Why I’m Running 5Ks to Train for a Marathon (And You Should Too)
This morning I ran the Pleasanton Spirit Run 5K and crossed the line in 22:42. Even splits, steady effort, and a whole lot of mental grit. I haven’t been running that fast in training lately, but racing wakes up something different. I leaned on experience, pumping my arms, lifting through the mid-foot, steady self-talk when the fatigue rolled in. That honest effort told me exactly where my fitness is with CIM on the horizon; and what to do next.
The Short Race That Teaches Long Lessons
As runners get more experienced, we tend to chase longer distances. The marathon feels serious. The 5K can feel… casual. But if you’re actually giving it your all, the 5K is anything but casual. It’s controlled fire. And it’s powerful for marathoners because:
It sharpens cadence and leg turnover. Marathon pace can make your stride sleepy. A 5K wakes up your mechanics.
It builds competitive focus. Three miles of sustained discomfort is a safe place to practice grit you’ll need at mile 22.
It improves running economy. Short, fast reps raise the ceiling so marathon pace sits lower on the effort scale.
It checks your fitness now. A hard 5K gives you an honest snapshot of where to adjust training before CIM.
What a 5k Taught Me (and Might Teach You)
Today’s race confirmed two things:
The base is there. Even splits tell me aerobic strength is solid.
Speed and durability need a nudge. I’m adding one–two easy runs each week for endurance and one–two speed sessions for turnover.
If you’re eyeing CIM, that’s the recipe: keep the long run truly easy, keep easy days easy, and don’t skip speed. Smart beats more.
My Favorite 5K Workout for Marathoners
Keep it simple and consistent:
400m repeats at current 5K–10K pace
6–12 reps depending on how you feel that day
2–3 minutes recovery between reps (full recovery to keep quality high)
Focus on smooth mechanics: quick feet, relaxed jaw, elbows back, tall posture
This session lifts your stride without frying your legs—perfect inside a marathon build.
A 4-Week 5K Tune-Up Block for CIM Runners
Drop this on top of your existing base. The goal is to sharpen, not overhaul. Keep long runs easy ("Kenyan slow") and protect recovery days.
Intensity Key: Easy = conversational. Moderate = steady but controlled. Hard = 5K effort. RPE scale 1–10.
Week 1 – Wake the Legs
Mon: Easy 30–45 min + mobility (RPE 3–4)
Tue: Speed #1: 8 x 400m @ 5K pace, 2:00–2:30 walk/jog recovery (RPE 7–8)
Wed: Easy 40–50 min (RPE 3–4)
Thu: Strength Endurance: 4–5 miles progression: miles 3–4 at marathon pace (RPE 6)
Fri: Rest or 20–30 min easy + strides
Sat: Long run 13–15 miles easy, finish with 6 x 20s strides (RPE 3–4)
Sun: Off or cross-train (bike, swim, walk)
Week 2 – Build Consistency
Mon: Easy 30–45 min + light core
Tue: Speed #1: 10 x 400m @ 5K pace, 2:00 recovery (aim even splits)
Wed: Easy 45–50 min
Thu: Fartlek: 10 x 1:00 hard / 2:00 easy (hard = 5K effort)
Fri: Rest or 25–35 min easy
Sat: Long run 14–16 miles easy, last 2 miles steady (RPE 4–5)
Sun: Off or mobility
Week 3 – Sharpen, Don’t Smash
Mon: Easy 30–40 min + drills (A/B skips, high knees)
Tue: Speed #1: 6 x 600m @ between 5K and 10K pace, 2:30–3:00 recovery
Wed: Easy 45–50 min
Thu: Tempo Taste: 4–5 miles continuous at half-marathon effort (RPE 6–7)
Fri: Rest or 20–30 min easy + 6 x 15s strides
Sat: Long run 15–18 miles easy (RPE 3–4)
Sun: Off
Week 4 – Race Week (Tune-Up 5K)
Mon: Easy 30 min + mobility
Tue: Primer: 6 x 200m @ 3K–5K pace, full walk-back recovery
Wed: Easy 25–35 min
Thu: 5K Time Trial / Race – Warm up 10–15 min easy + drills + 4 x 20s strides. Start controlled, finish brave.
Fri: Off or 20–30 min recovery jog
Sat: Easy 40–50 min
Sun: Long run 16–20 miles easy (keep it gentle)
Notes for Masters and High-Mileage Runners
Masters (40+): keep recoveries generous; consider capping at 8–10 reps.
High mileage: fold Tue/Thu quality into existing mileage; never stack hard days back-to-back.
How to Pace the 5K So It Helps Your Marathon
Even > heroic. Start at goal pace, not faster. Today’s 22:42 worked because I resisted the surge.
Breathe tall, elbows back. Form cues beat watch-staring when it gets hard.
Compete the last mile. That’s where you practice marathon-mile-22 focus.
Train Smarter for CIM (Not Just More)
My own best CIM came from a simple template: one speed session, one long run, and social easy miles. Not fancy—just consistent and honest. If you want a plan that fits your life, protects your body, and still chases that PR or BQ, I’d love to help.
CIM Coaching with Running Fit Lab
Customized weekly plans (built around your work/family schedule)
Feedback on workouts and race strategy (including tune-up 5Ks)
Strength, mobility, and mental skills that show up on race day
👉 Spots are open for November starts. Ready to get faster for CIM? Let’s train together.