Mixing up your training is crucial to improving your performance as a runner. While easy and long runs should make up most of your mileage, targeted speed sessions like fartlek and interval training take your fitness to the next level. 

But what’s the difference between these two popular training techniques? And when should you choose one over the other? This guide will break down the key distinctions between fartlek and interval training and provide tips for utilizing each workout to support your running goals.

What is Fartlek Training?


Fartlek, Swedish for “speed play,” is a form of unstructured speed training. These workouts alternate between surges of fast running and recovery jogging at an easy pace.

A typical fartlek workout might include pickups of 1-5 minutes at 5K to 10K race pace, mixed with 1-3 minutes of recovery after each rep. 

You can run fartleks on trails, roads, or tracks, and also incorporate hills and other variations to build strength. Its fluctuating intensities challenge your body to adapt.

Some key benefits of fartlek training include:

What is Interval Training?

half marathon runner

Interval training refers to workouts broken into short, intense periods of work followed by recovery periods. They are typically structured using timed segments or set distances at prescribed paces. 

An example of an interval workout might be 6 x 800m at a 5K pace with 400m recovery jogs. Or 12 x 30 seconds hill sprints with 90 seconds rest. These workouts drive cardio and muscular adaptations by overwhelming your body’s limits in a controlled manner. 

Some benefits of interval training include:

Key Differences Between Fartlek and Interval Training

While fartlek and interval training are both forms of speedwork, they differ in several important ways:

1. Structured vs. Unstructured Running Training

Fartlek training is flexible and completely unstructured. You decide when to pick up the pace and slow down based on how you feel. There are no set interval distances or times.

On the other hand, Interval training follows a structured workout plan with predefined distances or periods for intense work and set rest/recovery intervals. 

2. Intensity

The intensity during a fartlek workout flows based on your energy and motivation. You pick up the speed as fast as you want and slow down when tired.

However, Interval training aims to hit specific target paces/speeds repeatedly for the entire work interval, allowing fluctuation. You push yourself to maintain the prescribed intensity.

3. Continuous vs. Interval

Fartlek running is continuous, with rolling surges and recoveries in pace throughout the run. There are no distinct work and rest periods.

Interval training alternates intense work intervals with fixed recovery intervals, providing defined periods of stress and relief.

4. Purpose

While fartlek workouts increase speed, their main focus is developing overall strength, coordination, efficiency, and mental stamina.

In contrast, with interval training, you can directly work on specific body systems like VO2 max and lactate clearance. It is also helpful for endurance training.

5. Terrain

Fartlek training adapts well to trails and roads, allowing you to incorporate changes in terrain like hills. However, Intervals are often performed on flat, consistent running surfaces like tracks to enable precise pacing and times.

6. Mental Engagement

The flexibility of fartlek requires constant decision-making and mental focus to continually assess your effort and pick optimal times to surge or slow.

Interval training involves more repetition of set paces and periods, often allowing you to zone out between intense efforts.

In general, intervals push your body intensely toward specific fitness goals, while fartleks use a more varied approach. When used together wisely, they can complement each other and offer valuable benefits.

When to Choose Fartlek Training

Fartlek training can be a great option for specific fitness goals and scenarios. Here are some situations where fartlek is a good choice:

1. Variety in Your Routine 

Fartlek provides more spontaneity and variation than structured workouts, which is ideal if you tend to get bored with repetitive training.

2. Transitioning to Speed Work 

If you’re a long-distance runner starting to incorporate more intense speed sessions, fartlek is an excellent middle ground as you transition.

3. Simulating Race Conditions 

Since fartlek involves fluctuating paces and terrains, it’s great for preparing for races like cross-country, where the pace and terrain constantly vary.

4. Improving Mental Focus

With fartlek, you learn to listen to your body and adjust the pace accordingly rather than just following prescribed times. This boosts mind-body awareness.

5. Good for Beginners

 The flexibility of fartlek can be less intimidating for beginners compared to strict interval training.

6. Fun 

Many runners find fartlek training more engaging and enjoyable than highly structured interval sessions. It breaks up monotonous runs with fun variations. Plus, the freedom to choose your path adds exploration and spontaneity to your run.

Fartlek Running Workouts 

To practice fartlek workouts, try these:

For endurance and speed:

For adapting to terrain:

 When to Choose Interval Training

Also, Interval training can be the right choice for certain scenarios and fitness goals. This includes situations like:

1. Achieving Performance Goals

Interval training allows athletes to target precise times and paces needed for goals in their sport, like sprint times for track athletes or split paces for longer races. The work/rest intervals can be tailored to mimic race conditions.

