A Basic Guide to Interval Running Workouts

A Basic Guide to Interval Running Workouts

What is Interval Running?

Interval running divides a run into segments at a hard effort with segments of recovery. By dividing the run into hard intervals with frequent breaks at a lower effort, you can sustain more time at the faster pace with less fatigue – resulting in greater adaptation. 

Most runners think of interval runs in terms of distance, such as common track workouts like 10 x 400m. Interval workouts can be structured by distance (800m) or time (3-min). They can be done at a variety of paces (see more below) to elicit different adaptations. You can do them on the track, roads, trails, or hils. 

When done appropriately, interval running can lead to long-term growth and be an enjoyable component in training. When done too hard or too often, interval running can lead to overreaching or burn-out. 

The Anatomy of an Interval Running Workout

Four separate segments typically comprise an interval workout: the warm-up, work intervals, recovery intervals, and cool down. You may have various sets of work and rest intervals at different intensities and durations within a single interval workout. (For more on how to do speedwork effectively, read this article.)

The Warm Up

The purpose of the warm-up is to prepare your body for the higher-intensity running. The warm-up will increase blood flow to the working muscles. The warm-up generally consists of 10-20 minutes of very easy running. The slower, the better! Going too fast in the warm-up is a common mistake that can leave you fatigued by the time the work starts. Start at a shuffle if needed. Near the end, include 2-4 short strides (15-20 second accelerations) to prepare your neuromuscular system for faster running. 

Work Intervals 

The work intervals are the part of an interval run where you run faster. They may be defined by time or distance. For example, if a workout says “5 x 3 minutes”, the 3-minutes are the work intervals (and 5 is the number of repetitions.

Typically, the first interval may feel a bit “harder” or “slower”, as your metabolic rate transitions to a higher contribution of glycolytic energy production and you recruit your fast-twitch muscle fibers. Ease in over the first rep and know that once these systems kick in, you will feel better in the subsequent reps. From there, focus on a consistent effort throughout the entire workout (unless otherwise specified). If you feel good, the final interval can often be slightly faster (but not all-out unless explicitly specified). 

Remember: faster is not better! Every interval workout has a specific purpose. Racing your intervals can counteract the desired physiological adaptations. For most interval workouts, you want to think of leaving one or two reps in reserve; if needed, you could complete one more rep. This approach ensures that you do not deplete yourself on a singular workout. Training is never about one workout; it is about stacking various stimuli and appropriately recovering from said stimuli.

Recovery Intervals

These are the rests in between intervals. The purpose of recovery intervals is to temporarily remove physiological strain so that you can maintain the desired intensity throughout the whole workout. During the recovery intervals, your body clears fatigue-causing metabolites. These metabolites measured by their proxy lactate, but lactate is actually a fuel source. As best as we understand, hydrogen ions, inorganic phosphate, and reactive oxygen species produce fatigue. The recovery interval also lowers heart rate and oxygen consumption rate. 

You might stand, walk, or jog slowly; your workout may specify exactly which one. (And if not, this blog post delves into whether you should stand or jog between intervals.) Your muscle fiber typology may influence how you approach recovery. Those made for endurance can usually recover well with jogging (since they easily recruit slow-twitch fibers), while those made for speed may need to walk to let their fast-twitch muscles rest. 

The biggest mistake runners make is taking these too fast because they try to get a “fast” time for Strava or simply because of lack of experience. Take these at a true shuffle if you do jog them; the slower, the better. 

The Cool Down

The cool down is a bout of easy running after you finish the intervals. The purpose of the cooldown is to gradually transition from work to rest. If you stop immediately after a hard workout, you may feel a bit off, but you won’t hurt yourself. However, a cool down will gradually lower your heart rate, which usually feels better fr most runners than an abrupt stop. 

Go as slow as you need! The cool down should be at an easy effort – and that easy effort may correspond with a slower pace after a fatiguing interval run. If your legs are so fatigued that you struggle with good form, cut it short after 5-10 minutes.

