You’ve been running three times a week for six months and your 5K time hasn’t budged. Every run feels the same pace, the same effort, the same result. Sound familiar? The fix isn’t running more — it’s running differently. Interval training is how you break through a plateau, and once you understand the mechanics, you’ll wonder why you spent so long plodding along at the same speed.
In This Article
- What Interval Training Actually Is
- Why Intervals Make You Faster
- Types of Interval Sessions
- Five Interval Sessions to Try
- How to Structure an Interval Session
- Pacing Your Intervals
- How Often Should You Do Intervals
- Where to Run Intervals
- Common Interval Training Mistakes
- Interval Training for Different Goals
- Recovery Between and After Sessions
- Frequently Asked Questions
What Interval Training Actually Is
Interval training alternates between periods of hard effort and periods of recovery. Run fast for a set time or distance, slow down or stop to recover, then go fast again. That’s it — the concept is simple even if the execution makes your lungs burn.
The Basic Structure
Every interval session has the same building blocks:
- Work interval — the fast bit. Could be 30 seconds or 5 minutes depending on the session type
- Recovery interval — the slow bit. Walking, jogging, or standing still. Long enough to partially recover, short enough to keep the training stimulus going
- Repetitions — how many work intervals you do in one session
- Sets — groups of repetitions with longer rest between sets
How It Differs From Tempo Running
Tempo runs are sustained efforts at a “comfortably hard” pace for 20-40 minutes. Intervals are shorter, harder efforts with rest between them. Both improve speed, but through different mechanisms — tempo builds lactate threshold endurance, intervals build VO2 max and raw speed.
Why Intervals Make You Faster
VO2 Max Improvement
Your VO2 max is the maximum amount of oxygen your body can use during exercise. It’s one of the strongest predictors of running performance. Interval training pushes your cardiovascular system to its limit repeatedly, forcing adaptations that increase your VO2 max over weeks and months. The NHS recommends vigorous activity like interval training as part of a balanced fitness routine.
Running Economy
Running economy is how efficiently you use oxygen at a given pace. Intervals teach your body to recruit muscle fibres more efficiently, improve your biomechanics at speed, and make your target race pace feel easier. After eight weeks of consistent interval training, I shaved 45 seconds off my 5K — not from running more miles, but from running smarter ones.
Lactate Threshold
During hard running, your muscles produce lactate faster than your body can clear it. The point where lactate accumulates is your lactate threshold — and that burning sensation in your legs is the result. Intervals train your body to clear lactate more efficiently, pushing the threshold higher so you can sustain faster paces before the burn kicks in.
Mental Toughness
There’s no polite way to say this — intervals hurt. The last rep of a set of 800m repeats at 5K pace is deeply unpleasant. But doing it week after week teaches you to run through discomfort, and that mental skill transfers directly to races. The final kilometre of a 10K feels more manageable when you’ve practiced pushing through fatigue in training.
Types of Interval Sessions
Short Intervals (100m-400m)
- Pace: Faster than your 5K race pace — close to a sprint
- Recovery: Walk or very easy jog, typically 60-90 seconds
- Purpose: Develops raw speed, running form at pace, and fast-twitch muscle fibre recruitment
- Example: 10 × 200m with 90 seconds jog recovery
Medium Intervals (600m-1,200m)
- Pace: At or slightly faster than your 5K race pace
- Recovery: Jog recovery for 2-3 minutes (or half the work interval time)
- Purpose: Builds VO2 max — the core of most interval training programmes
- Example: 6 × 800m at 5K pace with 2 minutes jog recovery
Long Intervals (1,600m-2,000m)
- Pace: Between your 5K and 10K race pace
- Recovery: 3-4 minutes jog recovery
- Purpose: Builds speed endurance — the ability to hold a fast pace for longer
- Example: 4 × 1,600m at 10K pace with 3 minutes recovery
Hill Intervals
- Pace: Hard effort uphill (don’t focus on speed — the hill provides resistance)
- Recovery: Jog back down the hill
- Purpose: Builds strength, power, and running-specific muscle endurance without the joint impact of flat sprinting
- Example: 8 × 60-second hill repeats with jog-down recovery
Fartlek
Swedish for “speed play” — an unstructured session where you vary your pace based on feel, landmarks, or time. Sprint to the next lamppost, jog to the bus stop, run hard up the hill, easy on the flat.
- Purpose: Introduces speed work in a low-pressure, flexible way. Perfect for beginners or as a lighter alternative to structured intervals
- Example: 40 minutes of easy running with 6-8 hard efforts of 30-90 seconds scattered throughout
Five Interval Sessions to Try
Session 1: The Beginner (Fartlek)
For runners new to speed work.
