Jack Daniels is not the whisky. He is an exercise physiologist, two-time Olympic athlete, and the author of Daniels' Running Formula — widely considered the most scientifically grounded training system available to distance runners.
The first time I calculated my VDOT from a race result and looked up the corresponding easy pace, I thought the number was wrong. It was nearly 45 seconds per kilometre slower than I'd been running on my "easy" days. Running that slow felt almost uncomfortable. Three months later, my threshold pace had dropped by 12 seconds/km. The easy runs were the thing I'd been skipping past without understanding.
His method is not based on how elite runners happen to train. It is built backwards from physiology: starting with what the body actually needs to improve aerobic capacity, lactate threshold, and running economy, then designing workouts to target each adaptation precisely.
If you've ever wondered where your training paces come from — or why most plans give you arbitrary numbers that don't match your fitness — this is the explanation.
Who is Jack Daniels?
Jack Daniels (born 1933) competed in the modern pentathlon at the 1956 and 1960 Olympic Games before becoming a coach and researcher. He earned a PhD in exercise physiology and spent decades coaching at State University of New York at Cortland.
His research on VO2max, running economy, and training load produced a unified training framework that has been refined across three editions of his book. Coaches at every level — from Olympic programs to self-coached amateurs — use his methods.
What makes Daniels different from most running coaches is that he starts with the measurement of the individual runner, not a generic template.
The foundation: VDOT
The entire Daniels system is built on a single number: VDOT.
VDOT is a measure of your effective aerobic capacity, derived from your most recent race performance. Unlike VO2max — which requires lab testing — VDOT is calculated from something every runner already has: a race result.
A runner who finished a 10K in 45:00 has a VDOT of approximately 46. That number then determines their exact training paces for every type of workout — not based on effort perception or heart rate zones, but on the physiological demands of each intensity.
This is what separates the Daniels method from generic plans that assign paces like "moderate effort" or "conversational pace." VDOT gives you a number. The number gives you exact paces.
As your fitness improves and your VDOT rises, every pace updates automatically. The system self-calibrates.
The five training intensities
Daniels defines five workout types, each targeting a specific physiological adaptation. Using all five in the right proportions is what produces consistent improvement.
E — Easy pace
Easy pace is the foundation of the entire system. It should feel genuinely comfortable — a pace at which you could hold a full conversation without effort.
Physiological target: Aerobic base development. Strengthens the heart, increases mitochondrial density, improves fat oxidation.
When to use it: Most daily runs, long runs, warm-up and cool-down miles.
Common mistake: Running E pace too fast. Daniels' research shows that the aerobic adaptations from easy running happen at relatively low intensities. Running faster doesn't accelerate them — it just adds unnecessary stress.
At VDOT 50, E pace is approximately 6:10–6:50/km.
M — Marathon pace
Marathon pace is the pace you intend to race your marathon. It is faster than E pace but still metabolically sustainable for several hours.
Physiological target: Fat utilisation efficiency at race pace. Trains the body to spare glycogen and operate aerobically at the specific intensity of your goal race.
When to use it: Long marathon-pace sections during peak training weeks. Not used in every session — it's a specific stimulus for marathon preparation.
At VDOT 50, M pace is approximately 5:05/km.
T — Threshold pace (Tempo)
Threshold pace is the fastest pace you can sustain for approximately 60 minutes in a race. It sits at your lactate threshold — the point where lactate begins to accumulate faster than the body can clear it.
Physiological target: Raising the lactate threshold. This is the single most important adaptation for improving marathon and half marathon performance.
When to use it: Continuous tempo runs (20–40 minutes) or cruise intervals (shorter reps with brief recovery). Daniels recommends approximately 10% of weekly mileage at T pace — not more.
At VDOT 50, T pace is approximately 4:40/km.
I — Interval pace
Interval pace is hard. It is run at the intensity that maximises VO2max stress — typically sustainable for 3 to 5 minutes per repetition, with recovery between efforts.
Physiological target: Improving VO2max — the ceiling of your aerobic system. I-pace sessions are the most physiologically demanding of the five types.
When to use it: Short to medium intervals (400m to 1200m), with recovery jogs of equal or slightly shorter duration. Volume at I pace per session: typically 6–10% of weekly mileage.
At VDOT 50, I pace is approximately 4:10/km.
R — Repetition pace
Repetition pace is fast — run at approximately mile race pace or faster, over short distances (100–400m), with full recovery between efforts.
Physiological target: Running economy and neuromuscular efficiency. R-pace sessions are not primarily cardiovascular — they teach the body to move more efficiently at speed.
When to use it: Short reps with long recoveries (typically 2–3 minutes). Volume per session is low because the purpose is quality of movement, not cardiovascular stress.
