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  • Writer's pictureJacob Puzey

Critical Velocity Intervals

One of the most essential, yet most challenging workouts for runners is the TEMPO RUN. Whether it be lack of long stretches of flat terrain without stoplights, high heat, or the inability of the athlete to run at or near their THRESHOLD without going over it, the TEMPO RUN is often a frustrating experience for athlete and coach alike.

Runners tend to run TEMPO RUNS either too fast or too slow, essentially losing the benefits of the workout – to build STAMINA and increase THRESHOLD by working in or just below the red line. While heart rate monitors can be helpful in learning what Tempo EFFORT feels like, not all athletes have access to such technology and most need to take a stepping stone approach to be able to handle a standard 20 minute TEMPO RUN.

Critical Velocity Intervals

One way to prepare for continuous THRESHOLD efforts while producing a similar stimulus is to break the THRESHOLD efforts down into shorter, more manageable segments known as CRITICAL VELOCITY (Tom Schwartz) or CRUISE INTERVALS (Jack Daniels).

Critical Velocity is often described as the pace or effort one could sustain for 30-40 minutes or 30-40 minute race pace/effort. For elites and sub-elites, this might mean 10K -12K pace on the road or the track. For others it might mean 5K or 8K pace or effort. The pace doesn't really matter as much as the effort and understanding where it sits along the Peak Run Performance Color Continuum.

Critical velocity intervals are color coded in reddish orange in our training plans to represent the blend between THRESHOLD and SPEED along the Peak Run Performance Color Continuum.

Critical Velocity Intervals allow the athlete to get in the needed volume of quality running, while providing regular feedback and adequate recovery to allow for sustained efforts. In fact, Critical Velocity Intervals often provide opportunities to cover more ground than the athlete otherwise could at the same pace if running continuously.


Georgetown 400s get their name from the former Georgetown University middle distance program notorious for transforming athletes with shorter distance speed into mid-distance superstars. When they started, many of the athletes struggled to sustain 20 minutes of continuous effort at THRESHOLD effort, so their coach, Frank Gagliano, had them start doing short cruise intervals to help build their STAMINA. They already had SPEED. They just needed to develop the STAMINA to extend it. Georgetown 400s helped them blend their SPEED with ENDURANCE and the results were astounding.

For more information on how to prioritize training to maximize performance gains, please read SPEED VS. STAMINA.

Coach Jacob Puzey running Georgetown 400s in the outside lane. Photo by Shara Giordano.

Nuts & Bolts of Georgetown 400s

Georgetown 400s are run in the outside lane of a track. Each interval begins at the outside lane stagger where you would start if you were starting the 400m dash in the outside lane. Run the entire 400m interval in the outside lane until you cross the finish line.

Track dimensions w/ 400m stagger. Modified image from

Warm Up: 15-20 minutes of EASY running + 3-4 x 20 second STRIDES, and DRILLS

Workout: 6-8 x 400m at CRITICAL VELOCITY PACE (30-40 minute race pace/effort) in outside lane starting at the 400m stagger

Recovery: Walk/jog from the finish line in the outside lane until you get to the start of the outside lane stagger (roughly 30-45 seconds). Then start again.

Cool Down: 15-20 minutes of EASY running

Because CRITICAL VELOCITY or CRUISE INTERVALS are shorter than a typical TEMPO RUN, to get the same stimulus they are usually a few seconds per mile faster than THRESHOLD (one hour race) pace, but not as fast as traditional VO2 MAX INTERVAL pace. What makes them challenging is that the rest intervals are shorter than between VO2 Max intervals - usually about half the time it takes you to run the CRITICAL VELOCITY/CRUISE INTERVAL.

While this pace may feel slow compared to what most people typically do when they run INTERVALS on the track, the goal is to gradually fatigue the body and still run a few more intervals at THRESHOLD EFFORT while fatigued.

Finish this workout feeling like you could do at least two more intervals at the same pace.

Use the McMillan Running Calculator embedded in Final Surge to determine your pace.

For example, a 4:05 marathoner training to run a 3:45 marathon, would run Georgetown 400s at approximately 2:01-2:05 per 400m repetition.

Do this workout during the BASE PHASE once every two weeks. Add 2 additional Georgetown 400s each time that you do it. Soon, you will be doing more than 5K (12.5x400m) worth of intervals at THRESHOLD effort/pace.

This workout builds STAMINA and helps you stay on pace/effort zone which isn't always possible if you are trying to do a TEMPO RUN on a busy road or trail.

I've personally used this workout in my own training for MARATHONS and ULTRAS and have found them to be beneficial for the athletes with whom I work. I have coached runners (middle distance runners to ultramarathoners) who have built up to 40 x Georgetown 400s by simply adding one or two 400m intervals per week.

Additional benefits of Georgetown 400s:

INJURY PREVENTION: One of the advantages of Georgetown 400s is that by running in the outside lane you can often avoid the congestion of the inside lane while putting less stress on the inside and outside of your legs by not turning so tightly.

PRACTICE FUELLING: An additional benefit of Georgetown 400s is that they provide a manageable way to practice fuelling while on the run without having to carry a bottle or drop one off hoping to find it when you get there. By simply placing a water bottle with water or an electrolyte drink on the outside of the track near the finish line you can take a swig or two between intervals. This will not only make the workout more manageable in the heat, it will also help you prepare to fuel during your upcoming race.

For more information on how to practice fuelling for race day, please read "Race Day Fuelling - Keep It Simple."

Variations on a Theme

BUILDING UP: Naturally, if you are getting tired of quarters or simply want to switch things up, you can do the same thing with 800s, 1000s, 1200s, etc. Just follow the paces prescribed in the calculator for CRITICAL VELOCITY/CRUISE INTERVALS (see example above) and give yourself approximately half the total run time to RECOVER before starting the next CRITICAL VELOCITY/CRUISE INTERVAL.

MAKE IT A FARTLEK: If a track is not available or if your goal race surface is not as flat and fast as a track, you can do Georgetown 400s as a FARTLEK by running 6-8 x 2 minutes at CRITICAL VELOCITY/CRUISE INTERVAL pace/effort (30-40 minute race pace/effort) and then jog half the time that you run as recovery between intervals. Increase the number of FARTLEK intervals by 2-4 reps each time that you do it. Do this workout on a surface similar to that of your goal race.

SPEED COMBO: As your training progresses and your STAMINA increases, you can do variations of this workout by adding some speed intervals to the end of the workout. For example, after running 16x400m at Critical Velocity/Cruise Interval Pace (30-40 minute race pace), run 4 x 200m at SPEED pace (5K pace/effort or faster) with a 200m jog recovery.

Jacob Puzey is a multiple time national champion and world record holder who helps athletes from all over the world of all ages, abilities, and ambitions to achieve their goals on all distances and surfaces through

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