 10 or 15 minute intervals.
To recap: volume is moderate to high; rest intervals are normal; and interval length is minimal. Relative to other T workouts, the interval length is the easiest part here.
In this case, the I workout is very easy. The total volume (5x800m, or 4000m) is on the low end – a typical workout would be 5-6000m. The rest intervals are very generous – 3:30 jog after a 3:30 interval. A ratio of 4:3 or 3:2 would be a more typical rest ratio, and 2:1 would be good for a hard workout. Finally, the reps are on the short end. Typical workouts are usually built around 1000m reps. Given the runner’s pace, 800m reps aren’t horrible – but they aren’t so slow that 1000m (~4:40) reps are out of the question
To recap: this workout is very easy when it comes to rest; easy when it comes to volume; and easy to moderate when it comes to rep length.
So What Should the Runner Have Done?
Objectively speaking, the I workout is much easier than the T workout. So one would expect that the same runner, running both workouts in a short span of time, would feel that the T workout was more challenging than the I workout.
My advice to this runner was to a) increase the volume of his workout to 6x800m and b) reduce the rest time to ~2 minutes. If running on a track, jogging 400m (~2:30) would be ok. But reduce the rest interval in some way.
Why Rest Interval Matters in an Interval Workout
If you ask ten different runners how long you should rest between intervals – you’ll likely get ten different answers. Even Jack Daniels himself will give you different answers, depending on a few factors.
But in Running Formula, he does give us some insight into his philosophy. That’s not to say that it’s the only way to do things. But if you’re trying to structure your training to follow JD’s philosophy, you should understand where he’s coming from.
The I/H intensity is significant because it is the intensity or speed at which you are using the greatest amount of oxygen. Continuing to run at this pace, commonly called VO2 max pace, will help your body adapt to more efficiently use oxygen to improve your speed.
In his research on VO2 max, Jack found that it took a bit of time at the beginning of a rep to get into the zone – and during the recovery period you’d drop out of it. Since running at VO2 max shouldn’t be sustainable for more than 10 to 15 minutes, some amount of recovery is essential to your ability to string together longer workouts. But too much recovery means you’ll miss the mark and do something more akin to a threshold workout.
In the text of Running Formula, Jack suggests that the recovery period is always shorter than the interval period – and the shorter the interval the shorter the recovery ratio. If you’re doing 5:00 reps, the longest he recommends, then you might get closer to a 1:1 ratio. But as you reduce rep length, you should also reduce the interval ratio.
I tend to prefer approaching this running from the “H” perspective – which JD measures in time instead of distance. I usually only do R workouts on the track. So my preferred workouts are 4 minutes work with 3 minutes recovery; 3 minutes work with 2 minutes recovery; and 2 minutes work with 1 minute recovery.
I usually do the 2:1 workouts when I’m coming off a recovery period, and I just want a light workout to get moving. The 3:2 is a typical easy to moderate workout. The 4:3 is a bread and butter hard workout, similar to what you’d expect from a set of 1000m repeats on the track.
But this gives you an idea of what the rest interval should be, depending on how long your rep is. And in the example we looked at above, a 3:30 rest after a 3:30 interval is just too much. This workout should feel easy, because you’re probably going to fully recover between each interval. A recovery interval of 2:00 to 2:30 would be more appropriate.
Bottom Line: Know How to Adjust a Workout to Make it Easier or Harder
At the end of the day, it doesn’t much matter whether you design a “perfect” workout. One of the core precepts of Jack Daniels’ philosophy is that you should do the least amount of work that will allow you to progress. This will help protect you from injury.
If a workout feels too easy, or if you’ve plateaued, then you might want to look at ways to make a given workout more difficult. Add some volume, lengthen your reps, or shorten your rest interval – within reason.
And if a workout feels too hard, you should know how to back things off a bit – reduce volume, shorten your reps, or increase your rest interval – within reason.
Either way, knowing how to pull these levels will help you plan more effectively in the long term.
And if you haven’t picked up your own copy of Jack Daniels’ Running Formula, you should. You really want to make sure you understand the philosophy behind the running plans that you’re using.