Want to Run a Sub-20 5k

This next fall will be my last season of high school cross-country. I’ve been on Varsity the past two years, but this past season my PR fell from a 20:11 to a 20:30. I was very upset but am now determined to break 20 minutes next season. After my track season I’ll take a break and then have about 13 weeks to prepare. I want to get faster but not get injured. Any suggestions?

— Jamie Chandler, Alpharetta, GA, USA

Answer by Dom:

Hey Jamie — thanks for writing in. First, I’d like you to know that a slip from 20:11 to 20:30 is not the disaster it feels like right now. These things happen, usually when a runner has been racing hard without enough aerobic base underneath them. The good news is that you have 13 weeks, a clear goal, and the right attitude. I’m confident that with sensible preparation you can break that 20-minute barrier in your final season.

A sub-20 5k means running each kilometre in 3:59 or each mile in 6:25. That is your target. Every decision you make in training should serve that number.

Here is what I’d like you to work through:

1. Value the different types of running workouts
2. Building or increasing your base
3. A 13-week framework
4. The importance of goal pace workouts
5. The race week taper

Value the Different Types of Running Workouts

A strong 5k training plan draws on several different types of running, and understanding what each one does will help you train with purpose rather than just putting in miles.

• Easy runs — conversational-pace running that builds your aerobic engine and keeps you fresh between harder efforts. The majority of your running should be here.
• Tempo runs — steady, comfortably hard efforts that raise your lactate threshold, so you can sustain a faster pace before things start to hurt.
• Interval runs — shorter, high-intensity repetitions with recovery periods in between. These sharpen your speed and boost cardiovascular capacity.
• Long runs — your longest run of the week, done at an easy pace. Long runs build stamina and make you a stronger runner across every distance.
• Strides — short, relaxed accelerations tacked on to the end of easy runs. They keep speed in your legs without adding any real fatigue.

All of these belong in your programme. But here is the part most young runners get wrong: the overwhelming majority of your running—I’d say 80% or more—should be genuinely easy. For you, Jamie, that means around 8:00–8:15 per mile for easy runs and 8:30–9:00 per mile for your long run. That feels slow. It should feel slow. Trust it.

I don’t know exactly how your coach structures your programme, but if you have any influence over it, push for more easy miles. More easy running is rarely the wrong answer at your stage of development.

Building or Increasing Your Base

My strong suspicion about your PR slipping from 20:11 to 20:30 is that your aerobic base was not quite where it needed to be. Too much racing intensity without enough easy mileage underneath it tends to produce exactly that result. The fix is straightforward, if not always exciting: build your base properly this time.

When you establish a stronger base, you are giving your body the capacity to run faster for longer without wearing out. A proven way to do this is through steady, gradual mileage increases over a sustained period. Think of your training plan as a ladder—you only step up to the next rung when you are comfortable where you are. Patience is not optional here; it is the whole point.

I am often struck by how much progress comes from simply running more easy miles. Suddenly holding goal pace feels a little less brutal—not because you have done more hard work, but because you have built more aerobic endurance and your body has learned to run efficiently. That is base building doing its job.

Increase your weekly mileage by no more than 10% from one week to the next. Listen to your body. If you feel a niggle, back off. A week of reduced mileage now is worth far more than a month on the sidelines. Have a look at the base building page for more detail on how to structure this phase.

A 13-Week Framework

Thirteen weeks is a genuinely useful block of time—enough to build real fitness, add quality work, and arrive at your race sharp and confident. Here is how I’d like you to think about it.

Phase 1 — Base (weeks 1–5)

Easy running only. No hard efforts at all during this phase. Build your weekly mileage from your current level up toward 30–35 miles per week. Your long run should grow from around 6–7 miles in week one to 9–10 miles by the end of week five. Add 6–8 strides at the end of two or three easy runs per week—these keep your legs feeling lively without stressing your body. This phase is unglamorous. Do it anyway.

Phase 2 — Quality (weeks 6–10)

Keep easy running as the foundation. Now add one tempo session per week: start at 20 minutes of continuous running at threshold effort (roughly 7:10 per mile for you, Jamie—about 45 seconds per mile slower than your goal race pace) and build to 30–35 minutes by week ten. Add one interval session per week: 6 × 800m or 5 × 1000m at 5k effort. Your easy runs and long run continue unchanged.

Phase 3 — Race-Specific (weeks 11–13)

This is where you sharpen up. Swap longer tempo efforts for shorter, faster work. Introduce goal pace repetitions: 12 × 400m at 1:35–1:36 per rep. Reduce your overall mileage by 20–25% in week twelve as you move toward the taper. Week thirteen is covered below.

The Importance of Goal Pace Workouts

You need to know what sub-20 pace feels like in your legs—not just in your head. That is exactly what goal pace workouts are for. Running 12 × 400m at 1:35–1:36 per rep trains your body and your mind to recognise 6:25-per-mile effort and hold it non-stop under fatigue.

I’d start these in phase three once your base and quality work are in place. Running goal pace too early, on tired legs or without adequate mileage underneath you, tends to produce either poor sessions or niggles. Earn the right to run fast by doing the base work first.

Have a look at the goal pace page for more detail on how to structure these sessions and how to progress them as your race approaches.

By combining a wide range of workouts, building your base progressively, and bringing in goal-pace work at the right moment, you have everything you need to cross that finish line in under 20 minutes.

The Race Week Taper

The final week before your race is not the time to squeeze in extra work. Reduce your total volume by 30–40% compared to a typical training week. Keep two short quality sessions — something like 4 × 200m at goal pace, or a 10-minute tempo effort — to stay sharp without adding fatigue. Everything else is easy running.

Sleep well. Do not try anything new with your kit, your food, or your warm-up routine. Trust the fitness you have built over thirteen weeks. The biggest mistake runners make in taper week is feeling good and adding extra sessions to use up that energy. Resist it. That feeling of freshness is exactly what you want to carry to the start line.

A final thought: especially when you are staring down one big goal — enjoy the process. :) Keep your running consistent. Build your mileage. Become a better runner over the full thirteen weeks. And let that sub-20 be the result of that work, rather than something you chase with your eyes fixed solely on the clock.

Best of luck and best wishes,

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