Run hard, rest, and do it again. Running intervals should be on the list of every runner’s work out. However, there are numerous styles of intervals and many runners find this confusing.
How hard should you run? How long can I rest? What’s the duration of each session?
Or why should I force myself to sessions where I run out of breath and my legs get sored for days?
For most of my running life, I just follow the plan of running groups and not give too much thought. Now, I want to figure out whether I am running intervals the right way for the most benefit to my body, especially whether it is worth my ache.
I find the act of running intervals to be the toughest, but the most fun and rewarding running training. Knowing how to run intervals will make them even better for you.
I spent weeks going though research papers and comments by runners, and I finally found some satisfying answers which I love to share with you.
In this post, I will use some technical terms such as training zones (1 lowest – 5 highest), effort level, and pace. Most of them will be explained in this post, but more details can be found in my prior post on What Are Training Zones for Runners? The following is a table that summarizes these terms.
Intervals improve cardiorespiratory limits, speed endurance, and muscle strength to boost running performance. Variations of interval speed, length, and rest change the purpose of an interval. By identifying the goal of an interval training, an interval program can be adjusted for best results.
After reading this post, you will understand why we should run intervals, and how we should run intervals for different purposes. I will also share some useful interval workouts for your next running training.
Let’s go!
What Is an Interval Workout?
An interval workout involves multiple sets of hard to very hard effort runs (Work) combined with moderate to very light effort recoveries (Rest).
One example of an interval workout for 5Ks and 10Ks is running 400m (1/4 mile) hard with a 2-minute easy jog, for 10 sets. Alternatively, this could be written as 400m x 10 w/2min rest.
The 400m hard run is the Work and the 2-minute easy jog is the Rest. One session will repeat this Work and Rest non-stop for 10 sets. The 10 sets would take 30-40 minutes.
Hard effort runs build up lactic acid as it involves high levels of anaerobic activity. This lactic acid accumulates, stiffens your muscles, generates the burning feeling, and limits you from continuing.
With recovery, your body gets a chance to flush oxygen through your body to clear your lactic acid so you are able to repeat the hard effort run.
Physiologically, intervals are repeats of lactic acid accumulation and clearance. We use intervals to train our bodies for slower accumulation and faster clearance of lactic acid.
The term “lactic acid” is used for better understanding in the context of running intervals. Technically, it is not fully correct, which I will explain in my future posts. This does not affect the logic in relationship to interval trainings.
Variations of Running Intervals
- adjusting the duration and intensity of the Work (e.g. 100m all out to 8km tempo pace)
- adjusting the duration of the Rest (e.g. Changing Work Time to Rest Time Ratio)
- adjusting the intensity of the Rest (e.g. Standing, Walking/Jogging, Running)
- adjusting the number of sets (e.g. 5 sets to 40 sets)
You can see that intervals can be run in limitless combinations, and it is probably the only type of running training that can utilize runners’ creativity.
Intervals are significantly higher intensity than what your body is used to in day to day life. Remember to always include sufficient warm up and cool down in your sessions to minimize risks of injury.
9 Benefits of Running Intervals
There are 9 major benefits from running intervals that makes it a very attractive workout.
1. Time Efficient
Intervals give you the most bang for your buck. These runs usually last less than 1 hour but its easily more productive than any other type of running training that may take double the time.
This is particularly useful for marathon runners. Intervals can provide workouts that simulate the final miles of a marathon, saving hours of training time.
2. Boost Cardiorespiratory and Anaerobic Limits
The Work part of intervals are your body’s limited chances to test its limit. Without pushing boundaries, your body never knows that it needs to improve its limits.
Running intervals is the major way for a runner to improve cardiorespiratory fitness (VO2 Max) and Anaerobic Limits, resulting in a stronger and faster runner overall.
With proper Rest, each Work set can be pushed to the limit for maximum boost.
3. Improve Speed Endurance
Your body is forced to run at a faster than usual pace for an extended period. With this stimulus, your body will have to learn to transport oxygen to your muscles to create energy more efficiently and sustainably.
As you run more intervals, you will find that you can hold a higher speed longer than before with the help of intervals.
4. Increase Muscle Strength and Stamina
Interval running is the muscle training for runners. You work your muscles (e.g. legs, abs, arms, lungs, heart, etc.) much harder than normal. The extra demand stimulates muscle growth to cater for the harder work.
With stronger muscles and better endurance, your stamina naturally improves.
