Road Running Speed Training: Differences and Applications of Tempo Run vs Intervals vs Fartlek

Introduction

“Today I want to work on speed—should I do intervals?” Many runners equate “speed training” with “interval training,” but in reality, road running speed training encompasses three distinctly different methods: Tempo Run, Interval Training, and Fartlek. Each has its own physiological goals, suitable contexts, and placement within a training cycle. Use them correctly and you’ll get twice the results with half the effort; use them incorrectly and you may waste your energy or even increase your risk of injury.

Comparison of the Three Speed Training Methods

Tempo Run

Definition and Mechanism

Tempo Run, also known as Lactate Threshold Run, is running continuously at a “comfortably hard” intensity. This intensity corresponds to the lactate threshold (LT)—the critical point at which lactate begins to accumulate rapidly.

Running continuously at lactate threshold intensity stimulates the body’s ability to clear lactate at high intensities and pushes up the pace corresponding to the lactate threshold. In other words, Tempo Run allows you to sustain an aerobic state at faster speeds, which directly affects your race pace ceiling for half marathons and full marathons.

Pace Calculation

• Heart rate method: 82–87% of maximum heart rate (using a common maximum heart rate of 180bpm in Taiwan as an example, approximately 147–157bpm)
• Talk test: Can speak 3–5 words, but cannot hold a comfortable conversation
• Pace reference: Typically 20–40 seconds/km slower than 5K pace, and 10–20 seconds/km faster than half marathon pace

Workout Examples

• Continuous Tempo: 2km warm-up + 25 minutes Tempo + 2km cool-down (most common format)
• Segmented Tempo: 2km warm-up + 15 minutes Tempo + 3 minutes rest + 15 minutes Tempo + 2km cool-down
• Tempo Long Run: Insert 20–30 minutes of Tempo intensity into the middle of a long run

Interval Training

Definition and Mechanism

Interval training involves short bursts at intensities above the lactate threshold (VO2max zone), followed by structured rest, then repeated. The goal of interval training is to stimulate improvements in VO2max, the most critical indicator determining your aerobic capacity ceiling.

The way to improve VO2max is to keep your heart rate at 90–95% or more of maximum for a sustained period (typically 2–5 minutes per rep), and the structured rep-and-rest format of interval training is the most effective way to achieve this.

Workout Examples

• 800m×6: 5×800m with 2 minutes of jogging between reps, at 5K goal pace
• 1000m×5: 5×1000m with 90 seconds rest between reps, slightly slower than 5K pace
• Short Intervals: 10×400m with 400m jog between reps, at 5K pace or faster

When Is Interval Training Most Appropriate?

• From the build phase to the peak phase: Not suitable for heavy use during the base phase; you need an aerobic foundation to fully benefit
• 8–12 weeks before race day: Allows VO2max improvements to translate into race performance
• At most 1–2 times per week: Intervals require full recovery; frequency should not be too high

Fartlek

Definition and Mechanism

Fartlek originates from Swedish, meaning “Speed Play.” It is an unstructured form of speed training—within a continuous run, you naturally accelerate and decelerate based on feel or terrain, with no fixed distances or times.

Unlike Tempo Run and intervals, Fartlek’s intensity fluctuates, ranging from easy running to near-sprinting. This multi-intensity stimulus trains the body to switch quickly between different paces while keeping the mind fresh.

Workout Examples

• Time-based Fartlek: During a 30-minute easy run, add 8 alternating rounds of “2 minutes fast, 2 minutes recovery”
• Landmark-based Fartlek: Along your running route, accelerate to the next utility pole every time you see one, then resume easy running
• Number-based Fartlek (beginner-friendly): 1 minute fast, 1 minute slow × 10 rounds

Fartlek’s Unique Value

• Mental resilience training: Learn to keep running through discomfort without relying on a watch or pace
• A gentler entry into speed training: For runners new to speed work, Fartlek is more approachable than formal intervals
• Maintaining speed sensation between seasons: During the base or transition phase, use Fartlek occasionally to keep your speed feel

Placement of the Three Within a Training Cycle

• Base phase: Occasionally substitute Fartlek for easy runs to lightly maintain speed sensation; no formal intervals
• Early build phase: Begin introducing Tempo Run (once per week) + occasional Fartlek
• Mid-to-late build phase: Alternate Tempo Run and intervals (once each per week, but avoid two consecutive high-intensity days)
• Peak phase: Reduce interval frequency and increase the share of race pace runs
• 2 weeks before race day: Stop intervals; keep only short strides and light Fartlek to maintain the feel

Practical Advice

• Don’t turn a Tempo into intervals: Many runners start their Tempo Run too fast and blow up after 2km—a proper Tempo should be sustainable steadily throughout
• Intervals require a proper warm-up: At least 2km of easy running plus dynamic stretching, otherwise the injury risk is high
• Fartlek is great for off-schedule days: When your plan gets disrupted and you don’t have time for a formal workout, Fartlek is a flexible alternative
• Track how each workout feels: Record the pace, heart rate, and sense of completion for every speed session to help gauge your body’s condition

Conclusion

Tempo Run, intervals, and Fartlek are three different tools for road running speed training. Lactate threshold is improved through Tempo, VO2max is broken through with intervals, and speed flexibility is cultivated through Fartlek. Use the three in combination and bring them out at the right point in your training cycle to maximize the benefits of your speed work. The next time you plan a speed session, first ask yourself: “What is my goal today?”—the answer will tell you which tool to choose.

Related Reading

• Fartlek Workouts: The Freedom Training Method That Plays with Speed
• Speed Sessions for Marathon Training: Weekly Workout Planning for Intervals, Tempo, and Threshold Runs
• Designing Road Running Interval Workouts: Periodizing 400m, 800m, and 1600m Intervals
• Weekly Speed Training Plans for Road Running: Allocating Intervals, Tempo, and Easy Runs