Why Your Trainer Is Wrong About Cardio (And What Actually Works)

Let me guess what your trainer told you about cardio:

• "Do 30-45 minutes on the treadmill after lifting"
• "Keep your heart rate in the 'fat-burning zone'"
• "Cardio kills your gains"
• "HIIT is the only cardio worth doing"

Here's the uncomfortable truth: They're probably wrong.

Not because they're bad trainers, but because the fitness industry loves oversimplified rules that fit on Instagram posts. Real physiology is messier—and way more interesting.

The Myth: "Cardio Kills Your Gains"

This one drives me crazy because it's caused so many clients to avoid cardio entirely.

The origin? A few studies showed that doing high-volume endurance training (think marathon prep) can interfere with strength adaptations. Trainers ran with it and created a blanket rule: "Cardio = muscle loss."

The reality: Moderate cardio doesn't kill your gains. In fact, it can enhance them.

A 2022 meta-analysis in Sports Medicine found that adding 2-3 cardio sessions per week actually improved strength gains in untrained individuals. Why? Better recovery, improved work capacity, and enhanced nutrient delivery to muscles.

The key is dose. If you're doing 60+ minutes of intense cardio every day while trying to build muscle, yeah, you'll have problems. But 20-30 minutes, 2-3x per week? That's not killing anything except excuses.

The Myth: "Stay in the Fat-Burning Zone"

This might be the most persistent myth in all of fitness.

You've seen the chart on the treadmill: a magical "fat-burning zone" at 60-70% max heart rate where your body supposedly torches fat most efficiently.

The truth: It's technically correct but practically useless.

Yes, at lower intensities, a higher percentage of calories burned comes from fat (about 60% vs. 40% at higher intensities). But here's what matters: total calories burned.

Let's do the math:

• 30 minutes in the "fat-burning zone": Burn 200 calories (60% from fat = 120 fat calories)
• 30 minutes of high-intensity work: Burn 400 calories (40% from fat = 160 fat calories)

You burned MORE fat at the higher intensity, despite the lower percentage. Plus, you get the afterburn effect (EPOC), continued elevated metabolism for hours after you're done.

The Myth: "HIIT Is Superior to Everything"

HIIT exploded in popularity for good reason—it's time-efficient and effective. But somewhere along the way, it became gospel: "HIIT or nothing."

The problem: HIIT isn't magic, and for many people, it's not even optimal.

Here's what trainers miss:

1. Recovery Cost

HIIT is stressful. Really stressful. If you're already lifting 4x per week and doing 3 HIIT sessions, you're accumulating massive fatigue. Your body doesn't distinguish between "workout stress" and "life stress"—cortisol is cortisol.

I've seen this pattern dozens of times: Client comes to me doing HIIT every day, eating 1,500 calories, sleeping 6 hours, working 50+ hours per week. They're exhausted, progress has stalled, and they want to do MORE HIIT to "break through."

That's not a training problem. That's a recovery problem.

2. Zone 2 Cardio Is Underrated

Low-intensity steady-state cardio (Zone 2, about 60-70% max HR) has made a huge comeback in performance circles, and for good reason.

Benefits trainers ignore:

• Builds aerobic base without crushing recovery
• Improves mitochondrial density (more energy factories in your cells)
• Enhances fat oxidation at higher intensities
• Actually aids recovery between intense sessions
• Sustainable long-term (try doing HIIT every day for a year—good luck)

The Myth: "Fasted Cardio Burns More Fat"

This one sounds so logical: no glucose available, so your body HAS to burn fat, right?

The reality: It doesn't matter for fat loss.

Multiple studies have shown that when total calories and protein are matched, fasted vs. fed cardio produces identical fat loss results. Your body doesn't care about the timing—it cares about the energy balance over days and weeks.

Plus, fasted cardio often means lower performance. If you can only do 20 minutes fasted but could crush 35 minutes fed, which burns more total calories?

When fasted cardio DOES work: If you hate breakfast and prefer training fasted, go for it. Personal preference matters. Just don't expect magic.

What Actually Works: The Science-Based Approach

After 13 years and hundreds of clients, here's what I've learned actually moves the needle:

1. Match Cardio to Your Goal

• Pure fat loss: Mix of HIIT and LISS, focus on creating a calorie deficit
• Performance: Periodized approach—build aerobic base, add intensity closer to competition
• Health/longevity: Mostly Zone 2 with occasional higher intensity
• Muscle building: Minimal but present—2-3x per week, moderate intensity

2. Consider Your Recovery Capacity

A 25-year-old single guy who sleeps 8 hours can handle way more volume than a 45-year-old parent working 60-hour weeks.

Your cardio needs to fit your life, not some Instagram influencer's program.

3. Progressive Overload Applies to Cardio Too

You wouldn't bench press the same weight forever. Don't do the same 30-minute treadmill walk at 3.0 mph for six months.

Progress could mean:

• More time at the same intensity
• Higher intensity for the same time
• Less rest during intervals
• Better perceived exertion at the same output

4. Daily Movement Trumps Formal Cardio

This is the biggest game-changer for my clients.

Getting 10,000+ steps per day does more for fat loss and health than any 30-minute cardio session. It's low-stress, doesn't interfere with lifting, and compounds over time.

I have clients who were doing 5 cardio sessions per week with mediocre results. We dropped it to 2 sessions but added daily walking. Fat loss accelerated.

Why? More total energy expenditure without crushing recovery.

The Bottom Line

Cardio isn't the enemy. It's not magic either.

It's a tool—and like any tool, it works when you use it correctly for YOUR situation:

• Match intensity and volume to your goals and recovery capacity
• Don't fear "killing your gains" with reasonable cardio
• Mix HIIT and Zone 2 for best results
• Prioritize daily movement over formal cardio sessions
• Stop chasing fat-burning zones and focus on total energy expenditure

The trainers who tell you cardio is useless? They're wrong.

The trainers who say you need an hour every day? Also wrong.

The truth is boring and unsexy: 2-4 cardio sessions per week, mixed intensities, combined with consistent daily movement and a reasonable diet will get 95% of people 95% of the results they want.

No extremes needed.