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Intervals Done Right

What’s the difference between 200s and mile repeats? How fast should you run them? How many repeats? How much rest in between? What’s the reason for tempo runs?

Speed work is an important part of most training programs, whether you’re training for your first 5km or latest 100-miler. However, not all speed work is the same, and not all may be right for you. Different types of speed training – different effort levels and lengths – have different benefits for your training. Choosing the right kind depends on your fitness level, what kind of race you are training for, and your own strengths and weaknesses.

You hate running circles around a track? Don’t worry. You don’t have to. Intervals can be done anywhere – road, path, and trail. You don’t even need a watch.

There are different types of speed training, with different purposes/benefits.

From as short as 6 sec up to about 45 seconds. The main purposes of sprints are:

Striders - The first type of speed work all runners should start their season with is Striders. Striders are done at a moderately fast pace, where the focus is on leg turnover, not pure speed. Keep your stride short and quick, uncomfortably so – improvement comes from pushing yourself a little beyond what’s easy or comfortable. Imagine you’re running on hot coals – the harder you hit the ground and longer you spend there the more it hurts – and pick your foot up as soon as it hits the ground.

DON’T REACH! This is important, so let me repeat – don’t reach with your legs! Keep your stride short and make sure your foot lands under your body, not in front of it. It might help to keep your stride short by doing striders on a slight grade, but it shouldn’t be a hard run. It should be easy on the muscles.

Traditionally striders are done on the track, where you sprint the straights and jog the curves. However, then can be done anywhere that’s fairly smooth. Go fast for about 15-30 seconds, or 25-50 strides. Gradually build your speed for the first half, and then maintain that speed to the end. Jog/walk in between for a full recovery, about the same distance, or twice the time.

Striders are good to do early in the season, after several weeks of easy running, and for a few weeks, before starting any hard running. This is also the first, and perhaps only type of faster running new runners should do for their first season. Add them to the middle or end of an easy-moderate short run (i.e., only after a very good warm-up). Start with just 4-6 repeats (a repeat is a round of hard then easy), gradually increasing up to 10-12 over several weeks or months.

Later, as you start hard intervals or tempo runs, striders are a great way to end your warm-up and prepare your body for the harder efforts.

Power Bursts – Very short, 6-10 seconds, hard sprints, preferably up a very steep but still run-able hill. These short sprints engage the fast twitch muscles and begin to introduce a light, quick, efficient stride. Drive your knees up and forward and the arms back forcefully (as if you’re hitting someone behind you in the gut). You can start by taking a few strides in place, to simulate the motion, before driving uphill. Walk back down the hill for a full recovery, ~30-40 seconds.

Hills are preferable because it prevents over striding (i.e., reaching), increases the workload on the muscles, while reducing the stress on joints, bones and connective tissues and the risk of injury. Find the steepest, run-able hill, perhaps around a 10% grade. The specific grade is less important than how it feels. By run-able, I mean not so steep that you have to walk, and not so rocky that you have to alter or think a lot about your stride. Your focus should be on form. Smoother is better. If you have to do this on flat ground, make sure you don’t reach, and plant your foot under your body.

This is a good early season, pre-cursor to longer intervals. New runners probably should avoid them. Do these towards the middle or end of an easy-moderate run. Start with 6-8 repeats, and gradually increase over time. Keep them under 10 seconds; longer is not better.

Hill Sprints – Hard sprints, 20-40 seconds, with a fast and powerful stride, up a steep but still run-able hill. After doing the Power Bursts for a few weeks, you can start adding these longer sprints. These will build more power into your stride, and allow you to carry a faster turnover longer. Go hard, but short of an all-out sprint. Drive your knees powerfully up the hill, and stride quickly. Count your stride rate on a regular moderate run, and strive for 5-10 strides/minute faster (left-right = 1 stride).

Sprint until your legs start to tighten, your form starts to break, and your stride starts to slow – typically around 20 seconds at first – then go just a couple of strides more while working to maintain your form and leg speed. Over time, you’ll be able to increase the amount of time you can hold your form during the sprint, so increase the time accordingly. You should have to work to maintain your form and stride rate at the end, but you shouldn’t feel dead at the end. If your stride breaks down, you’ve gone too far.