2. Maximizing Calorie Burn

High-intensity intervals significantly spike metabolism and calorie burn. By going all-out for short bursts and then recovering, more calories are torched in less time than steady-state workouts. This leads to greater fat loss.

3. Breaking Through Plateaus

Plateaus happen when the body gets so efficient at an exercise that it no longer has to adapt. Intervals provide a big shock to the system with exertion level variation that forces continued adaptation. This pushes the body beyond a plateau.

4. Improving Cardiovascular Fitness

The constant fluctuation between high intensity and recovery in interval training places an enormous challenge on the heart and lungs. This overload forces the cardiovascular system to strengthen and improve its capacity.

5. Preferring Workout Structure

Some people thrive on and benefit from the precise organization of interval training, where the timing of intense work intervals and easier rest periods is laid out. This structure can provide motivation.

Interval Running Workouts

For speed development:

For cardio improvement:

How to Combine Fartlek and Interval Training

runners running

While fartlek and interval training differ, both can complement each other within a comprehensive training plan. Here are some tips for combining them:

1. Weekly Rotation

 One simple way is to dedicate specific weekdays to each method. For instance, you could do interval training on Tuesdays, Fartlek on Thursdays, and a long, steady run on the weekend.

2. Training Cycles

Use longer training cycles where you focus on one method for a few weeks and then switch. For example, do 2-3 weeks of interval training followed by 2-3 weeks of Fartlek.

3. Within a Single Session

You can combine structured vs. unstructured running training within a single session. Start with structured interval training. Once you’ve completed the set, finish the run with a Fartlek segment where you play with your speed based on how you feel or certain landmarks.

4. Terrain-Based Approach

Use different terrains to your advantage. For instance, if you’re running in an area with hills, you can use the uphill sections for interval sprints and the flat or downhill sections for Fartlek.

5. Phase-Based Training

During the base-building phases of your training cycle, you might focus on Fartlek to gently introduce speed without strict structure. As race day approaches, you could transition to interval training to hone speed and precision.

6. Recovery and Intensity

 After a particularly intense interval session, a Fartlek run can serve as an active recovery a few days later. It can allow you to incorporate some speed without the rigid structure of intervals.

Ultimately, by combining both running workouts, runners can experience the spontaneous, mentally engaging nature of Fartlek while also benefiting from the structured, high-intensity boosts of interval training. It’s a balanced approach that can prevent boredom and ensure continual progress.

Common Mistakes Runners Make When Doing Fartlek & Interval Training:

To maximize the benefits of your fitness routines while reducing injury risk, avoid these common training mistakes:

1. Not Warming Up Properly 

Jumping straight into high-intensity running without a proper warm-up can lead to injuries and won’t provide maximum benefits.

2. Overtraining

Just because these methods revolve around intensity doesn’t mean they should be done every day. Overdoing it can lead to burnout, ankle pains, and injuries.

3. Ignoring Recovery

Especially in interval training, the rest or low-intensity periods are crucial. They allow for partial recovery, which enables you to maintain a high intensity during the work phase.

4. Lack of Variety

Doing the same intervals or using the same landmarks in Fartlek training can lead to plateaus. It’s essential to vary the duration, intensity, and type of intervals and Fartlek sessions.

5. Skipping Cool-Down 

Just as warming up is essential, cooling down after these high-intensity sessions helps in recovery and prevents sudden drops in heart rate.

6. Misjudging Effort in Fartlek

The unstructured nature of Fartlek training means it’s up to the runner to judge effort. Some might not push themselves hard enough during the “speed play” parts, while others might not take it easy enough during the recovery segments.

7. Being Too Rigid in Fartlek 

The essence of Fartlek is its spontaneity. If you find yourself sticking to very rigid intervals during what should be a Fartlek run, you’re missing out on the essence of “speed play.”

8. Not Listening to the Body

Both training methods require tuning into how your body feels. Ignoring signs of fatigue or discomfort can lead to injuries.

Final Thoughts

Fartlek and interval training offer valuable physiological and mental benefits that directly transfer to race day success. The former builds neuromuscular strength and mental focus through unstructured surges, while the latter targets specific systems using prescriptive work and rest periods.

However, choosing the right training method comes down to individual goals, preferences, and where you are in your running journey. Whatever your choice, the journey to becoming a better runner is deeply personal and rewarding, so select the method that resonates with you and aligns with your aspirations.