- Warm up with 10 minutes easy jogging
- Run hard for 30 seconds (not a sprint — think “fast but controlled”)
- Jog easy for 90 seconds
- Repeat 8 times
- Cool down with 10 minutes easy jogging
Total time: About 35 minutes. This introduces your body to pace changes without the pressure of hitting specific times.
Session 2: The 5K Sharpener (800m Repeats)
The classic speed session for 5K improvement.
- Warm up with 10-15 minutes easy jogging plus 4 strides
- Run 800m at your current 5K race pace
- Jog easy for 2 minutes
- Repeat 5-6 times
- Cool down with 10 minutes easy jogging
Total time: About 45 minutes. If you don’t know your 5K pace, run each 800m at the fastest pace you could sustain for 25 minutes.
Session 3: The Speed Builder (200m Sprints)
For developing raw leg speed.
- Warm up with 15 minutes easy jogging plus 4 strides
- Sprint 200m at close to maximum effort
- Walk or very easy jog for 90 seconds
- Repeat 10 times
- Cool down with 10 minutes easy jogging
Total time: About 40 minutes. These are genuinely hard — expect to feel your form breaking down on the last 2-3 reps. That’s normal.
Session 4: The Hill Session
For strength and power.
- Find a hill that takes 45-60 seconds to run up at hard effort (about 6-8% gradient)
- Warm up with 10 minutes easy jogging on the flat
- Run hard up the hill — drive your arms, lean slightly forward, short quick steps
- Jog easy back down
- Repeat 8-10 times
- Cool down with 10 minutes easy jogging
Total time: About 40 minutes. Hill running is lower-impact than flat sprints because the gradient reduces the braking force on each stride.
Session 5: The 10K Prep (1,600m Repeats)
For building speed endurance.
- Warm up with 15 minutes easy jogging plus 4 strides
- Run 1,600m (4 laps of a track or 1 mile) at your 10K race pace
- Jog easy for 3 minutes
- Repeat 3-4 times
- Cool down with 10 minutes easy jogging
Total time: About 50 minutes. The longer intervals build the endurance component of speed — holding a fast pace when tired.
How to Structure an Interval Session
Warm-Up (Non-Negotiable)
Every interval session needs at least 10 minutes of easy jogging followed by 4-6 strides (short accelerations of 15-20 seconds, building to about 90% effort). This raises your heart rate gradually, loosens muscles, and primes your nervous system for fast running. Skipping warm-up is the fastest route to a hamstring injury.
The Main Set
The intervals themselves. Start conservatively — the first rep should feel manageable. If you go out too hard on rep 1, you’ll crawl through reps 4, 5, and 6. Even pacing across all reps is the goal.
Cool-Down
At least 10 minutes of easy jogging. This helps clear lactate from your muscles and begins the recovery process. Walking is fine if you can’t jog after a hard session.
Pacing Your Intervals
By Feel
If you don’t have a GPS watch, pace by perceived effort. Your hard intervals should feel “uncomfortable but sustainable” — you shouldn’t be able to hold a conversation, but you also shouldn’t feel like you’re about to collapse.
By Time (GPS Watch)
If you have a GPS watch, use your recent race times to calculate interval paces. Our GPS watch guide for interval training explains how to set up interval mode and programme rest periods.
The Talk Test
- Easy recovery: Can chat comfortably
- Interval pace: Can manage a few words between breaths
- Too fast: Can’t speak at all — back off slightly
Don’t Chase Every Rep
Some reps will feel better than others. If rep 3 feels sluggish, don’t force it faster — run to effort level, not to the clock. Consistency across the session matters more than one blazing rep followed by three slow ones.
How Often Should You Do Intervals
For Most Recreational Runners
Once per week is enough. Two quality sessions (one interval, one tempo or long run) plus 2-3 easy runs makes a solid training week for anyone targeting 5K to half marathon.
For Competitive Runners
Two interval sessions per week maximum, with at least 48 hours between them. The sessions should differ — one short and fast (200-400m), one longer (800-1,600m). More than two risks overtraining and injury.
Building Up
If you’ve never done intervals, start with one fartlek session per week for 3-4 weeks. Then progress to structured intervals. Jump straight into 10 × 800m without a build-up phase and your calves will have words with you.
When to Rest
If you’re feeling flat, your resting heart rate is elevated, or your easy runs feel harder than usual, skip the interval session and run easy instead. One missed session does nothing. Two weeks of forced training on tired legs leads to injury.
