When to Add Fartlek Surges to Your Easy Run

Fartlek is a Swedish word meaning "speed play." As a standalone workout, it involves alternating between faster surges and easy jogging for 30 to 50 minutes. But fartlek also works as a modifier: instead of a dedicated session, you scatter a handful of short surges through an otherwise easy run.

This is a gentler introduction to intensity than a tempo run or threshold session. The surges are brief, the recovery is as long as you want, and the overall character of the run stays easy. It is particularly useful during the base phase, when structured threshold work has not yet begun but you want to give the body a taste of faster running.

What It Looks Like

You head out for a normal easy run. After 10 to 15 minutes of warming up, you pick up the pace for 30 to 90 seconds, then return to easy pace for 2 to 4 minutes. Repeat 4 to 6 times. Finish the run easy.

The surges are run by feel, not by pace or heart rate. Some will be moderate. Some will approach threshold effort. That variability is the point. You are not trying to hit a target; you are practicing the ability to change speeds and settle back into rhythm.

There is no formal structure. You can surge when you feel like it, use landmarks (lamppost to lamppost, one lap of the park), or set loose time intervals. The absence of rigid structure is what separates fartlek surges from interval training.

Why It Works

Bridging aerobic and threshold training

During the base phase, most running is easy. Jumping straight from 100% easy running to structured tempo work is a sharp transition. Fartlek surges provide an intermediate step. They expose the body to efforts above easy pace without the sustained stress of threshold work. This prepares muscles, tendons, and the cardiovascular system for the harder training coming in the build phase.

Developing pace variability

In a marathon, you will not run every kilometre at the same pace. Hills, wind, crowds, aid stations, and mental fluctuations all create pace variation. Fartlek surges train your body and brain to accelerate, hold a faster pace briefly, and then return to a sustainable effort without panicking. This gear-shifting ability is undervalued in marathon preparation.

Low-risk intensity

The surges are short and the recovery is complete. The overall training load of an easy run with 5 to 6 fartlek surges is only marginally higher than a plain easy run. This makes fartlek surges one of the safest ways to introduce faster running, especially for runners returning from injury or coming off a break.

Keeping training interesting

An honest benefit. Weeks of purely easy running during the base phase can become monotonous. Scattering a few surges into an easy run adds variety and engagement without changing the fundamental character of the session.

Which Runs to Add Them To

Easy runs (the natural pairing)

A 40 to 55 minute easy run with 4 to 6 surges is the standard combination. The surges add maybe 3 to 6 minutes of faster running across the whole session. The run remains predominantly easy.

Best on a day when you have good energy and no residual fatigue from a previous hard session. Avoid adding surges on a day when you are tired. If the easy pace already feels like work, it is not the right day for fartlek.

Long runs (very rarely)

A few light surges in the middle of a long run can work during the base phase before long runs start including marathon-pace segments. But this combination is unusual and generally not necessary. Once long runs begin including structured quality (MP segments, progression finishes), fartlek surges become redundant.

Recovery runs (never)

Same principle as strides and progression finishes: recovery runs are recovery. Adding surges, even gentle ones, introduces training stress.

When in the Training Cycle

Base phase (primary use): Fartlek surges are most valuable during the base phase, when they serve as the earliest introduction to faster running. One to two easy runs per week with fartlek surges is sufficient. This bridges the gap between pure aerobic running and the structured threshold work that begins in the build phase.

Build phase (decreasing): As dedicated threshold sessions (tempo runs, threshold intervals, marathon pace work) enter the program, fartlek surges become less necessary. The body is getting faster-running stimulus from the quality sessions. One session per week with fartlek surges can still add variety, but it is no longer a primary intensity source.

Peak phase (occasional): Used sparingly as an alternative to structured quality on a lighter week. Some coaches prescribe easy runs with surges during reduced-load weeks within the peak phase to maintain intensity at a lower overall cost.

Taper phase (rarely): Light surges in the final weeks before a race are generally unnecessary. Strides serve the neuromuscular purpose more efficiently, and short threshold touches handle the pacing-maintenance role.

Fartlek Surges vs. Strides

These two modifiers are easy to confuse. The differences matter:

Strides are about neuromuscular precision: short, fast, fully recovered. Fartlek surges are about sustained-effort variability: longer, less intense, embedded within the run. Both can appear in the same training week, but they should not appear in the same run. One modifier per session.

Common Mistakes

Making the surges too hard. Fartlek surges are supposed to be speed play, not speed work. If you finish the run feeling drained, the surges were too intense or too long. The overall run should still feel like an easy day with some spice.

Making the surges too structured. Prescribed reps and rest intervals turn fartlek into interval training. The whole point of fartlek is that it is flexible and intuitive. Surge when you feel like it, for as long as it feels good.

Not recovering between surges. If you string surges together with only 30 seconds of easy running between them, you are doing a continuous tempo effort in disguise. Give yourself at least 2 minutes of easy running between surges to return to a relaxed state.

Using fartlek surges when threshold work is available. During the build and peak phases, threshold sessions provide a more targeted and measurable stimulus. Fartlek surges are a bridge, not a replacement. If you have a tempo run on the schedule, don't skip it in favour of "I'll just do fartlek instead."

Practical Guidelines

• Number of surges: 4 to 6 per session
• Surge duration: 30 to 90 seconds each
• Surge intensity: Moderate to comfortably hard (RPE 6 to 7). Not all-out.
• Recovery between surges: 2 to 4 minutes at easy pace
• When in the run: After a 10 to 15 minute easy warmup, scattered through the middle, stop surges 5 to 10 minutes before finishing
• Frequency: 1 to 2 times per week during base phase; decreasing in build and peak
• Don't combine with strides. One modifier per run.