Balanced Approach: Why Marathon Runners Need Both Strength Training and Cardio
- Kim Miller
- Sep 21
- 4 min read
Why female marathoners must combine strength training and cardio: the proven blueprint to improve running economy, prevent injury, and finish stronger.
The Debate That’s Holding Runners Back
"Running will build your endurance, but strength will keep you in the game. If you want to finish strong, you need both."
— Coach Kim, Founder of KimFit
If you’ve spent any time in a running group or scrolling fitness forums, you’ve heard it:
👉 “If you want to run a marathon, just run.”
👉 “Strength training makes runners bulky.”
👉 “Cardio burns fat, lifting just makes you sore.”
It’s the same tired debate—strength training vs. cardio.
But here’s the reality: cardio alone leaves you fragile. Strength alone leaves you unprepared. And if you’re a female marathoner chasing performance, longevity, and that finish-line photo where you actually look as strong as you feel, you need both.
At Kim Miller Fitness, we’ve trained tens of thousands of women through the KimFit App. From first-time marathoners to Boston qualifiers, one thing is consistent: the athletes who balance cardio and strength are the ones who run faster, stay healthier, and actually enjoy the sport long-term.
Emma’s Story: From Injured to Unstoppable
Emma, a 38-year-old mom of two, trained for her marathons the way most runners do—by piling on miles. She ran 50–60 per week, convinced that “more miles = better fitness.”
But every cycle ended the same way: hip pain, fatigue, missed workouts, and disappointment on race day. She finished, but she finished broken.
When she joined KimFit, we adjusted her training: slightly fewer junk miles, and just two strength sessions per week. Glutes, hamstrings, core, and upper body stability.
Within weeks, she noticed the difference:
Her stride felt smoother.
Long runs no longer left her wrecked.
She leaned out, got stronger, and recovered faster.
This time? Emma ran pain-free and PR’d by 12 minutes.
Her words after crossing the finish line?
“I felt SO STRONG!”
Emma isn’t the exception—she’s the example of what happens when the engine and the armor finally work together.
Cardio: Building the Engine
Cardio is non-negotiable. It’s your engine, and it delivers:
Aerobic capacity (VO₂ max):
your body’s ability to use oxygen efficiently.
Stamina:
the power to keep going for hours.
Heart and lung health:
endurance that fuels life beyond running.
Mental grit:
toughness built in long miles that carries into race day.
But cardio alone creates cracks in the system. High mileage spikes cortisol, wears down joints, and leaves muscles underdeveloped. Your engine may be strong, but without support, the frame holding it will collapse.
Strength: Building the Armor
Strength training is your armor, protecting the body so the engine can keep running. It provides:
Joint stability: stronger hips, glutes, and core keep your stride efficient.
Injury prevention: resilient tendons and ligaments resist breakdown.
Bone density: essential for female runners to prevent stress fractures.
Running economy: you burn less energy per mile, meaning faster, easier running.
Strength alone won’t carry you across 26.2. But it ensures your body can handle the pounding and still finish with power.
The Engine + The Armor = The Unbreakable Athlete
When cardio and strength work together, you stop being “a runner who lifts occasionally” or “a lifter who dabbles in running.” You become a complete athlete.
Here’s the difference:
Benefit | Cardio Provides | Strength Provides | Balanced Outcome |
Running Economy | Aerobic base | Neuromuscular strength | Race pace feels easier, less energy wasted |
Injury Resistance | Endurance foundation | Joint & muscle stability | Consistent training, fewer setbacks |
Fat Loss & Body Comp | Burns calories | Preserves lean muscle, boosts metabolism | Lean, toned, strong physique |
High-Intensity Performance | VO₂ max, stamina | Explosive power & recovery | Strong finishing kick, faster splits |
This is what balance looks like: homeostasis in training. The engine and the armor working in harmony.
Your Future Self
Picture yourself six months from now:
You’re on the start line of your next marathon.
Your lungs feel steady because your cardio base is strong.
Your legs feel powerful because strength training has armored them.
Your stride feels fluid because your body is balanced, not broken.
You don’t just finish. You finish strong. You run faster. You recover better. And when you see your race photos, you finally see the athlete you’ve become: lean, powerful, confident.
That’s your future self. And she’s closer than you think.
The KimFit Blueprint: Strength Training and Cardio
At Kim Miller Fitness, we don’t limit you—we empower you. The KimFit App gives you access to everything you need:
Running plans to build endurance, speed, and race confidence.
Strength training options up to 5 days per week, including upper body, lower body, full body, core, and mobility.
Prehab plans designed specifically for female marathoners.
You can run as many cardio sessions each week as you want—we’ll help you structure them so they support, not sabotage, your progress. And you’ll always have the strength workouts to back them up.
We encourage athletes to start with two days of strength training per week—to build a foundation without overwhelming your body. From there, you can gradually increase to three, four, even five days depending on your training cycle, race goals, and recovery.
But no matter what, one rule always applies: you must take at least one full rest day per week. No running. No lifting. Just rest. Because true progress doesn’t just come from training—it comes from recovery.
That’s the KimFit difference: everything you need, all in one system, built to keep you strong, fast, and unbreakable.
If you're ready to go beyond the basics and follow a structured strength program built specifically for runners, the KimFit app has you covered.
Just one of the many things you’ll find inside our app is our signature weekly workouts, which include:
20- and 40-minute daily sessions to match your schedule
Alternate exercises for all fitness levels
Minimal equipment needed—everything can be done from home
Strength programming designed to complement your running, not compete with it
Let us take the guesswork out of your cross-training. You focus on showing up—we’ll handle the rest.