Where to Run Intervals
Running Track
The ideal venue. Exact distances, flat surface, no traffic, no puddles. Most UK athletics tracks offer pay-as-you-go sessions for about £3-5. Check your local council leisure centre or athletics club.
Measured Road or Path
Use your GPS watch or map a route in advance. Canal towpaths, park perimeters, and promenades work well — flat, uninterrupted, and safe.
The Treadmill
Perfectly valid for intervals. Set the speed for your work interval, hit the belt buttons for recovery. The treadmill removes pacing guesswork entirely. Some people find it mentally harder — staring at a wall for 6 × 800m is less inspiring than running in the park.
Parkland
Fartlek sessions work brilliantly in parks. Use landmarks — sprint to the oak tree, jog to the bench, hard to the hill crest. The varied terrain adds a natural strength element. If you’re building up from beginner level, our Couch to 5K guide covers the foundation work before you start speed sessions.
Common Interval Training Mistakes
- Going too hard on the first rep — if rep 1 is your fastest, you started too fast. Aim for even splits across all reps
- Not recovering enough between reps — the recovery interval isn’t wasted time. It’s where your body clears lactate and prepares for the next effort. Cutting recoveries short degrades the quality of subsequent reps
- Doing intervals every run — easy runs are where your body adapts to the hard work. Skip them and you’re just accumulating fatigue without building fitness
- Ignoring the warm-up — cold muscles don’t produce force efficiently and tear more easily. 10 minutes of easy jogging is non-negotiable before any speed work
- Running intervals on tired legs — if yesterday was a hard run, today should be easy. Intervals on fatigued legs teach your body to run badly at speed — the opposite of what you want
- Comparing yourself to faster runners — your interval pace is based on YOUR current fitness. Running someone else’s paces leads to burnout, injury, or both
Interval Training for Different Goals
5K Improvement
Focus on 400m-800m intervals at your current 5K pace or slightly faster. One session per week for 8 weeks typically produces a 30-60 second improvement.
10K Improvement
Mix 800m-1,600m intervals at 10K pace with shorter 400m reps at 5K pace. The longer intervals build specific endurance; the shorter ones maintain top-end speed.
Half Marathon
Long intervals (1,600m-2,000m) at half marathon pace plus medium intervals (800m-1,200m) at 10K pace. One interval session per week alongside one tempo run and a weekly long run.
General Fitness
Fartlek once or twice a week. No timing, no pressure. Just vary your pace throughout a normal run to build cardiovascular fitness and prevent boredom.
Recovery Between and After Sessions
Between Reps
Jog slowly — don’t stop completely unless you’re doing very short sprints (100-200m). Jogging keeps blood flowing and helps clear lactate faster than standing still.
After the Session
- Cool down with 10+ minutes of easy jogging
- Stretch the major muscle groups — calves, hamstrings, quads, hip flexors
- Refuel within 30 minutes — a mix of protein and carbohydrates helps muscle repair. Even a banana and a glass of milk is enough
- Hydrate — drink to thirst. You don’t need a sports drink for a 45-minute session unless it’s hot
Between Sessions
Leave at least 48 hours between interval sessions. Fill the days between with easy running (conversational pace), rest days, or cross-training. Your body adapts during recovery, not during the hard session itself.
Frequently Asked Questions
Can beginners do interval training? Yes, but build a base first. Run consistently for 6-8 weeks (3 runs per week at easy pace) before introducing speed work. Start with fartlek — unstructured speed play — before progressing to timed intervals.
How long before I see results from intervals? Most runners notice improvements within 4-6 weeks of consistent weekly intervals. The first gains are often mental — race pace feels more manageable — followed by measurable time improvements at 6-8 weeks.
Should I eat before an interval session? A light snack 60-90 minutes beforehand works for most people — a banana, toast with peanut butter, or a small energy bar. Running hard on a full stomach causes nausea. Running completely empty can leave you flat. Experiment in training, not on race day.
Are intervals better than long slow runs? They’re complementary, not competing. Long runs build aerobic endurance and fat-burning efficiency. Intervals build speed, VO2 max, and lactate clearance. A good training plan includes both. Dropping all easy running in favour of intervals leads to burnout and injury.
Can I do intervals on a treadmill? Yes — treadmills work well for intervals because you can set exact speeds and rest periods. The slight cushioning also reduces impact. The downside is boredom and the lack of wind resistance. Set the incline to 1% to approximate outdoor effort.