Do these towards the middle or end of an easy-moderate effort, short to medium length run. Start with 6 repeats, and increase both the repeats and length of the sprints. Over time, you should be able to maintain your form 40-45 seconds.

Use a slightly less steep grade, around 6%-8%. Again, the feel of the hill is more important than the specific grade.

Short Intervals

1-2 minute hard efforts. The main benefits of short intervals are:

Short intervals are in the 1-2 minute range, about 200m-400m (1 lap on a track is 400m, on the inside lane) for most runners. The hard effort should be at about a 1 mi race pace/effort. A Work:Rest ratio (W:R) of 1:1 (meaning 1 minute easy for 1 minute hard) should give you just enough rest to go hard again, while making the hard efforts increasingly hard but sustainable. If you aren’t able to maintain you speed throughout the workout, then you are running them too hard. Reduce the speed/effort of the hard interval rather than increasing the recovery time.

Short intervals are good for anyone training for shorter races, e.g., 5km-10km, and for those who need to work on maintaining a faster leg turnover at longer distances.

VO2Max Intervals

3-5 min hard, at 15-20 min race pace/effort (e.g., 2mi-5km), W:R 2-2.5:1 (e.g., 5 min hard, 2 min easy). Less fit runners might go a short as 2 min hard, more fit runners up to 6 min. This translates into about 800m (½-mile) to 1-mile repeats.

The main purpose is to stress on your heart, lungs and energy delivery systems. Stress leads to increases in stroke volume, or the volume of blood pumped with each heart stroke. VO2Max workouts can benefit all runners, even ultra-runners. By increasing your stroke volume, your heart can pump more blood, more easily and all effort levels.

The more time spent in the high HR/metabolic zones the better, so keep the rest short. Keeping the rest short allows you to get back to a high heart rate (HR) and metabolic zone quickly. It may take you 4 min to get your HR up on the first interval, but only 30 seconds on subsequent ones. If you allow too much rest, you aren’t getting the proper stimulus.

A variation on this is the Critical Velocity (CV) workout. CV is slightly longer and less hard than VO2Max; 6-9 min hard, 30 min race effort (5km-10km), with a 3:1 W:R ratio. This is a workout that coach Joe Vigil used for Deena Kastor. The theory is that you get much of the max heart stimulus of the VO2Max interval, with less stress on the legs, while also getting much of the lactate stimulus of the tempo workout (below).

Tempo and Cruise Intervals
30-40 min, @ 1hr race effort (10km-20km). A variation of this is Cruise Intervals, 12-18 min hard, 4:1 W:R, 2-4 repeats. The main purpose is to build lactic acid (LA) tolerance. At higher effort levels, your body produces LA. LA is both a byproduct of anaerobic metabolism, and a fuel source. Your ability to run hard, and to maintain a hard effort longer, depends on your ability to process LA back into energy for the muscles.

This is done at or slightly above your lactic threshold (LT). LT is the level at which you produce LA faster than your body can convert it back to energy. The effort level is sometimes called “comfortably hard.” In other words, it’s the hardest effort you can sustain. At LT, you can still talk, perhaps a sentence at a time, needing to stop talking to catch your breath in between, but are no longer able to sing. “Tempo” means a sustained effort.

LT training is best for short to medium distance races that will be run close to or above LT effort; up to ~1:30-2:00 for most runners, and perhaps to marathon distance for fitter runners. It will allow you to run faster before going above LT, and longer at above and slightly sub-LT efforts.

Making it fun

Speed training, like all training, is only good if you do it consistently. If your idea of fun isn’t doing 50 x 400 on the track (how I celebrated my 50th birthday), then you are less likely to do the workout consistently. While the types of workouts described above may be “ideal,” there are ways to make speed training fun, yet still valuable, especially if it gets you to do them.

Skip the track. Use a watch and run the hard/easy intervals by time rather than distance. This can be done anywhere, including your favorite trail. Using time, rather than distance on your rest interval, has the advantage of keeping your from resting too much and limiting your time at the right effort level.

