A Guide to Long Slow Distance (Low-Intensity Cardio)

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Long slow distance training (LSD) is the type of exercise most people associate with cardio. It’s the bread-and-butter of any running program. As certain as the sky is blue and water is wet, if you’ve ever exercised, you’ve done LSD training.

Yet as commonplace as LSD exercise may be, it nevertheless fell prey to the misconception that a good workout could not be a painless workout. And so it was cast aside, as the world enthusiastically embraced the tough-love, feel-the-burn, hard-core workout.1 However, the tide is turning with focus anew on the specific benefits lower intensity exercise brings to the table. Because if you’re interested in doing anything more than a quick sprint, LSD is an absolute, hands-down must do.

But hey, we’ve been through this before. LSD exercise was popularized in the heady, hippy days of the late sixties, as an alternative to the prevailing approach, nicknamed the “PTA school of running” – pain, torture, and agony. Clearly, it was also a good time for funny double entendres.23

What then, is LSD training? As straightforward and self-explanatory as the name sounds, it is more nuanced than simply covering a long distance at a slow, leisurely pace.

What is Long Slow Distance?

Long slow distance means to train at slower than normal race pace for about 30 minutes to 2 1/2 hours, at a steady pace.45 In other words, LSD need not be slow in a leisurely sense or long – “slow” and “long” are relative.

The intensity of LSD training is at a comfortable conversational pace, generally between 60% and 80% of maximum heart rate or 9-12 on the RPE scale.67

The level of exertion of LSD exercise is below something called the first ventilatory threshold (or aerobic threshold), which is the point when breathing suddenly becomes faster and labored, and lactate acid begins to accumulate in the blood.8 Cross it, and you can no longer talk comfortably.9 Many athletes and coaches consider exercise below the first ventilatory threshold to be low intensity.1011 For consistency, we adhere to labelling LSD as low-intensity exercise. However, there are many ways of categorizing exercise intensity and some classifications would describe LSD training as moderate and (at the higher end) even vigorous physical activity.121314

Long slow distance exercise is an essential element in almost any athletes training schedule, though the perhaps less than apt description has fallen out of favor in recent times. Instead, the term LSD is slowly being superseded by a plethora of (less funny) names such as low-intensity steady-state cardio, easy runs, aerobic endurance, continuous exercise training, or some combination thereof.1516 Still, a rose by any other name would smell as sweet.

Why do it?

Benefits of LSD Training

It seems human nature to believe that there is no gain, without pain. Long slow distance challenges that theory. Far from frittering away valuable training time, this low intensity way of training stimulates important and fundamental physiological adaptations.1718

LSD is not a poor man’s HIIT (high intensity interval training). While it shares some of the same benefits as higher intensity exercise, many are unique to LSD training. Moreover, research on competitive and recreational long-distance runners shows that LSD training is associated with better performance and faster finish times.1920 Yet rare is the runner who knows why LSD forms part of their training or its many advantages.

So, here’s a simple overview of the benefits of LSD exercise.

Stronger Cardiovascular System

Long slow distance training strengthens the cardiorespiratory system and causes a variety of changes that improve how much oxygen your body can use during exercise (called VO2 max), boosting endurance performance. It increases how much oxygen is delivered to the muscles and the amount of oxygen they are able to use:21

  • Stronger Heart
    LSD training produces several structural and functional changes in the heart, including improved contractility of the heart, larger blood volume, and increased heart muscle mass and volume. These changes increase the amount of oxygen-rich blood the heart pumps to the body, leading to greater aerobic power and enhanced endurance performance.22232425
  • More blood vessels.
    Alas, it doesn’t matter if your heart is as strong as that of an ox, pumping vast amounts of blood, if it doesn’t reach your muscle fibers. Your heart relies on a network of tiny blood vessels (capillaries) surrounding the muscle fibers to deliver oxygen to your exercising muscles. Low-intensity steady state training develops that capillary blood supply, increasing the body’s capacity of delivering oxygen to the working muscles. These changes are associated with an increase in VO2max and greater exercise performance.26272829
  • Improved ability to take in oxygen.
    In conjunction with increasing maximal cardiac output, LSD improves the ability of muscle to extract oxygen from the blood, allowing for greater delivery of oxygen.30
  • Increased energy making capacity.
    Most of the energy your muscles need during this low-intensity workout is generated by microscopic structures within the muscle fibers called mitochondria. In the presence of oxygen, these infinitely tiny power-plants convert fuel (carbohydrate, fat, protein) into the energy you need to exercise.31

    LSD increases both the number and size of these mitochondria.3233 And the more mitochondria you have, the more energy you can generate during exercise; ergo the faster and longer you can run.

