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What is Critical Velocity?

Critical Velocity or CV training was initially noted in 1960s research as being the highest intensity of exercise one could exert indefinitely without fatigue. This definition has  changed several times over the last sixty years as further research has been conducted.

The general and broad  conclusion is that critical velocity is highly correlated with 10K race effort and that this velocity is significantly correlated with running performances ranging from the 800 meters on up to the marathon.

Research supports the idea that once you begin running at a pace faster than your critical velocity, you will reach VO2 MAX over time.

By training at the critical velocity, one can reach and most importantly, maintain, a high percentage of their VO2 MAX (as well as lactate steady state) for the duration of the individual repetitions of the workout, leading to both VO2 MAX and lactate threshold improvements. Thus, one can view critical velocity as a barometer of aerobic endurance.

Coach Tom "Tinman" Schwartz and Critical Velocity

Running Coach Tom “Tinman” Schwartz is known for the recent popularization of CV training. He believes that that CV is a pace that can be sustained for up to 45 minutes (depending on the athlete’s ability and current fitness).

His research shows that by training an athlete at their critical velocity, they improve their lactate threshold while simultaneously improving their VO2 Max.

The  USATF Coaches Education Program’s % of VO2 MAX method of determining training paces is broken down as follows:

●       800 meters 120-136% of VO2 MAX

●      1500 meters 110-112% of VO2 MAX

●      3000 meter 100-102% of VO2 MAX

●      5000 meters 97-100% of VO2 MAX

●      10000 meters 88- 92% of VO2 MAX

●      Half-Marathon 85-88%% of VO2 MAX

●      Marathon 82%-85% of VO2 MAX

Coach Schwartz believes CV training is about extendibility. His philosophy and goals for his distance runners boil down to extending speed over a greater distance at the same effort as previous workouts. When adding these sessions to a training program, one will be able to improve their fractional utilization of VO2 MAX (the aforementioned 88-92%).

By improving your fractional utilization, you can perform at a faster pace for a longer distance at a lower percentage of VO2 MAX velocity, thereby bringing about improvement across all distances relating to submaximal velocities. Using critical velocity sessions will also allow the runner to go longer and faster at a higher blood lactate concentration level.

In essence, CV training is designed to be a hard, but not-too-hard running pace that improves the aerobic capacity and recruitment of the fast-twitch muscle fibers responsible for endurance and sustainable intermediate speed. These sessions provide high quality work without over-taxing the athlete physically or mentally.

Long-distance runners use primarily slow-twitch muscle fibers (type I). Slow-twitch fibers use oxygen and are more fatigue resistant whereas fast-twitch fibers (IIa and IIx) generate speed but fatigue quickly. Type IIx uses strictly anaerobic energy pathways and lasts only a very short amount of time before fatiguing.

Contrary to conventional thinking, one does not run races even at long distances such as marathons or ultras on slow-twitch fibers alone. Type IIa fast-twitch fibers have properties of both slow-twitch and fast-twitch fibers.

Comparatively, Type IIA muscle fibers can produce higher output than ST fibers, while still using oxygen as their primary energy pathway. CV intervals recruit type IIa muscle fibers which benefit an athlete’s performance in every distance from the 800 to the ultramarathon.

To determine an athlete’s critical velocity, the easiest method is to begin with a recent race or time trial performance. It is best to perform a race or trial effort that is at or near one’s chosen race distance, as this will be more accurate in determining subsequent training paces.

When assigning CV workouts, the coach must assign paces/efforts that are based on their athlete’s current fitness NOT goal times. If the athlete is running based on goal times, the effort becomes closer to full out VO2 Max rather than fractional. Coach Schwartz suggests 6-8% of weekly total mileage can be composed of critical velocity training.

One way to approach this development is with early season intervals structured around CV fartlek runs (after a base period of easy running and some strides), before getting into more event-specific workouts.

Fartleks are essentially time-based intervals, meaning you can do them on variable terrain like trails without worrying so much about specific pace or distance, but rather an effort you could sustain for a specific amount of time.

The beauty of CV workouts is that they can be assigned at just about any point in the training cycle.  For runners competing at longer distances, CV sessions can serve as a sharpening mechanism. For 5K runners, critical velocity workouts can bridge the base building phase and specific training.

Critical velocity training will develop enough fast-twitch fibers to prepare for the demands of specific 5K-pace running. For 5K runners with a finish time in the range of 30-45 minutes, critical velocity will also double as goal pace training. However, for faster athletes, it can serve as an introduction to harder effort running coming off a period of higher mileage that is completed at a less strenuous pace.

For 10K and half marathoners, these sessions serve as a staple throughout the building and even the sharpening phase, as the effort is meant to mimic race pace effort or faster than race (for half marathoners).

Further, shorter critical velocity workouts can build fitness during early season training. As competition approaches, workouts become longer in duration with shorter recovery in between each repetition.

For example, a half marathoner may incorporate sessions consisting of two-mile intervals as they approach their goal race. However, by implementing 800m and 1K CV sessions early in the training cycle, they can improve their threshold prior to beginning the longer sessions specific to the half marathon.

For marathoners, many coaches recommend critical velocity workouts during the earlier weeks of marathon prep (six to twelve weeks prior to the race). Some philosophies include CV intervals through the peak weeks of training, in order to maintain speed without too much fatigue. Reps in CV workouts can range from 2-minutes up to 8-minutes in duration. During peak training, the total volume of the workouts increases.

Even ultra runners benefit from critical velocity as these workouts are known to improve running economy even throughout high volume training. CV sessions are also helpful for trail runners for this reason, specifically if they are completed on the trails rather than roads. Additionally, these types of workouts may prevent mental burnout without causing undo physical fatigue.

Popular Examples of  basic CV workouts

●      8-10 x 2 minutes at CV effort, 2-min recovery jog in between reps;

●      6-8 x 3 minutes at CV effort, 1.5 min easy jog

Another popular method is often referred to as Combo Cruise Intervals. These sessions add short fast intervals at the end of  critical velocity sessions with the goal of  maintaining leg speed without accumulating much fatigue. An example of  this would be  6-8 x 800m at CV pace, with 90-second recovery jog followed by 3 minutes easy and finishing with 4 x 30 seconds fast/30 seconds easy.

As the training cycle progresses and fitness improves, an athlete can decrease recovery time between repetitions,  increase the number of repetitions or increase the speed of their intervals. As the athlete’s ability improves, they should see their ability cruise during a race as well as the distance out they can kick increase. They should also notice that they recover quicker following races or high intensity workouts.

Below are estimated CV paces that correlate between the athlete’s most recent 5K time and the distance of their repetition that they want to run at CV effort:

CV workouts should be used in conjunction with other quality sessions. Just training at critical velocity will make you only good at running at your critical velocity. All types of workouts have value in a well-rounded training plan.

— Andrew Cantor

Chaski Coach Resident Andrew is a former collegiate runner for Salisbury University who competed in cross country and track and field events. He discusses training plans and running philosophies. Aside from running, Andrew is also full-time commercial banker and a biker too!

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