Owen PalmerBy Owen Palmer

Updated November 2026

The main disadvantages of fartlek training, as BBC Bitesize describes the method, are that it is unstructured, hard to measure, and can lead to too much hard running for some athletes. Because pace and effort are chosen on the fly, runners may drift into workouts that are too easy or too hard, which makes progress harder to track and recovery harder to plan.

Fartlek, a Swedish term meaning “speed play,” is a useful tool, but it is not a perfect fit for every runner or every goal. Understanding its limits helps you decide when to use it and when to choose something more controlled.

Shopping for one? See our guide: Disadvantages of Fartlek Training (2026): When It Isn't the Right Choice.

Why Fartlek Can Be Hard to Control

The core appeal of fartlek is its freedom. You run faster for a while, then recover, with no fixed distances or times. That same freedom is the source of its main weakness. Without clear targets, many runners speed up too much on the “fast” segments and never fully recover on the “easy” ones. Over several sessions, this can turn a planned moderate workout into a string of hard efforts.

Beginners are especially prone to this. They often treat every surge as a race and finish the session more tired than intended. The workout may feel productive, but it can interfere with the easy runs and long runs that build aerobic base.

The Factors Behind the Drawbacks

Several factors make the disadvantages more noticeable:

  • Lack of measurement. Fartlek rarely specifies exact paces, so it is difficult to compare one session to the next or show improvement over time.
  • Subjective effort. Judging “hard” and “easy” by feel varies with sleep, nutrition, stress, and terrain. Two identical-looking sessions can produce very different training loads.
  • Limited progression. It is hard to apply clear overload principles when the workout has no defined structure to make harder over the weeks.
  • Terrain and surface. Hills, trails, and uneven ground change the effort required for the same time, which can skew how hard the session really is.
  • Poor fit for race-specific goals. If you are preparing for a 5K or 10K with a target pace, the loose nature of fartlek may not train the exact speed you need.

Fartlek also places less emphasis on the precise recovery intervals found in track or structured interval work, so the body may not be pushed to a defined stimulus at race pace.

What to Do About It

You do not have to abandon fartlek. You can keep its spirit while reducing its weaknesses. The goal is to add just enough structure to make the session measurable and safe.

  1. Set rough targets. Choose a range, such as “hard but controlled” for 30 to 60 seconds, rather than sprinting every time.
  2. Use a timer or watch. Time your fast and easy segments so you can repeat the pattern and compare sessions.
  3. Cap the hard portion. Keep fast segments under a set share of total running time, often about 20 to 30 percent for most recreational runners.
  4. Pick flat or consistent routes. Consistent terrain makes effort easier to judge.
  5. Keep easy days easy. Make sure the recovery portions are genuinely slow, and do not stack fartlek on consecutive hard days.
  6. Log each session. Note segment lengths, perceived effort, and how you felt the next day to spot patterns.
  7. Switch to structured intervals when needed. For race-specific preparation, use defined repeats with set paces.

If you have a medical condition, are returning from injury, or feel unusual symptoms during hard running, consult a doctor or qualified coach before increasing intensity.

Is fartlek training good for beginners?

It can be, as long as beginners keep the fast segments controlled and the easy segments truly easy. Starting with short surges is a sensible approach.

How often should I do fartlek?

Many runners include one fartlek session per week alongside easy runs and a long run. Spacing hard sessions apart helps recovery.

Can fartlek replace interval training?

It can supplement interval work, but it is usually less precise. For a specific race pace, structured intervals are typically more effective.

How do I know if a fartlek session is too hard?

If you cannot hold a conversation during the fast segments, or if you feel exhausted for two or more days afterward, the session was likely too intense.

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Owen Palmer

About Owen Palmer

Owen Palmer is part of our editorial team and reviews and edits our speed & interval running guides, checking product details against manufacturer specifications and owner feedback.