More Key Benefits

Long slow distance training induces other changes that are as, or more important than, a higher VO2max. Other benefits of LSD exercise include:

  • More efficient fat burning.
    The muscles are constantly burning a combination of fat and carbohydrate for energy, to power the muscle contractions needed to move.34 LSD exercise improves the ability of muscles to utilize fat for energy. This is because working muscles are better at getting hold of fat from where it is stored and have an improved ability to burn fat for energy. The greater use of fat as a fuel improves endurance capacity.3536
  • Increased endurance of muscle fibers.
    Regular LSD training changes the characteristics of muscle. The muscle fibers necessary for endurance (slow-twitch fibers) become faster and, with prolonged training, transformation of muscle fibers occurs that makes them more resistant to fatigue:

    Fast-twitch muscle fibers, responsible for strength and short bursts of speed become more endurance oriented by changing subtypes. Some fast-twitch fibers that are very fast and quickly fatiguing (type B) turn into muscle fibers that are slightly slower and more fatigue-resistant (type A). A transition in muscle fibers types may possibly also take place, with fast-twitch muscle fibers turning into slow-twitch fibers. 37383940
  • Higher lactate threshold.
    Low-intensity, steady-state training improves the body’s ability to remove lactate, which increases lactate threshold and endurance performance.4142 This improvement is thought to be due to some of above described adaptations, such as a larger capillary network, more mitochondria, increased fat burning, and changes in muscle fiber types, as well as by other mechanisms.434445
  • Stronger connective tissue.
    Tendons, ligaments, and fascia adapt to the stress of LSD training, strengthening these connective tissues, so that the body is better able to withstand the impact of higher intensity running.46
  • Better running economy.
    LSD exercise improves the efficiency with which the body uses energy and thereby less oxygen at a given speed. In other words, you need less energy to complete your run, which boosts your endurance performance.4748

Function

Purpose of LSD Training

Long slow distance running boasts a laundry list of benefits. But its superpower also lies in the fact that it exerts these benefits with limited stress on the body. While more intense forms of training are possibly able to exert more profound effects in some of the same areas, they are physically and mentally demanding. These workouts require quite a bit of recovery and performing higher intensity exercise most days of the week could compromise performance.49

All these benefits and advantages make LSD a fundamental form of training if you want to improve your race performance. The purpose of long slow distance training is to:

Increase endurance. Running longer, helps you to run longer. The physiological and structural adaptations described above boost endurance.

Develop a base fitness. These beneficial changes increase cardiovascular and muscular fitness, building a solid aerobic foundation that allows runners to safely progress to more demanding types of training such as tempo runs, HIIT, and more race-specific workouts. The better your fitness base, the greater your capacity to run harder and faster.

Facilitate recovery. Allows for active recovery from hard workouts, which is more beneficial than total rest or higher-intensity exercise. It might sound boring and the opposite of the exciting training effects of hard-as-nails workout. But that’s what makes it super important. If your body doesn’t recover, it’s not going to adapt. Active post-workout recovery helps to ensure you reap and build upon the adaptations from hard training, and you’ll feel fresher for the next tough workout.

Improve running form. The comfortable pace allows you to focus on form, improving running technique and efficiency. Faster runs are physically and mentally draining, making it difficult to successfully concentrate on honing running form.

Longer, low-intensity exercise is a foundational building block for all runners:

  • Beginners. The low injury risk and less taxing nature of LSD means means it’s ideal for new runners and those returning from injury, allowing them to build base fitness.
  • Experienced runners. Allows runners to maintain hard-earned aerobic fitness and continue developing running economy. Runners are also able to build training volume with limited stress and without interfering with other, more challenging, workouts.

Workout

Types of LSD Training

There are different types of LSD workouts, each of which are core ways of training that should be part of any running plan.

All are low-intensity performed at a conversational pace.50 The heart rates below are estimates and will vary according to experience and fitness. Also remember to take factors such as heat, terrain, and fatigue levels into consideration, and adjust the distance and pace accordingly. Listen to your body and slow down when you need to.

Many recreational runners have a tendency to run the easy workouts too hard. Monitoring your heart rate during these low-intensity workouts can prevent you from running too fast. This helps to ensure the workouts remain effective and you achieve your goals, as well as reducing the risk of fatigue and overtraining.

Every run serves a purpose. It’s key to achieving your goals, as much as it is to staying healthy and injury-free long-term. There are three main types of LSD workouts, each serves a distinct and important purpose.51525354

The Base Run

Base runs are your average medium-length runs, which are not meant to be challenging, but done often. They are the bedrock of your training. Base runs are also known as easy runs or foundational runs.