5. Quicker Body Recovery Capabilities
This is where the Rest part of the interval comes into play. After each hard Work, your body works hard to recover and deliver oxygen to your muscles to clear lactic acid build up.
Intervals limit the time for recovery forcing your body to adapt. With practice, your body develops quicker and more efficient recovery and aerobic capabilities.
6. Promote Proper Form
At a high speed and hard work, your body tries to sprint and run as efficient as possible. With a relatively forward center of gravity at high speed, it is much more difficult to overstride.
Your body’s imbalance and awkward postures also tend to have no place in your sprint, and your body can develop a healthier more efficient running posture.
7. Calorie Burning Efficiency
A Harvard Study reports that more calories per minute is burnt during a higher intensity run.
For a 30-minute run, a 185-pound person burns 733 calories running hard at 6min/mile (3:45/km) but only 444 calories running easier at 10min/mile (6:00/km).
Furthermore, high intensity runs result in additional calorie expenditure from afterburn and reduced calorie intake from lowered appetite.
Double bonus if weight loss is your goal!
8. Enhance Mental Strength
Intervals are challenging workouts and often seem daunting, no doubt. It takes strong mental determination to start the session, and it takes even stronger determination to complete the session.
When you come out the other side, you become so much stronger mentally.
9. Fun
With the many varieties, intervals can be very interesting. It is less boring than a constant speed run, which makes it a bit more fun.
These sessions can also be easily run in a group (and highly recommended). This adds to the social and fun aspect, especially after working hard together.
There are quite a lot of benefits from interval training, and it is one of my favorite types of running. Typically, each interval session should have a minimum of 15 minutes to see the benefits.
Next, let’s talk about how you should run your intervals.
How Hard Should I Run (Work) My Intervals?
The Work part of your interval should be at or above your threshold level of effort. This is the point where you start running anaerobically and your effort level should be hard to very hard. You’ll be barely able to speak a few words during the run.
Out of the 5 training zones, you should achieve zones 4 and 5. For more information about training zones, read my post on What Are Training Zones for Runners?
Now, let’s talk about how hard you should Work for your intervals. It’s quite simple, actually.
The shorter the Work, the faster/harder you run. If it is a 15 second Work, run with a very high effort at your max (high zone 5 level). If it is a 3-minute Work, you would only be able to maintain a threshold speed (zone 4 level).
You’ll be running at as high a speed you can manage to sustain the full session.
So should you Work longer or shorter for your intervals?
This depends on the goal of your session.
For boosting your cardiorespiratory and anaerobic limits, you’ll need to Work hard enough to be running at training zone 5. The quality is more important than the quantity here, and a very hard effort of running needs to be achieved for VO2 Max improvement.
Run short and hard. 10 to 30 seconds may be the longest possible to maintain such a hard level of Work.
For improving your speed endurance, you’ll need to run longer. The idea for speed endurance is to maintain a higher speed longer. The rest time will help increase your total time at a high speed.
This should still be at a training zone 4 effort pushing your threshold speed.
For example, to sustain a 5km run at a high speed, work on five to ten 400m intervals at a slightly faster speed than your target 5km pace (mid-high zone 4). You’ll then be able to build up your speed endurance for your 5km. You would not need to run at max effort in this scenario.
If you are working on a marathon, you might work on 4 sets of intervals as long as 30 minutes long. This would be a marathon pace (lower zone 4) to build up speed endurance for sustaining the full length of a marathon.
Now let’s talk about the Rest portion of your intervals.
How Should I Rest Between Intervals?
Rest Short? Long? Slow? Or Fast?
Taking a Short Rest Between Intervals
A short Rest could be as short as one-sixth of the Work (e.g. 3min Run with 30s Rest) up to equal portions of Rest and Work (e.g. 3min Run/3min Rest) in terms of time.
The short rest keeps the quality and intensity up throughout the session. With limited rest, your recovery is incomplete, and your heart rate stays high before the next set.
This is particularly useful for building up speed endurance and improving your aerobic limits.
If you are struggling with completing a long Tempo, intervals with short Rest are great to break up the tempo as a steppingstone towards the long Tempo work out.
If you are working on maintaining your goal pace for the duration of a race, a short rest can simulate the later sessions of a race in a shorter time for your body to practice sustaining your goal pace.
If you find your running form deteriorate at later stages of a race or long run, short Rest intervals are also useful for practicing form and speed maintenance when fatigued.
