What Is Fartlek Training? Benefits, Paces & Workouts

Many runners want to add fartlek training to their schedule but aren’t sure how to structure it effectively.

I use fartlek regularly in my own training and have experienced its value firsthand. Because you control the intensity by feel, there is no such thing as a “failed” fartlek session.

This guide covers the training benefits of fartlek, how to set pace and duration, and practical sample workouts.

By the end, you will understand what fartlek targets physiologically and whether it belongs in your training plan.

What Is Fartlek Training?

“Fartlek” is a Swedish word meaning “speed play.”

Alternating Fast and Easy Efforts

Fartlek training means running continuously while alternating between faster and easier efforts. There are no fixed paces, distances, or durations — the approach prioritizes runner feel.

Fartlek does not require off-road terrain. Even on a flat road, alternating between fast and slow running qualifies as fartlek.

How Fartlek Differs from Interval Training

Separating interval training from fartlek training is not always straightforward — both involve alternating hard efforts and recovery periods. The key distinction, if one is drawn, is this:

With fartlek, you manage your own effort level. When things get tough, you ease off rather than pushing through — keeping a degree of reserve throughout the session.

As a result, fartlek is done with some reserve at all times. There is no such thing as a “failed” session because there is no pace to miss.

How Elite Runners Use Fartlek: Kipchoge’s Workout

Fartlek is widely used by elite runners. Here is a sample session from Eliud Kipchoge, the marathon world record holder.

10 min warm-up
10 min × 4 sets (rest: very easy jog 2 min)
※ Target pace: downhill 4:26–4:34/mile (2:45–2:50/km), uphill 5:06–5:14/mile (3:10–3:15/km)
※ Sets 1 and 3 uphill; sets 2 and 4 downhill
15 min cool-down

Eliud Kipchoge – Marathon Full Training Log
(https://www.sweatelite.co/eliud-kipchoge-full-training-log-leading-marathon-world-record-attempt/)

This is one example from the wide variety of fartlek sessions available. Pace and duration shift depending on the training goal.

Below is a sample fartlek session from my own training.

※ Based on Sushiman’s Tinman Workout

How Pace and Duration Shape Your Training Adaptations

The adaptations you get from fartlek depend on how fast and how long you run the hard segments.

The graph below plots blood lactate concentration (y-axis) against exercise intensity, or oxygen demand (x-axis) — effectively, running pace.

By varying the pace and time ratio of your hard and easy segments, you shift the oxygen demand — the exercise intensity — and therefore the training adaptation.

The table below shows the target adaptation, intensity zone, and timing guidelines for each fartlek focus.

Goal	Lactate Threshold (LT)	VO2 Max	Glycolytic Speed / Top-End Pace
Target Pace (Intensity)	75–87% VO2max (marathon pace–threshold pace)	87–100% VO2max (threshold pace–5K race pace)	100%+ VO2max (rep workout pace)
Heart Rate (Reference)	82–89% HRmax	90–100% HRmax	—
Work Interval Duration	3–20 min	45 sec–5 min	30–60 sec
Recovery Duration	10–30% of work interval	50–100% of work interval	200–300% of work interval

Heart rate figures are reference values — they shift with temperature and fatigue. For glycolytic and max-speed work, the long recovery means heart rate does not climb as high during rest.

Because fartlek is often done on trails or hills, flat road race pace is rarely appropriate. Managing intensity by feel or heart rate — covered below — is recommended.

Fartlek Workouts by Goal

Here are sample fartlek workouts organized by training goal.

Improving Lactate Threshold

When the hard segment keeps heart rate in the 82–89% HRmax range, the primary adaptation is lactate threshold improvement. Sample sessions are below. RP indicates a reference race pace for effort calibration.

With enough recovery, even faster efforts stay manageable. This intensity lets you add speed work while keeping overall training load controlled — making it easier to build volume over time.

Boosting VO2 Max

When heart rate in the hard segment reaches 90% HRmax or above, the primary goal shifts to VO2 max development. Breathing becomes noticeably labored during the fast portions.

Fixating on pace at this intensity turns the session into a conventional interval workout. Instead, manage effort by duration, perceived exertion, and heart rate.

Research shows that 30-second efforts with 30-second recovery can sustain time near VO2 max for roughly three times longer than continuous hard running at the same intensity ※2. Brief intervals are enough to deliver a strong cardiovascular stimulus.