One training theory I have from coaching observation: longer cooldowns may lead to improved fatigue resistance. So while a long cool down is not necessary for an effective interval workout, marathoners and ultra runners may see enhanced fatigue resistance from a cool down lasting up to 2-3 miles. 

The Benefits of Interval Running

Interval running can be a complimentary training stimulus to easy running when appropriately dosed. While easy runs elicit a wide array of peripheral adaptations (mitochondrial biogenesis, angiogenesis, and aerobic enzyme activity), high-intensity interval runs promote central adaptations such as maximum cardiac output and stroke volume. (If you want to learn more, read this 2022 review in Sports Medicine.) Additionally, interval running recruits fast-twitch muscle fibers. When programmed for a runner with adequate training volume, uphill and short intervals may improve running economy, according to a 2014 review in Sports Medicine

Interval running workouts can benefit novice and experienced runners alike. In a 2021 study in the Journal of Strength and Conditioning Research, researchers found a significant correlation between short intervals (200m to 1000m at 95-100% VO2max) and running performance over 3, 5, and 7 years (r=0.56, p<0.001). Considering that the more trained you are, the harder improvements are to come by, the fact that short intervals can improve performance in highly trained runners after seven years indicates their efficacy. (Notably, easy runs and overall running volume had higher correlations with long-term performance.)

Common Types of Interval Workouts

Most interval training for long-distance runners is focused on maximal aerobic power, not anaerobic capacity. 

Hill Repeats:

This type of interval workout involves running short, hard intervals on an uphill gradient. Hill repeats can be on moderate hills or steep hills, depending on desired adaptations and ease of access. You can run them moderate, moderately hard, or hard, with an inverse relationship between duration and intensity. Recoveries are slow jogs or walk back down to where you started the intervals.

Anecdotally, when preparing marathoners, I’ve found that hill repeats performed in the early weeks of training elicit improvements in running economy in both threshold/tempo runs and long runs. The rationale may be multi-fold, but the mechanical stimulus may be a driver of adaptation (more on that training theory in this brilliant article from Trail Runner Magazine)

VO2Max Intervals

VO2max intensity roughly corresponds with 10-15 minute race effort; roughly 5K effort for elite runners or 3K effort for well-trained recreational runners. This intensity still has as significant aerobic contribution. (Even 800m race pace may be as high as 65% aerobic.) It may feel hard, but you shouldn’t finish each interval completely spent. Traditionally, when people talk about interval running, they mean VO2max. But VO2max is not the only factor determining long-distance running performance. These intervals have their place in training, but runners should always be cautious to pace them appropriately. These have rest intervals that are generally 50-100% the duration of the work interval. (Personally, I vary the recovery duration based on factors like heat, altitude, and training phase.)

Critical Speed Intervals:

Sometimes, these can be called threshold intervals. Exercise science and training theory are a crazy world, but generally, critical speed is defined as 20-60 minute race effort -the tipping point where anaerobic energy pathways start contributing more.

In some models, this is classified as “hard” training; other models classify it as “moderate.” It will feel that way – moderately hard for the duration of the intervals. For the sake of simplicity, think of critical speed as what coaches like Tom Schwartz and David and Megan Roche refer to as “30-40 minute race effort”. These are hard, but you aren’t finishing hands on knees. 

Threshold Intervals:

Threshold intervals are typically paced at hour-race effort. In some frameworks, these occur on the same spectrum as critical speed.  intervals. “Threshold” here refers to what popular running literature calls “lactate threshold” but don’t be confused if you encounter a different definition of that term in exercise physiology. 

There are other types of interval runs, such as lactate tolerance intervals. However, these are commonly used for short and middle distance runners (1500m and shorter). 

How often should you include interval workouts in your training?

Interval running workouts should not be a majority of your training. In most training methodologies, interval running compromises no more than 20% of your total training volume. At greater than 20% of your training volume, interval training can lead to diminishing returns and risk overtraining. Too much interval training (or too hard of intervals) done for too long may inhibit certain aerobic adaptations such as fat oxidation. (See more in this opinions article in Frontiers in Physiology.) 