If you find yourself getting stiff legs even after a moderate pace, your body might not be sending oxygen through your body quick enough to clear the lactic acid accumulation. The short Rest will train your body to recover quickly, improve your aerobic limits, and run faster and longer with less fatigue.
A popular session of an interval with short rest for 10km training is the 1000m/1min x 6-8 sets.
You’ll run at race pace or slightly faster for 1000m then have a short 1-minute rest (approx. one-third to one-sixth of your Work). This chops the 10km race into more doable sets as you build up towards your 10km race.
Taking a Long Rest Between Intervals
A long Rest could be from equal portions of Rest and Work (1:1) up to six times the work (6:1) in terms of time.
The major benefit of interval training is its time efficiency, so overly long rests become very inefficient if you are just waiting around if your body is already 80% recovered.
Usually the Rest takes no longer than 3 minutes. You are probably not fully recovered, but you are likely recovered enough to repeat very high effort Work.
A long rest encourages the Work portion of your intervals to be as hard as possible. You should be able to complete an interval almost all out yet recover fully before beginning additional repeats.
Quality (effort level) is the focus here, not quantity (time at Work). The idea is to push your boundaries on your Work portion of the rest to boost your cardiovascular limit (VO2 Max), anaerobic limit, and top speed
If you are preparing for a shorter, harder race, intervals with longer rest may be the core of your training.
As you progress and your body strengthens, the rest you need for the same work out can be shortened for best time efficiency.
A popular session for shorter races (3km or under) is running 100m at 95-100% effort (Work 10-20 seconds), then jogging back to the start (Rest 60-90 seconds) for 10-20 sets.
Should You Take Standing Rests Between Intervals?
For beginners, you might only be able to take standing rests as your lungs and heart are already working at their maximum and you are struggling to take an extra step.
Eventually, you will get a choice to stand, walk, or even run during the Rest.
However, standing rests still have their place even for advanced runners in their interval sessions.
Of course, standing rests are necessary for when the rest interval is pitifully short, say 30 to 60 seconds.
Another surprising reason for standing rests is that they make your interval runs harder.
Standing rests don’t allow blood to efficiently flow to the muscles. When you stay standing, your muscles will tighten and make it more difficult to start your muscles again. This is why it is hard to run again after you stopped midway through a race.
For runners who want to train physically and mentally to overcome the “dead” leg feeling that typically happens at the end of a race, you would want to work on intervals with a standing rest.
Marathon runners who don’t want to run 20 miles before approaching the “dead” leg phase can use intervals with standing rest to save time and simulate the “dead” leg push in 30 minutes.
An example would be 2mile/3.2km runs at marathon pace with 2-3 minutes standing, repeating for 3-5 sets. While it looks like an easy session, it takes surprisingly strong mental determination to complete the last set.
Should You Take Walking/Jogging Rests Between Intervals?
This is the most common form of Rest between Intervals. This should be at training zones 1-2 or an easy conversational pace.
Active rest (jogging or walking) is more effective at clearing lactate and preparing you for the next repeat than standing. It keeps the blood flowing to your muscles without adding any additional aerobic stress.
Studies have also found that active recovery was superior to passive recovery for sustaining power output.
Usually, this form is for rest periods between one and three minutes after Working at higher zone 4 to zone 5 intensity for an equivalent or longer time.
Your goal is to catch your breath and get as recovered as possible and make the start of the next set as manageable as possible. This maximizes your speed and effort during the Work portion of your intervals.
An example would be 400m/200m x 10. This is 400m (Work very high effort, roughly 60-90s) with a 200m jog (Rest light to very light effort, roughly 90s-150s), repeated for 10 sets. This is a fantastic work out for improving your maximum speed during 5k/10k races.
Should You Take Running Rests Between Intervals?
The difference in effort between Work and Rest is smaller in these intervals. You will likely be run your Work at a high effort (lower to mid zone 4), and Rest at a moderate effort (higher zone 2 to zone 3).
For some, this may sound pointless for intervals. And true, these sessions aren’t focused on improving your maximum speed.
However, I find intervals with running rests to still be very beneficial, especially during my training for my sub-3 marathon.
These sessions are designed for speed endurance. Your body has to recovery even while it is working during the Rest portion, and then provide even more for the Work portion. Your aerobic capacity improves so you can sustain the higher speed for a longer duration.
By not fully recovering and jogging quickly between repeats you still improve your ability to run at race pace, but you ensure you have the aerobic strength and support to maintain goal pace on race day.
Even for relatively shorter events like the 5k and 10k, endurance is still important for good performance.
