When it comes to the question, "Is it better to do cardio before or after a workout for fat loss?", opinions tend to vary—even among experienced fitness folks. As someone who's been through years of trial and error in bodybuilding, I’ve got some insights that might help clear things up.
Originally, cardio (which comes from the Greek word "kardia," meaning heart) was primarily used to strengthen the heart and prevent cardiovascular disease through moderate-intensity exercise. Over time, though, it’s become just as well-known for one other thing: burning fat.
When it comes to fat burning, the term “aerobic training” is actually more accurate than just saying “cardio.” The word “aerobic” comes from the Greek words “aēr,” meaning air or oxygen, and “bios,” meaning life. In simple terms, it refers to physical activity that relies on oxygen to produce energy.
In exercise, aerobic activities are those steady, moderate-intensity movements—like jogging, brisk walking, or cycling—that keep your heart rate up and rely heavily on oxygen to fuel your body.
Fat burning mainly happens through what's called aerobic metabolism (also known as oxidative metabolism), where your body breaks down stored fat using oxygen to create energy. This process, known as beta-oxidation, takes place inside the mitochondria of your cells and is one of the most effective ways your body taps into fat stores.
So, the best time to do cardio for fat loss is after your workout, and I highly recommend this approach. Here’s why it usually works better:
1. Muscle Glycogen Depletion
When you train hard—especially with weightlifting—you burn through your body’s glycogen stores (that’s the stored form of carbs in your muscles). Glycogen is your body’s go-to energy source during exercise. But once those reserves are used up, your body starts turning to stored fat for fuel.
So by doing your cardio after your main workout, you’re basically flipping the switch into fat-burning mode. First you burn through carbs, then your body taps into fat. It’s like a two-phase attack on body fat.
If fat loss is your main goal, I’d recommend doing post-workout cardio for 40 to 60 minutes. That’s enough time to really push your energy burn and maximize fat loss.
2. Hormonal Response
Lifting weights doesn’t just build muscle—it also triggers a hormonal response that helps burn fat. Training boosts the levels of several key hormones:
- Adrenaline and cortisol help break down fat for energy
- Glucagon encourages your body to use stored energy
- Growth hormone and testosterone help with fat metabolism and recovery
By doing cardio right after your workout, you’re taking full advantage of this hormonal environment—essentially riding the wave of your body’s fat-burning machinery.
Now, keep in mind—when you do your cardio isn’t the only thing that matters. If you really want to burn fat effectively and protect your muscle mass, you’ve got to keep an eye on your heart rate during cardio.
Here’s how to find your sweet spot:
First, calculate your maximum heart rate by subtracting your age from 220. Then, aim to stay at about 70% of that number during your cardio. This keeps you in the optimal fat-burning zone—intense enough to torch fat, but not so hard that your body starts breaking down muscle for energy.
Let’s take a quick example:
If you’re 40 years old:
220 - 40 = 180 (your max heart rate)
180 × 0.7 = 126 bpm — that’s your target heart rate for fat loss.
In short:
Doing cardio after your workout gives you a solid edge when it comes to burning fat. You’re tapping into fat stores, riding the hormonal boost from training, and increasing overall calorie burn. Just be sure to stay in that fat-burning heart rate zone to get the most out of it.
Stick with it consistently, and you’ll start seeing the results you’re working for. Stay focused—and enjoy the process!
Here is a video that shows a very unusual way to do cardio, perhaps one of the most effective ones 😂