Skip the watch and run fartleks. Fartlek is a Swedish term meaning “speed play.” It typically means using landmarks - e.g., run hard for 3 lamp posts, then easy for 1 – to guide your speed work. Try to pick landmarks that approximate the prescribed times, but it doesn’t have to be exact. Something less than ideal is better than nothing.

Add variety to an interval session. 8 repeats of 800m may be better, but mixing distances in a workout helps to keep if fun and interesting.

Add games with friends. One of my favorites is partner 400s or 800s. Get with someone who’s about your speed – a little faster or slower is OK, but you don’t want one to have too much rest and the other too little. One runs while the other rests, then switch off like a relay. It’s fun to have competitions with similarly combined time teams. Have the faster runners in the pairs start together. For example, I did this with a partner who was running 68 sec 400s against someone doing 69s, and would hand off to me doing 75 sec against someone doing 74. I would start my lap in the lead, then fight to hang on before handing it back to my partner. The competition made us all run a little harder and more consistently than we otherwise would've.

Words of caution

While speed training has tremendous benefits, it’s not without risk. More explosive muscle contractions and longer strides can lead to injury if not done right or too soon. Therefore, follow these guidelines.

Before starting speed work, make sure you have a solid base of running in your legs. For new runners, this may mean several months, or even a whole year of easy running first; I would recommend doing striders after several weeks, but nothing harder until you can sustain an hour+ of running. Then, I might wait a year before doing anything harder than a tempo effort.

Similarly, if you’re coming off an injury or long layoff, ease into speed training first building your legs with easy runs, then striders and sprints before doing intervals.

Don’t overload on intervals. More is not necessarily better. Higher efforts mean greater stress on your muscles, joints, endocrine and immune systems. When you first start doing intervals (from hill sprints to VO2Max), start with only 15 minutes of “hard” efforts (e.g., 10 repeats of 1:30 hard, 1:30 easy, equals 15 minutes of hard effort), maybe only 10 for new runners. Increase it over time, gradually letting your body adapt to higher workloads. At peak, fitter runners might be doing 30-40 minutes of hard effort (e.g., 5-8 x 1mi repeats).

Don’t increase intensity and volume at the same time. Your body has to adapt to changes in training. Too many changes at the same time can lead to injury or illness. When you start adding speed work, slow down or stop the increase in total training volume, or even back off a little. Similarly, when you need to increase your training volume, ease back on the intensity.

Faster is not necessarily better. Run the prescribed effort levels and paces to get the desired stimulus effect. If you aren’t able to sustain your speed throughout an interval workout, then you are running them too hard (or doing too many). It’s better to slow down a little than to extend the rest between intervals.

Don’t leave it on the track. Workouts are not races. You want to finish a workout feeling tired, but that you could’ve gone a little faster, and a little longer. You need to be able to come back the next day.

This is important to remember when running with a group. Use the group to motivate you, but don’t run so hard trying to keep up that you do damage. Run your own pace and don’t get caught up in racing your friends.

Also with a group, don’t let the socializing interfere with the workout. Sometimes it’s easy to start chatting during rest periods and extend the rest too long. This reduces the desired stimulus effect and wastes time. Save the chatting to before or after the workout.

Keep your stride short and quick. Don’t reach with your legs. Speed comes from leg turnover, not from reaching. It may take thinking about shortening your stride – I think of running on hot coals – but as you stride and go faster, your stride length will actually increase.

If you feel any sudden pains or twinges in your muscles or joints, immediately slow down or stop. That may mean that you’re over-extending your stride, that you didn’t warm up enough for the conditions, that your muscles are tired and over-stressed from too much training and/or not enough rest, or that you’re muscles aren’t ready for intervals quite yet. Back off, and try again another day.

Warm up well. Speed puts greater stress on the muscles, so they need to be warmer and looser than when just jogging. The colder it is, the earlier in the day it is, and the longer you’ve been sitting still, the more warm up you need before running hard. On a summer afternoon, you may only need 5-10 minutes of warm-up before starting intervals. However, on a chilly winter morning, just after waking up, you may need 30 minutes or more before you can start sprinting.