The main goal is to increase your weekly training mileage, because it is the total volume of training that stimulates the improvements in aerobic capacity, running economy, and musculoskeletal strength. Base runs are where you can add in extra mileage if you need to reach a particular weekly mileage goal.

How long is a base run

Base runs are roughly 30 to 90 minutes in duration. The precise length of a base run depends on your level of fitness.

Rule of thumb. The distance of a base run is that of your average daily run – give or take an extra mile.

Example: If you run on average 6 miles a day, your base run would be approximately 5 – 7 miles long.

Intensity: Base runs are performed at approximately 70-75% of maximum heart rate (MHR).

The Long Run

Long runs are longest run of the week with the purpose of building endurance and strength, as well as mental toughness and the confidence that you can handle the distance on race day.

While long runs are performed at low-intensity, they are nonetheless hard workouts that leave you fatigued. Limit these workouts to a maximum of one a week or, if you’re prone to injury, fortnightly.

How long is a long run

The length of a long run depends on your level of fitness and your ultimate goal distance (e.g. 5K or marathon).

Rule of thumb. A long run should make up no more than 20 – 30% of your weekly mileage. Also, keep long runs to under 2 1/2 hours (e.g. beginners training for a marathon) to avoid overtraining, burnout, and injury.

Example: If you run 40 miles a week, your long run would be roughly 8 – 12 miles long.

Intensity. Long runs are performed at about 60 – 75% MHR effort. The conversational pace of these runs is comfortable, but they are long and exhaustive. Therefore, avoid the temptation to start out fast. Instead, begin your run at the lower end of intensity, around 60-70% MHR. Once running comfortably, slightly pick up the pace until you’re running at about 75% MHR.

Starting slow and finishing strong has a further advantage; that of knowing you’re in control. The benefits of these runs are as much psychological as they are physical. Long runs increase mental resilience, discipline, and patience.

The Recovery Run

A recovery run is a relatively short run at very easy pace, performed within 24 hours after a hard session (any run that leaves you very fatigued or exhausted, such as a long run or HIIT), before a race, or on those days you’re tired and want to take things down a notch.

Recovery runs are beneficial and a standard part of training. Nonetheless, exactly how they make you a better athlete is not completely clear. Traditional thinking is that these easy runs facilitate recovery by improving blood flow, clearing away lactate, promoting muscle repair, and more.5556

However, recovery runs also allow you to complete more training despite being in a state of lingering fatigue from a previous workout, increasing your total running volume. More importantly, research suggests that because you’re exercising entirely in a fatigued state (which is when the beneficial changes happen and is usually towards the end of a standard workout) this short run triggers many positive adaptations, increasing fitness.5758

How long is a recovery run

Recovery runs tend to be 20 to 45 minutes long. The exact length of a recovery run depends on your level of fitness.

Rule of thumb. The distance of a recovery run is about half the length of your average daily mileage. Generally, keep these run between 2 – 5 miles to maintain their effectiveness.

Example: If you run 6 miles on average, your recovery run would be approximately 3 miles.

Intensity: Recovery runs are performed at an effort level of 60 – 70% MHR. The hallmark of a recovery run is that it is relaxed – run at a very easy pace. This means you can’t go too slow, unless it starts to compromise your running form.

A recovery run should feel like it’s putting in more than it’s taking out. When you’re done you should feel like you had a lot more left in the tank. A good recovery run does not affect the performance of your next workout. Therefore, vary the length of these relaxed runs, if necessary.

Note! Include recovery runs only if you run 4 times a week or more. If you run 3 times a week or less, recovery runs are superfluous. Simply schedule a day off between each run.

One Part of a Greater Whole

LSD is only one weapon in your cardio armory. For it to be most effective combine it with other forms of cardio training, such as HIIT and tempo runs.

Research suggests that an optimal endurance training program for recreational/ amateur athletes consists of a combination of workouts at low-intensity (LSD), moderate-intensity (tempo training), and high-intensity (HIIT).59 The positive effects of higher intensity workouts appear to be maximized when built on a solid base of long, steady endurance exercise.

An exercise program in which LSD workouts forms the bulk of the training in combination with a few higher intensity sessions is associated with increased endurance performance.60616263

Indeed, studies show that elite endurance athletes tend to complete most (roughly 80%) of their training at low-intensity.646566 This approach allows for maximal beneficial adaptions to exercise while minimizing the body’s stress responses and reducing the risk of overtraining.6768


LSD exercise is an essential element of almost any training plan. Long slow distance runs are the foundation on which you build, so that you’ll not just run further, but ultimately also harder and faster.

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