Fartlek training mixes speed with easy running in an unstructured way. Here's how it works, why coaches use it, & how to add it to your own training.
In the 1930s, Swedish runners introduced one of the most effective training tools, and its name still makes people laugh. Fartlek means “speed play,” which sums up the method’s playful approach better than any technical explanation.
Swedish national coach Gösta Holmér developed this approach after his cross-country teams repeatedly lost to Finnish runners led by the legendary Paavo Nurmi throughout the 1920s. His solution was to blend speed work and endurance training into a single session, letting runners push hard when they felt ready and ease off when they needed recovery.
This training style helped two of Holmér’s athletes, Gundar Hägg and Arne Andersson, break the mile world record five times between 1942 and 1945, lowering it from 4:06.1 closer to the four-minute mark.
Fartlek running differs from regular interval training by allowing for flexibility. You might speed up at a lamppost or slow down as needed, rather than following a rigid structure. This flexibility distinguishes fartlek from measured, timed track workouts.
Most runners want to know if this relaxed approach actually helps them get faster. Research shows that it does, and the reasons might surprise you.
How Fartlek Training Works
Every fartlek run is unique. The main idea is to add short bursts of faster running into an easy or moderate run. These bursts can last from 30 seconds to a few minutes, and recovery times are equally flexible. For example, you might sprint to the next corner, jog until your breathing calms down, then speed up again when you pass a parked car.
This approach is different from traditional interval training. On the track, intervals usually have set distances, times, and rest periods. For example, a coach might ask you to run six sets of 800 meters at a 3:15 pace with 90 seconds of rest between each. Fartlek skips these strict rules and lets you adjust as you feel.
| Training Type | Structure | Pace Control | Recovery |
|---|---|---|---|
| Fartlek | Unstructured, effort-based | Self-directed by feel | Flexible, based on readiness |
| Track Intervals | Prescribed distances and times | Clock-based, specific paces | Timed rest periods |
| Tempo Runs | Sustained moderate-hard effort | Consistent threshold pace | Minimal until completion |
| Easy Runs | Steady low intensity | Conversational pace | Not applicable |
Fartlek’s flexibility makes it suitable for anyone. Beginners can do short bursts with longer breaks, while experienced runners can include harder efforts and shorter recoveries. Each session is tailored to the runner.
The Physiology Behind Getting Faster
Fartlek training improves speed by prompting the body to adapt to cycles of effort and recovery. Alternating between hard surges and easier running helps the cardiovascular system, muscles, and metabolism become more efficient.
VO2 Max Improvements
VO2 max, a measure of aerobic capacity, is one area where fartlek training has shown benefits. Higher VO2 max generally correlates with better endurance performance. Research on 800-meter runners found their average VO2 max improved after eight weeks of fartlek training. A 2014 study in the International Journal of Physical Education, Fitness, and Sports also reported increased oxygen consumption and lower resting heart rate after 12 weeks of consistent fartlek sessions.
The process is simple. Fast bursts put more stress on your heart and blood vessels than easy running. This stress signals your body to adapt by increasing your heart’s pumping, building more tiny blood vessels in your muscles, and helping your cells use oxygen more efficiently.
Lactate Threshold Enhancement
Your lactate threshold is the point where lactate builds up in your blood faster than your body can clear it. Running above this level becomes more uncomfortable and eventually slows you down. Raising your lactate threshold lets you run faster for longer before you hit that wall.
The National Strength and Conditioning Association notes that fartlek training can raise the lactate threshold and support aerobic fitness. The alternating intensity helps clear lactate during recovery. Running coach Matt Forsman states that fartlek, interval, and tempo training can all improve lactate threshold when performed at the right intensity.
To improve your lactate threshold, aim to run at about 95% to 105% of your threshold pace. Running much faster than race pace during intervals doesn’t help build the qualities you need to keep up faster speeds.
Running Economy
Running economy, or how efficiently a runner uses oxygen, can improve with interval and fartlek training. A 2018 study in Physiological Reports found that 40 days of interval training improved running economy across various effort levels.