These factors can guide the programming of interval workouts further:

1) Experience level/training history:

Interval workouts place significant metabolic and biomechanical strain on the body. You should have an adequate aerobic base and sufficient musculoskeletal adaptation first. I generally recommend runners spend at least 6-12 months completing just easy runs before they introduce interval running. Newer runners will require more recovery after interval sessions. They may need a complete rest day or cross-training on the day after an interval run. Experienced runners may only require 48-72 hours between interval workouts (but may not do them that frequently based on factors below). 

2) Training intensity distribution.

Training intensity distribution refers to the percentage of runs each week that are easy, moderate, and hard. There are two types of training intensity distributions supported by research and practice: polarized and pyramidal. Polarized features approximately 80% easy/0-5% moderate/15-20% hard. In this model, hard interval running workouts like VO2max intervals will occur frequently. In a pyramidal approach (which is commonly used in endurance training), the distribution is approximately 80% easy/15% moderate/5% hard. Pyramidal training may place more emphasis on threshold and critical speed intervals and less emphasis on VO2max intervals. 

3) Periodization.

Periodization is the concept that training manipulates intensity and volume differently during various phases. Different workouts are used in different phases to elicit particular adaptations. 

In a 2022 review on the training practices of world-class long-distance runners, Haugen et al. that periodization of intervals at hard intensities (above threshold) differs between marathoners and 1500m runners. Marathoners will spend more time in zone 3 (out of 3) in the early preparation period, while the inverse is true for 1500m runners. If you are preparing for a marathon, it’s best to do shorter, faster intervals in the early weeks of training. Any intervals in the 8-10 weeks prior to your race are best done at moderate to moderately hard efforts (under critical speed). You may do VO2max intervals only once a week in the early weeks of training, and then only threshold intervals in the specific weeks leading up to the marathon. 

The inverse is true for 5K races, which have a minor anaerobic contribution during the race. A 2022 study found that when runners progressed from pyramidal to polarized training before their race (doing higher intensity intervals in the weeks leading up to their race), they experienced a significant improvement compared to the inverse group. 

So, a 5K runner may do two interval runs per week (of the same or different types). The marathoner may do one interval workout per week at intensities appropriate to their training phase. 

4) Individual recovery rate.

Genetics, sleep, nutrition, and stress all impact an individual’s recovery rate. Some runners may recover relatively quickly (within 48-72 hours) of an interval workout. Others may need more time to recover. 

5) Individual strengths and weaknesses.

As counter-intuitive as it may sound, a slow-twitch dominant runner may need more hard interval training sessions. A fast-twitch runner targeting a long-distance race may need fewer interval sessions (or a greater emphasis on intervals below critical speed) to elicit desired aerobic adaptations. 

Sample Interval Running Workouts

Interval running workouts can be manipulated by changing intensity, recovery interval duration, number of reps, and work interval duration. These are only a sample of a few types of interval running workouts:

Three Variations of Mile Repeats

VO2max Intervals

Threshold Intervals

Short Intervals within Long Runs

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2 Responses

  1. I am in week 8 of my 16-week marathon training. I just completed an interval workout consisting of a 2-mile warm-up & cool-down, and 10 reps of 400m @ 1:56 w/ 200m recovery. I’m aiming for a sub-4-hour marathon finish.

    I did not hit the 1:56 mark on any of these reps, unfortunately. I stayed between 1:59 for my best and 2:01 for my worst. Should I be concerned that I’m aiming too high for a sub-4 goal based on the results of this workout? Or are these split times close enough to the recommended split time that I’m seeking an achievable goal? Thank you!

    1. Hi! Thank you for commenting!
      There is no direct correlation between 400m rep times and marathon finish time. Slow-twitch runners will have slower short-intervals and faster relative marathon times, compared to intermediate-twitch and fast-twitch runners. Additionally, the energy systems used in 400m repeats differ from those used in the marathon. I wouldn’t use 400m repeats to predict marathon time; marathon pace workouts and threshold runs are better predictors.
      This may be a helpful post: https://lauranorrisrunning.com/marathon-pace-chart/

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