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The Great Cardio Debate: Interval Training vs. Moderate Intensity for Fat Loss


In a recent discussion, a client raised the topic of interval training, specifically the practice of alternating sprinting and jogging for set durations. She's all fired up because she's excited about starting her fat loss phase with us at The Michaud Method. And she just went to Orange Theory yesterday, where they claim interval training is a fat-burning wonder. Even though I didn't want to burst her bubble—I had to explain how high-intensity cardio, including intervals, might sabotage her calorie deficit by triggering intense hunger spikes. I delve into my golden rule of cardio: the magic of moderate intensity, like walking a minimum of 10,000 steps a day to keep those hunger pangs at bay. I even suggested wearing a fitness tracker and setting a timer at the office to take extra steps to boost her NEAT (Non-Exercise Activity Thermogenesis).

Walking home in the pouring rain after our session, I pondered, "Aren't I just as 'on-brand' as that Orange Theory instructor?" I greatly advocate moderate-intensity cardio for fat loss (in combination with weight training and calorie-conscious meal plans). Seeking answers, I embarked on an exploration of the available research.

But before we proceed, a brief clarification: In this discussion, the terms "interval" and "high-intensity" training are used interchangeably. With that distinction in place, let's delve into the intricacies of high-intensity or interval training, examining both its potential advantages and drawbacks.

But before we go any further, a quick heads-up: In this discussion, the terms "interval" and "high-intensity" training are used interchangeably. So, buckle up as we journey through the fitness world, exploring the highs and lows of interval training and questioning the status quo.

Firstly, let's delve into the positive aspect. For decades, interval training was believed to be the ultimate method for shedding fat. The people who boasted about this training method did not get this idea out of thin air. Or for the sake of capitalism. There was hard evidence to support the benefits of interval training as a means of fat loss.

Now, let's shift our attention to the less favorable example—the realm of the fitness space. This community is entrenched in dogmatic beliefs. Enter Brad Schoenfeld, a prominent figure in strength training who embarked on an educational journey to earn a legitimate Ph.D. in exercise science. His mission? To challenge long-standing weightlifting practices that had been accepted unquestioningly for generations.

Dr. Schoenfeld has been a beacon of high-quality, thought-provoking research that has shaken the foundations of the strength training community. However, rather than embracing the opportunity to reevaluate their fitness approach, a sizable portion of this community attacked him personally instead of revisiting their views.

Now, let's fast forward to 2021, when Dr. Schoenfeld and his team released a research paper, one that is poised to wield substantial influence. The focus of this paper? Comparing changes in body composition between interval training and moderate-intensity continuous training, specifically emphasizing their effectiveness for fat loss (study).

This paper represents a meta-analysis, the gold standard in research methodology. A meta-analysis aggregates data from all pertinent studies on a particular topic. It draws conclusions based on the combined findings.

Here's where dogma enters the picture—many individuals in the fitness world adamantly insist that high-intensity intervals induce a more significant reduction in fat mass compared to moderate-intensity continuous training. Some even claim it can contribute to increased lean mass.

However, it's time to rethink those beliefs.

The study defines moderate-intensity continuous Training (MICT) as moderate effort (less than 80% of heart rate or aerobic capacity) sustained in a single, longer bout. On the other hand, Interval Training (IT) involves multiple shorter episodes interspersed with recovery periods at lower intensities or complete rest. This can be further subdivided into High-Intensity Interval Training (HIIT) and Sprint Interval Training (SIT), with sprint intervals demanding maximal effort for a brief duration, while HIIT involves slightly lower intensity and longer durations.

Historically, this has been a contentious issue. A previous meta-analysis suggested that intervals led to a whopping 28.5% greater reduction in fat mass compared to moderate-intensity continuous training, providing ample ammunition for dogmatic fitness trainers. However, it's crucial to note that the study had significant flaws, so much so that the journal retracted the article—a rare occurrence in published research.

Dr. Schoenfeld's article, in contrast, stands as a comprehensive meta-analysis, lending it greater credibility. After applying stringent exclusion criteria, they meticulously reviewed over 2,000 papers and included fifty-six in their final analysis.

In summary, the key findings are as follows:

Changes in Fat Mass:

The argument favoring intervals has hinged on the concept of a greater Excess Post-Exercise Oxygen Consumption (EPOC), where your body continues to burn calories after exercise. However, this study suggests that the additional energy expenditure is negligible and unlikely to impact fat loss significantly. In their own words, "Taken as a whole, these findings suggest that the intensity of effort does not meaningfully influence changes in fat loss during exercise."

Changes in Body Composition:

Unlike non-exercising control groups, interval training and longer-duration exercise proved marginally superior. The typical difference was a mere 0.22 to 0.25 kilograms (about half a pound). However, none of these studies combined training with dietary intervention, highlighting that diet plays a far more substantial role in fat loss and body composition.

Region-Specific Fat:

Interval training advocates have often cited older studies claiming that intervals specifically target abdominal fat compared to steady-state cardio. This paper, however, refutes that presumption, suggesting that there is no such thing as "region-specific fat loss" when it comes to cardiovascular activity.

Changes in Lean Mass:

Unfortunately, unsurprisingly, neither exercise promoted significant muscle growth.

So, is this news encouraging or disheartening?

One could easily view these findings and feel disheartened that neither endurance nor interval training substantially affects fat loss. It underscores the importance of dietary changes for achieving fat loss and optimal body composition.

Alternatively, one could rethink their perspective and grasp two important takeaways:

1) Intensity of Effort Doesn't Matter:

Whether you opt for intense interval sessions or longer, moderate-intensity cardio contributes positively to your overall health. Now, you can choose the one that suits your schedule best. If you're short on time, opt for a 20-minute Peloton workout. Need a mid-day mental break? Go for a leisurely 60-minute walk or run. Both offer similar health benefits.

2) Being in a Calorie Deficit is the Weight Loss King

Dr. Schoenfeld's study highlights a crucial insight—one that aligns with these two age-old adages:

"You lose weight in the kitchen (diet), you look good in the gym (exercise)."
"You cannot outrun a bad diet."

Both reinforce that dietary choices influence more than interval or continuous training in fat loss and body composition.

In the dynamic realm of fitness, where entrenched beliefs often prevail, embracing the evolution of our understanding as a mark of growth is essential. Our journey today has navigated the landscape of interval training, shedding light on its proponents and skeptics within the fitness community, including myself. As we delved into the research, we unearthed valuable insights, with Dr. Brad Schoenfeld's extensive meta-analysis challenging the long-held assumptions about the role of interval training in fat loss. The intensity of effort during exercise may not hold the pivotal role we once believed it did. Instead, the enduring wisdom stands that weight loss happens in the kitchen. This underscores the importance of dietary choices in shaping fat loss and body composition, transcending the debate between interval and continuous training.

As we advance on our fitness journeys, let's wholeheartedly embrace the capacity to question what we think we know, consistently refining our approaches to achieve our health and wellness goals.


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