Varying pace during fartlek sessions recruits different muscle fibers and helps refine running form. Over time, this can lead to smoother transitions and improved efficiency in training and racing.
What a Fartlek Session Looks Like
A typical fartlek workout has a basic structure but allows you to adjust it to your needs.
| Phase | Duration | Intensity |
|---|---|---|
| Warm-up | 10 minutes | Easy jog |
| Main set | 20-30 minutes | Alternating fast surges and recovery jogs |
| Fast surges | 1-3 minutes each | 70-85% maximum effort |
| Recovery jogs | 2-5 minutes each | Easy, conversational pace |
| Cool-down | 10 minutes | Easy jog |
Most runners should keep the total hard running in the main part of the workout between 15 and 20 minutes. Advanced runners who run more each week can work up to 30 minutes of hard effort.
Coach Greg McMillan, named one of the top distance-running coaches by Runner’s World, suggests doing 10 to 12 one-minute surges, each followed by a one-minute jog, at a pace a bit faster than your 5K race pace. This gives you structure but still keeps the flexible spirit of fartlek.
For recovery between surges, a useful guideline is to set the recovery time to 50-75% of the interval. A 4-minute surge would require a 2-3-minute jog recovery before the next hard effort.
How Often Should You Run Fartlek Workouts?
The National Strength and Conditioning Association suggests fartlek training can be done once per week for approximately 20-60 minutes. For beginners, coaches recommend only one speed session per week, and it should not fall on the day before or after another hard session. More experienced runners can handle 1-2 fartlek or interval sessions per week, with easy days in between.
Even though fartlek sessions feel less structured than track workouts, they still place considerable stress on your body. Most runners respond better to two or even three easy days between hard sessions. Treating fartlek as a demanding workout rather than a casual run helps prevent overtraining and injury.
| Runner Level | Fartlek Frequency | Session Duration | Recovery Days |
|---|---|---|---|
| Beginner | 1 per week | 20-30 minutes | 2-3 days |
| Intermediate | 1-2 per week | 30-45 minutes | 2 days |
| Advanced | 2 per week | 45-60 minutes | 1-2 days |
The Mental Side of Speed Work
Fartlek offers more than just physical benefits. Pushing yourself to keep going when you want to stop builds mental strength that helps during races. The more you practice running with speed changes, the less likely you are to give up when things get tough. Your body is often capable of more than your mind thinks.
Since fartlek is based on effort rather than exact pace, it helps you get better at judging your own speed. You learn to handle discomfort without constantly looking at your watch or needing outside feedback. This skill is instrumental in races, where how you feel matters more than any single number.
Studies show that the variety and flexibility of fartlek make it more mentally refreshing than repetitive workouts. Enjoyment is essential for sticking with exercise over time. Because fartlek is self-directed, it can be more appealing than strict interval sessions, helping you stay consistent.
Does Fartlek Actually Make You Faster?
Research shows that fartlek is an effective way to improve running performance. A review of about 29 studies found that less-active or moderately trained runners improved their time-trial results by about 6% with interval training. Well-trained athletes also saw improvements of about 2%.
Over time, fartlek training makes faster paces feel easier. Practicing at speeds above your usual pace can reduce the effort required to run fast by about 10-20%. This is thanks to better heart and muscle endurance, plus the mental strength you build with practice.
Elite runners everywhere use fartlek in their training. It’s a regular part of training camps for top Kenyan distance runners, showing that fartlek works for both beginners and world-class athletes.
Putting Fartlek Into Practice
If you want to try fartlek, start small. Choose one day a week for your session. Warm up with 10 minutes of easy jogging. Begin with short 30-60 second bursts at a challenging but manageable pace, then jog until your breathing returns to normal. As you get fitter, you can make the bursts longer, shorten the recoveries, and add more hard running.
Fartlek adapts to the runner. Running the same route each week can result in a new workout every time, depending on how you feel. Some days may call for longer recoveries and moderate surges; others may allow for harder efforts and shorter recoveries. The structure is flexible by design.
Improving speed requires steady, consistent training. Fartlek offers a flexible and practical approach for building speed. The coaches who developed this method understood that training can be both challenging and adaptable.
