So, what’s the truth between these opposite points of view? Is there really a “right” time to do cardio, and will it crush your gains? The short answer: It depends on your goals.
Ask any “expert” when it’s best to include cardio in your workout and you’re sure to get answers ranging from “Do your cardio first to warm up” to “Never do cardio before leg day.” And, of course, there’s this: “Cardio kills your gains.”
However, the myth that cardio ruins your gains needs to go. Improving your cardiovascular health enhances recovery, reduces stress, and keeps you above ground longer.
For years, lifters have feared that running a few miles on the treadmill or a post-lift HIIT session would shred their hard-earned muscle. And while poor cardio timing can interfere with your progress, well-programmed cardio can actually complement it.
Here we’ll break down the science, debunk the fear, and show you when cardio helps, when it hurts, and how to structure it based on your goals.
Origin of the Cardio Myth
The idea that cardio kills your muscle gains didn’t come from the lab—it came from the gym bros.
Old-school bodybuilders viewed cardio as the enemy. It’s hard to argue with a muscular guy who believes anything more than five reps is considered cardio. Back then, the message was clear: If building muscle is the goal, cardio is a waste of time. Cardio was only something you suffered through to lean out fast during a cutting phase.
The way endurance athletes looked only reinforced the contrast. Lifters saw that look and thought, “That’s what cardio does? No thanks.”
This mindset grew even stronger in the early 2000s, when fitness culture split into two distinct groups: cardio bunnies who didn’t want to get bulky and lifters who did. Then influencers and gym-bros added fuel to that fire, dismissing steady-state cardio and warning everyone that it ruins your gains.
That fear stuck around, and what got lost in all the noise? Context.
Now it’s time to provide some.
How Cardio Really Helps Your Gains
Cardio isn’t the villain in your muscle-building quest. When it’s programmed and performed well, it’s a tool that supports fat loss, improves recovery, and boosts your work capacity.
Here are three good reasons to combine cardio with your lifting.
Fat Loss & Conditioning
If your main goal is to lose fat while keeping muscle, cardio can be your ally—but it’s all about timing and intensity. Doing cardio after lifting, when glycogen stores are low, can boost your fat-burning efforts. One 2015 study in Sports Medicine found that combining resistance training with post-lifting cardio improved body composition more than resistance training alone—without negatively impacting strength.
LISS: Low-Impact, High-Return
Low-Intensity Steady-State (LISS) cardio—such as incline walking, cycling, or light rowing—has little impact on strength or hypertrophy. It helps recovery by increasing blood flow to sore muscles, reducing stress, and improving sleep.
Heart Gains Are Still Gains
Better cardio equals improved work capacity. That means you can recover faster between sets, train harder during workouts, and keep your engine humming longer. That’s not “losing gains”—that’s optimizing them.
Cardio Timing Really Does Matter
Like many myths, there’s a sliver of truth buried beneath it. Cardio doesn’t automatically ruin gains—but it’s all about the timing.
High-Intensity Cardio Before Lifting? Not Ideal
If you jump right into sprints, hill intervals, or a long-distance run before lifting, you’re starting your lift fatigued. That’s a problem—especially for compound lifts that require maximum effort.
Here’s why:
- Your central nervous system isn’t as sharp.
- Muscle glycogen is partially depleted.
- Power output and lifting technique suffer, especially on lifts requiring explosiveness and stability. A 2016 Journal of Sports Sciences study found that doing cardio before strength training reduces strength performance.
The Interference Effect Is Real
The “interference effect” describes the competing adaptations that happen when endurance and strength training are not effectively combined. A comprehensive review in JSCR showed that concurrent training can blunt hypertrophy and strength development, primarily when modalities are performed back-to-back at high frequency and with poor sequencing.
It’s not about avoiding cardio—it’s about placing it where it fits. Before strength work, it may compromise performance. Afterward, it becomes a tool for recovery, conditioning, and body composition.
Goal-Based Cardio Timing
So, when are the best times to do your cardio? The best time to do cardio depends on your training goal, plain and simple. Here’s how to make it work for you.
For Fat Loss:
- When to Do It: After lifting, or in separate sessions.
- Why: You’ve already used your glycogen during strength work—now you can really tap into fat and glycogen stores, depending on whether you’re doing HITT or LISS.
- Bonus: Fasted morning cardio on off-days can enhance the deficit, if recovery is on point.
For Muscle:
- When to Do It: After weights or on rest days.
- Why: Your energy needs to go toward muscle growth. Don’t drain your CNS with high-intensity cardio first.
- Tip: 1–2 short LISS sessions per week is usually plenty to maintain conditioning when maximum muscle is the goal.
For Endurance:
- When to Do It: Prioritize cardio sessions and do strength work after or on alternate days.
- Why: Your performance hinges on aerobic output—lift to support durability and reduce injury risk
Here’s What Happens When You Believe Cardio Eats Your Gains
Thinking that cardio automatically cancels out strength gains has repercussions. Here’s how this myth causes problems with progress:
Lifters Avoid Cardio Altogether
Many strength-focused lifters eliminate cardio out of fear that it will “steal” their gains. But skipping conditioning means they’re missing out on the cardiovascular health, recovery benefits, and work capacity that actually support better lifting—being strong but winded after a single flight of stairs? That’s not performance; that’s your heart telling you to do your cardio.
Pushes False Either/Or Mentality
This myth promotes a black-and-white view: either you’re a “cardio person” or a “strength person.” That’s limiting. A balanced training plan can and should include both when timed and programmed well. Lifters who buy into the myth miss out on the benefits of becoming well-rounded athletes.
Miss Out on Health and Recovery Benefits
Cardio isn’t just about burning fat. It boosts heart health, circulation, blood pressure, and metabolic flexibility—key pillars of long-term performance and wellness. When you neglect cardio, these benefits diminish. Additionally, low-intensity cardio, such as walking or cycling, supports active recovery by increasing blood flow to sore muscles, clearing waste products, and delivering nutrients. That leads to better recovery between lifting sessions.
Stalls Fat Loss and Conditioning
Strength training alone often doesn’t provide enough of a metabolic boost to promote fat loss, especially in experienced lifters. Without some form of steady-state or interval-based cardio, your body has fewer tools to burn calories efficiently and adapt to longer-duration workouts due to a lack of aerobic endurance. This lack of endurance becomes apparent during cutting phases, when cardio is crucial for maintaining a caloric deficit without losing lean mass.
The Final Takeaway
Cardio doesn’t kill your gains—but poor planning might. The myth that cardio and lifting can’t coexist is like saying you can’t eat carbs and still get lean. It’s not about one or the other. It’s about smart sequencing.
If strength, size, or power is your main priority, lift first. That’s when your nervous system is sharp, your muscles are fresh, and your output will be highest. Cardio can come later—either at the end of your session or on separate days, depending on the intensity. On the flip side, if you’re training for endurance or working toward a race, prioritize cardio first and treat your lifts like performance support.
Cardio isn’t your enemy; it’s your ally when used at the right time, in the right way.