Building Glycolytic Speed and Top-End Pace

Efforts above 100% VO2max — faster than 3K race pace — target glycolytic energy metabolism and maximum running speed.

At this intensity, work intervals run 30–60 seconds with recovery two to three times as long.

Three sessions per week of 30-second all-out sprints over seven weeks have been shown to produce statistically significant increases in glycolytic enzymes — both those that break down lactate and those that rapidly oxidize glucose ※3. Speed-focused fartlek is worth including when building top-end pace.

Training Adaptations Aren’t Defined Strictly by Intensity

Fartlek adaptations are not neatly compartmentalized by effort zone.

LT-focused fartlek will also stimulate VO2 max to some degree, and vice versa. The physiological systems overlap.

One of fartlek’s strengths is precisely that you do not have to set pace and duration precisely. That said, some consistency is still worth building in — decide your primary goal and keep the hard segments in the intensity range that supports it.

Pros and Cons of Fartlek Training

Here is an honest look at the benefits and drawbacks of fartlek training.

Benefits

The benefits of fartlek training are as follows.

In distance running, consistent, uninterrupted training matters more than any single workout.

Rigid interval sessions can become impossible on low-energy days, and a failed session means neither the intended stimulus nor training continuity. That frustration compounds over time.

Fartlek lets you control the effort on the fly. Running with reserve reduces the risk of injury and overtraining — a reason I keep it as a regular part of my own schedule.

I genuinely enjoy fartlek. The low-stakes nature makes it easy to look forward to, which is reason enough to keep it in rotation.

Drawbacks

The main limitation of fartlek is that it makes it harder to identify why performance improves.

When a tempo run lifts your half marathon time, you can reasonably attribute it to lactate threshold improvement. The cause-and-effect is clear.

With fartlek, the variable intensity means the actual adaptation can shift from session to session, making cause-and-effect less clear-cut.

Fartlek is versatile, but that flexibility is also a limitation for tracking specific gains.

Freedom is the point — but building some consistency into your fartlek sessions is still worthwhile. Choose a primary goal and keep your hard efforts in the intensity range that targets it.

Tips for Effective Fartlek Training

Here are practical tips for recreational runners looking to get the most from fartlek training.

Choose Traffic-Free Routes

Keeping your legs moving continuously is part of what makes fartlek effective. Choose routes without traffic lights so you are never forced to stop.

Because you’ll be alternating fast and slow efforts frequently, low-traffic areas make the session far more practical.

Use Hilly Terrain to Your Advantage

Kenyan elite runners conduct fartlek sessions at altitude on hilly terrain. Using hills and elevation lets you raise exercise intensity without increasing pace — ideal when you cannot train at altitude but do have rolling terrain nearby.

High-altitude training is out of reach for most recreational runners, but if you have hills close by, use them actively.

Monitor Intensity with Heart Rate

Hilly terrain makes it impractical to stick to flat road paces. For runners accustomed to pace-based training, this raises the question: how do I measure effort?

The answer is heart rate. It is not a perfect proxy for exercise intensity, but it is the most practical quantitative tool recreational runners have for tracking effort in real time.

Accurate heart rate measurement requires either an optical wrist heart rate monitor or an electrical chest strap heart rate monitor. The article below covers recommended options.

Use RPE to Guide Your Effort

Fartlek’s core benefit is controlling intensity by feel, which lets you train with reserve. Research on trained runners found that self-paced intervals at durations of 1, 2, 4, and 6 minutes all produced a remarkably stable rate of perceived exertion (RPE) of around 17 — regardless of interval length ※4. Adjusting pace by feel consistently delivers a reliable training stimulus.

Use fartlek to sharpen your pace awareness: get a feel for how your perceived effort, heart rate, and pace connect across different intensity levels.

If your training has become stale or you want a session you can actually look forward to, give fartlek a try.

References

※1 Csepregi É et al. (2020) “The effects of breathing exercises in comparison with other exercise programs on cardiorespiratory fitness among healthy female college students” Journal of Sports Medicine and Physical Fitness

※2 Billat VL et al. (2000) “Intermittent runs at vVO2max enables subjects to remain at VO2max for a longer time than intense but submaximal runs” European Journal of Applied Physiology

※3 MacDougall JD et al. (1998) “Muscle performance and enzymatic adaptations to sprint interval training” Journal of Applied Physiology

※4 Seiler S, Sjursen JE (2004) “Effect of work duration on physiological and rating scale of perceived exertion responses during self-paced interval training” Scandinavian Journal of Medicine and Science in Sports