Jim Stoppani explains high intensity cardio and why fasted cardio doesn’t really work for most
Cardio remains one of the most debated aspects of fitness. While strength training often gets the spotlight for building muscle mass, cardiovascular exercise plays a crucial role in overall health, endurance, and fat loss. Yet many bodybuilders and fitness enthusiasts continue to ask the same question: What is the best type of cardio for losing fat without sacrificing muscle?
In a Generation Iron interview, renowned exercise scientist and fitness expert Jim Stoppani breaks down the science behind high-intensity interval training (HIIT), steady-state cardio, and the popular concept of fasted cardio. His explanation challenges some long-held beliefs about fat burning and reveals why many people may be approaching cardio the wrong way.
The Myth of the “Fat-Burning Zone”
For decades, fitness enthusiasts were told that lower-intensity cardio was the best way to burn fat. This belief stemmed from early exercise science research that suggested the body uses a higher percentage of fat for fuel during moderate, steady-state cardiovascular exercise.
As a result, many people spent hours jogging, cycling, or walking at a moderate pace in an effort to maximize fat loss.
However, according to Jim Stoppani, this interpretation of the research was incomplete.
While it is true that lower-intensity cardio utilizes a greater percentage of fat as fuel during exercise, that doesn’t necessarily mean it leads to greater overall fat loss. Modern research has shown that the total calories burned and the metabolic effects after exercise are far more important factors.
Why HIIT Cardio Is So Effective for Fat Loss
High-intensity interval training, commonly known as HIIT, involves alternating short bursts of maximum effort with periods of rest or lower-intensity activity.
During these intense intervals, the body primarily relies on stored carbohydrates (glycogen) and glucose for energy rather than fat. At first glance, this might seem counterproductive for fat loss.
But Stoppani explains that this is exactly why HIIT can be so effective.
By rapidly depleting glycogen stores, your body is forced to increase calorie expenditure and rely more heavily on fat stores after the workout is complete. This creates a powerful post-exercise metabolic effect commonly known as excess post-exercise oxygen consumption (EPOC), or the “afterburn effect.”
In simple terms, your body continues burning calories long after the workout ends.
HIIT vs. Steady-State Cardio
Stoppani points to research comparing short sprint intervals with traditional steady-state cardio.
In one study, participants performed either:
- Six to eight rounds of 30-second sprints
- Approximately 30 minutes of moderate-paced cardio
Despite spending significantly less time exercising, the sprint group achieved comparable fat-loss results.
The takeaway? Short bursts of high-intensity exercise can provide similar fat-burning benefits as much longer cardio sessions while requiring far less time.
For busy individuals looking to maximize results, HIIT offers an efficient and effective solution.
Does Fasted Cardio Burn More Fat?
Another popular fat-loss strategy is fasted cardio, which involves performing cardiovascular exercise before eating, typically first thing in the morning.
The theory is simple: if glycogen stores are lower after an overnight fast, the body will be forced to burn more fat during exercise.
While there is some truth to this concept, Jim Stoppani believes its benefits are often exaggerated.
Yes, fasted cardio may increase the amount of fat used for fuel during the workout itself. However, this does not necessarily translate into significantly greater long-term fat loss.
Why Fasted Cardio Isn’t the Magic Solution
According to Stoppani, the goal should not be to maximize fat burning during the workout. Instead, the focus should be on creating the greatest overall metabolic impact.
Since HIIT relies heavily on glucose and glycogen, it stimulates a larger post-workout calorie burn and greater metabolic adaptation throughout the day.
Fasted cardio, on the other hand, may limit workout intensity because energy stores are already lower. As a result, many individuals fail to achieve the same calorie-burning and metabolism-boosting benefits that come from higher-intensity training.
For most people looking to lose body fat, Stoppani argues that workout intensity matters more than whether or not you’ve eaten beforehand.
When Fasted Cardio Can Be Useful
Although Stoppani doesn’t recommend fasted cardio as a primary fat-loss strategy, he acknowledges that it may have value in specific situations. Competitive bodybuilders preparing for a contest often seek every possible advantage when attempting to achieve an extremely lean, dry appearance.
In the final stages of contest preparation, when body fat levels are already exceptionally low, fasted cardio may help provide a slight edge in conditioning and appearance.
At that point, competitors are no longer trying to lose large amounts of fat. Instead, they are making small adjustments to achieve maximum muscle definition and stage-ready conditioning.
For the average gym-goer, however, the difference is likely too small to have a meaningful impact on overall fat-loss results.
The Bottom Line
When it comes to fat loss, Jim Stoppani believes that high-intensity interval training is one of the most effective forms of cardio available. While steady-state cardio can still be beneficial, HIIT provides a greater metabolic boost, burns calories efficiently, and may produce similar fat-loss results in a fraction of the time.
As for fasted cardio, it isn’t the game-changing fat-burning strategy many people believe it to be. While it may offer minor benefits for advanced physique athletes looking to achieve peak conditioning, most individuals will see better results by focusing on workout intensity, consistency, nutrition, and overall calorie balance.
Ultimately, the best cardio program is the one you can perform consistently while supporting your long-term fitness goals.
Final Thoughts
Whether you’re trying to lose weight, improve conditioning, or prepare for a bodybuilding competition, understanding the science behind cardio can help you train smarter. Jim Stoppani’s insights reinforce an important lesson: fat loss isn’t just about what happens during your workout—it’s about how your body responds long after the session is over.
For more expert training advice, nutrition strategies, and fitness science insights, stay tuned to Generation Iron for the latest interviews, workouts, and educational content from the industry’s leading experts.
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