At VDOT 50, R pace is approximately 3:48/km.
How the five intensities work together
The mistake most runners make is training too much in the middle — not easy enough on easy days, not hard enough on hard days.
Daniels' system prevents this by assigning each workout to a specific intensity with a specific purpose. Easy runs are genuinely easy. Threshold runs are genuinely at threshold. Interval sessions are genuinely hard. There is no ambiguity.
The distribution across a typical training week looks like this:
| Intensity | % of weekly mileage | Purpose |
|---|---|---|
| E (Easy) | 70–80% | Aerobic base, recovery |
| M (Marathon) | 10–15% | Race-specific efficiency |
| T (Threshold) | ~10% | Lactate threshold |
| I (Interval) | 6–8% | VO2max ceiling |
| R (Repetition) | 4–6% | Running economy |
The heavy weighting towards easy running is intentional and well-supported by research. Most aerobic adaptation happens at low intensity. Hard sessions work because the aerobic base supports them — without the base, interval sessions just accumulate fatigue.
How Daniels compares to Pfitzinger and Hansons
These are the three most cited science-based marathon training systems:
| Daniels | Pfitzinger | Hansons | |
|---|---|---|---|
| Foundation | VDOT (performance-based paces) | VO2max + training load | Cumulative fatigue model |
| Weekly mileage | Flexible (scales to VDOT) | High (70–110 km typical) | Moderate-high (60–90 km) |
| Long run cap | 25–27% of weekly mileage | 35–40% of weekly mileage | 26 km max |
| Emphasis | Intensity calibration | Volume + long run specificity | Running on tired legs |
| Best for | Runners who want exact, science-based paces | Experienced runners with strong base | Runners wanting structured high volume |
| Limitation | Requires honest VDOT from a recent race | Demanding volume for most amateurs | Long run cap feels short to many runners |
None of these is universally better. The right system depends on your current fitness, time available, and race goal. Daniels is particularly well-suited for runners who want precision — exact paces derived from their actual fitness, not generic categories.
Why the Daniels method works for adaptive training
The fundamental advantage of the Daniels system is that it is data-driven from the start. Your VDOT is a measurement, not an assumption. Your paces follow from that measurement mathematically.
This makes the system compatible with adaptive training in a way that template-based plans are not. When your fitness changes — because you had a great race, missed two weeks due to illness, or added strength training — your VDOT can be recalculated and every pace updates automatically.
Static plans give you fixed paces for the whole cycle. If your fitness diverges from the plan's assumptions (and it always does), the paces become wrong. The Daniels system gives you a mechanism to correct them.
Daniels' original research on VDOT and training paces is documented in Daniels' Running Formula (Human Kinetics, 3rd edition, 2014). The physiological basis for each training intensity — including the VO2max response at I pace and the lactate clearance dynamics at T pace — is covered in detail in chapters 3 and 4.
VDOT is the starting point for everything Zarkus calculates. When you enter your most recent race result, your VDOT is computed and your training paces are set from that number — not from a generic template. Every week, as your training data comes in, the plan uses CTL, ATL, and TSB to decide whether to push intensity or pull back, while keeping your paces anchored to where your fitness actually is.
If you want a plan built on this framework, join the waitlist below.
Frequently Asked Questions
What is Jack Daniels Running Formula?
Jack Daniels Running Formula is a science-based training system developed by exercise physiologist and two-time Olympic athlete Jack Daniels. The system is built around VDOT — a measure of aerobic fitness derived from your race performance — which determines exact training paces for five workout intensities: Easy (E), Marathon (M), Threshold (T), Interval (I), and Repetition (R). It is documented in his book Daniels' Running Formula (Human Kinetics, 3rd edition, 2014).
What are the five training paces in Daniels Running Formula?
The five intensities are: E pace (Easy) for aerobic base building at 60–79% max heart rate; M pace (Marathon pace) for fat utilisation efficiency at race pace; T pace (Threshold/Tempo) at your lactate threshold for raising your pace ceiling; I pace (Interval) at VO2max intensity in short hard repetitions; and R pace (Repetition) at mile speed for neuromuscular efficiency. Each targets a specific physiological adaptation.
How does Jack Daniels Running Formula compare to Pfitzinger and Hansons?
All three are science-based marathon systems. Daniels uses VDOT to set performance-based paces and scales flexibly to any mileage level — best for runners who want exact, individual paces. Pfitzinger emphasises high volume (70–110 km/week) and long run specificity. Hansons uses a cumulative fatigue model with a maximum 26 km long run. Daniels is particularly well-suited for runners who want precision without committing to Pfitzinger-level mileage.