Let’s say you are building up towards a new 5km personal best of 20 minutes.
To achieve a constant 4min/km pace for 20 minutes, you might start with intervals of 800m at 4min/km as Work, then 200m at 5min/km as Rest for 5 sets before you can sustain a full 20 minutes at 4min/km.
You are teaching yourself how to run 5k pace with as little rest as possible.
A favorite of mine that is a Running Rest Interval is the Yasso, which I will explain more in the next session.
5 Examples of Interval Sessions
Now that I’ve discussed the intricacies of how to Work and Rest for interval sessions, I’ll give you 5 practical examples of interval sessions so you can take them to use in your run tomorrow.
These can be highly modified (the beauty of intervals) and can be done on a treadmill, track, or side street.
Start with 15 minutes or 4 sets (if applicable) and slowly work your way up. Remember to warm up and cool down sufficiently before and after your run.
If referencing time is difficult, you can use distance, and vice versa.
e.g. As a baseline, a 100m sprint typically takes 10-20 seconds. A 100m running recovery takes two times the sprint time and a 100m walking/jogging recovery takes four times the sprint time.
So a “100m Work, 100m Walking Rest” interval set is equivalent to “15 seconds Work/60 seconds Walking Rest” interval set.
Let’s jump into the examples.
*
5 = Zone 5/Very Hard Effort
4 = Zone 4/Hard Effort
3 = Zone 3/Moderate Effort
2 = Zone 2/Light Effort
1 = Zone 1/Very Light Effort
0 = Standing
*
1. Fartlek
A funny name which is Swedish for ‘Speed Play’. The essence is to run around and vary speeds from very hard effort to light effort without any particular rule.
This can be sprinting between two lamp posts then slow jogging to the next intersection, and so on.
Fartleks are quite fun for group runs. They are also excellent for beginners or runners who haven’t done intervals for a while to acclimatize before tougher forms of intervals.
If you like some structure, here’s a sample.
Run 30s (4-5), Jog 30s (2),
Run 60s (4), Jog 60s (2),
Run 90s (4), Jog 90s (3),
Run 120s (4), Jog 120s (3),
Run 90s (4), Jog 90s (3),
Run 60s (4), Jog 60s (2),
Run 30s (4-5), Jog 30s (2),
Repeat for a total of 2 sets (16 minutes x2)
This is also called a pyramid workout. I find this mentally more manageable than repeating identical sets of 60s Run/60s Rest x 16 for the same effect
2. Track Intervals
This is likely the most common place for interval training. It’s easier to execute an interval session using a standard 400m track with good markings in a relatively controlled environment.
You can repeat sessions after a few weeks and compare to see your improvement.
The runners around you also provide some motivation on these mentally challenging runs.
The variety of interval sessions is limitless.
For boosting your maximum speed, you can do 100m/100m:
Run 100m (5) and slowly jog back to the start (1) for at least 10 sets.
For boosting speed endurance in a 5km, you can do 400m/200m:
Run 400m (4-5) and run easier for 200m (3) for at least 6 sets.
For something in between, you can do 150m/50m:
Run 150m (5) and jog 50m (2) for at least 10 sets.
You could also incorporate pyramids.
Using a Work-to-Rest distance ratios of 2:1, the following is good training for a marathon:
400m(4)/200m(2), 800m(4)/400m(2), 1200m(4)/600m(2), 1600m(4)/800m(2), 1200m(4)/600m(2), 800m(4)/400m(2), 400m(4)/200m(2).
1 set could be good enough (already covers 9600m/6 miles). I have done this several times and there’s a great sense of achievement completing one of these.
3. Hill Intervals
When flat ground is not available, hills become your friend. I live in a hilly area and overtime, I found myself enjoying running up hills than flat ground.
Using hills for intervals can allow you to run a shorter distance for higher effort Work.
Run uphill for 30 seconds with very hard effort (5) then easy jog (1-2) downhill, repeat at least 10 times. This requires a higher effort by your body even at the same pace.
When you improve, you can extend the distance uphill. This is an excellent session for boosting your cardiovascular limits and running efficiency.
4. Yasso
My favorite session during a marathon training.
The name “Yasso” comes from Bart Yasso, the former chief running officer at Runner’s World magazine, who popularized this workout. The essence is 800m intervals with an equivalent time jog recovery.
Work at a hard effort for 800m (4), then Rest at moderate effort for 400m (2-3). Work and Rest should take the same time. Start with 4 sets and slowly add 1 set per week until 12 sets. You could also shorten the Rest slightly for a efficient session.
Yasso is a popular method for marathon training. There are sayings that Yassos can predict your marathon time (I tested this and find it quite true). For example, if you can run 12 sets of Yassos with 3:00 for the 800m run and 3:00 for recovery, you should be able to complete a 3:00 marathon. That’s what I did.
5. High-Intensity Interval Training (HIIT)
HIIT workouts are very popular recently as it is very time efficient for a busy modern day human.
It includes short bursts of intense exercise with a very light intensity recovery. It lasts about 15-30 minutes and is intended to force your maximum effort during the short bursts. You might have seen different versions in CrossFit and cycling.
An example would be an all-out one-minute run followed by a 3-minute recovery, repeated for 5 times.
How to Start Running Intervals for Beginners
As a beginner, jumping into intervals too quickly could increase your risk of injury. A prerequisite would be the ability to run 30-minutes consecutively. I have a guide to achieve this if you are not there yet.
Once you can run 30 minutes consecutively, you can start with easy 30-minute Fartleks but only use slightly harder effort for your Work portion and slight lighter effort for your Rest portion. Build up the intensity difference over time.
Once your body adapts to running with “gear changing”, you can approach other forms of intervals.
Start with 15 minutes, then gradually add time and intensity.
You might need a longer rest in the beginning. This is normal. As you build up recovery capabilities, you can shorten your rest.
1-3 sessions of intervals per week would be sufficient as they are hard to your body both physically and mentally. You need the recovery time after your sessions to minimize your risk of injury.
As intervals are muscle building sessions, eating protein afterwards will help your muscle repair and build up. You can read “Nutrition for Runners” for an idea on other nutritional needs after your session.
Most importantly, enjoy these interval sessions. If lucky, they are great ways to get the runner’s high.
Incorporating Interval Running For Weight Loss
Intervals are very effective for weight loss.
The high intensity increases the calorie burn per minute. Combined with the afterburn bonus, much more calories are expended from an interval session compared to a cardio session using the same time.
In addition, it is found that high intensity sessions reduce the calorie intake from lowered appetite.
1-2 sessions of interval running per week can be beneficial to your weight loss target. I don’t recommend over this number due to injury risks and the mental fatigue that might come from these tough sessions.
Find out more about running and weight loss with my post on Can You Lose Weight By Running?
Conclusion
Intervals are productive and fun work outs that deserve a place in any runner’s training.
While any form of interval session will bring all of the 9 benefits at some level, knowing how to structure your Work and Rest will give extra punch to the particular benefit you are working on.
By knowing how to Work and how to Rest for your interval session, you can modify a similar routine for different purposes. I summarized what we learned in the table below with examples of an equivalent interval set.
| Interval Characteristics | Purpose | Example (Training Zone) |
| Work Short/Very Hard | Boost cardiorespiratory and anaerobic limits | 100m(5)/100m(1) |
| Work Long/Hard | Speed endurance | 800m(4)/200m(2) |
| Rest Short | Speed endurance, improve aerobic limits and recovery capabilities, practice form maintenance while fatigued | 800m(4)/100m(1) |
| Rest Long | Maximize very high effort Work to boost cardiorespiratory and anaerobic limits | 200m(5)/200m(1) |
| Rest Standing | Practice with “dead” legs and the final sections of a long race. May be the only option for beginners or very short rests. | 800m(4)/1min(0) |
| Rest Walking/Jogging | Most effective recovery and maximizes the effects of Work | 400m(4)/200m(1-2) |
| Rest Running | Speed Endurance | 800m(4)/400m(2-3) |
There are times when these intervals become too tough mid-way and you might want to skip a few sets (giving up).
If the effort feels too hard for you to complete the session, adjust the pace of the Work, before changing the Rest. If this is still too hard, extend your Rest before you give up!
A final reminder is to sufficiently warm up and cool down for your interval sessions.
Hopefully, this post about how to run intervals is as beneficial for you as it is for me. I also hope some of your questions are cleared up and you have better knowledge of your interval sessions.
Now please comment your thoughts and share with others if you find this useful.
Then go out, and run your intervals!
Related Reading:
For details about training zone, perceived rate of effort, pace, etc., read my post on What Are Training Zones for Runners?
For details about nutrition to support your run, read The Complete Guide to Nutrition for Runners
If you are running for weight loss, read Can You Lose Weight By Running?
If you want to start running, read How to Become a Runner: A Comprehensive Guide for Your First Two Months
