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Does Exercise Intensity Matter for Fat Loss?

There is no such thing as a universal best exercise routine. Period. Ok, now that that is out of the way, let’s use research to help answer the question in the title.

What intensity should you train at if you want to maximize fat loss? When losing fat, the goal is to retain muscle. If you want to maximize your results, you have to choose one. You can shed fat mass while bulking up. You can do a little bit of each — the amount depends on your starting point — but if you want to maximize fat loss, adding muscle needs to wait.

A recent systematic review and meta-analysis will help us answer the question. Keep in mind, research provides averaged results from specific participant populations. These are not universal, exact recommendations, rather, they are guidelines.

I repeat, there is no magic bullet or one-size-fits-all best approach to exercise. I don’t care how shredded the model was in the article telling you otherwise.

Interval Training vs. Moderate Intensity Continuous Training

When I first read this article, it was through the lens of a physical therapist. I am concerned about the health of my patients and body composition is one factor. Most of my goals center around pain, and while research is unclear whether BMI alone is a strong predictor of pain, excessive levels of body fat and visceral adiposity likely are. They are associated with cardiovascular diseases, metabolic disorders, cancer, and osteoarthritis.

Overweight and obese individuals are likely to be metabolically compromised. This means blood sugar control is poor. Many hormones responsible for hunger, building and maintaining muscle mass, and inflammation are directly influenced by the amount of fat we carry, particularly in the belly.

When designing exercise to lose weight, it’s important to target the correct weight — cut fat not muscle. If you dramatically drop your caloric intake and increase your activity level, you will lose fat, muscle, water, and possibly even bone mass. The scale should not be the only marker of success. Weight loss is not a ‘complete at all cost’ strategy.

Diet must be part of the equation for maximizing weight loss goals and maintaining results, but my primary concern in this article is exercise.

There are two primary training intensities people employ when designing an exercise program targeting weight loss: interval training (IT) and moderate-intensity continuous training (MCIT). The aforementioned systematic review defines them as follows:

MCIT: Moderate intensity of effort exercise (<80% peak heart rate or aerobic capacity) performed in a longer (relative to interval training bouts) single bout.

IT: Exercise performed in multiple shorter (relative to continuous training) bouts interspersed with recovery periods either at lower intensities of effort, or as complete rest.

IT and MCIT come in many exercise forms. The key differentiators are intensity and rest breaks. When reviewing the research, you have to be clear with what you are searching for. Many studies compare these two training modes for their effect on fitness level, measured through aerobic capacity. Important, but I am currently focused on weight loss.

The clearest mud

The final analysis of the review study included a robust 56 articles for the qualitative analysis and 54 articles for the quantitative analysis. Many studies are stuck in the single digits. More studies mean more data to draw a (hopefully) clearer picture.

The picture is both clear and muddy.

There is no consensus on whether MICT or IT is superior for body stimulating composition changes (fat and fat-free mass). It is clear as the breadth and depth of the data suggest either mode is effective with little to no difference in results. It is muddy as t many studies favor each intervention.

This means individuality is key.

Just because two studies look at the same general intervention (such as interval training) does not mean the participants or the interventions were the same. Trained individuals improve slower than novices with little exercise background. Intervals on the bike are different than the treadmill. The duration of the trial (4 vs. 12 weeks) will impact the results. These are only a handful of potential variables to consider.

So, what can you take away from this article? Choose the exercise mode that best fits you.

Tips for using IT and MCIT

Before choosing your desired program, some foundational concepts need to be integrated. First, you should complete your exercise program at least twice a week if you have little training background and up to five times a week if you are experienced. Track your progress. If you are unable to recover and sluggish, reduce the number of sessions or intensity, improve the diet and sleep routine, or both. If the program is too easy, up the intensity or volume.

If going the MCIT route, your heart rate should stay between 50 and 80% of your max heart rate. Here is a chart to give you an estimate based on age. The total duration should be 20–60 minutes with intensity inversely matching time — as duration increases, intensity decreases.

IT is generally shorter than MCIT in total exercise time. You work at a higher intensity but in short bouts. An example is three to six 20-second max-effort sprints with 60 seconds of rest between sprints. Complete that set of three to six sprints three times with five minutes of rest between sets. The sprint can be running, biking, or rowing.

Those are the fundamentals. Now we layer in the individuality.

If you enjoy jumping on a bike and watching the Olympics, you can lose weight doing it. Again, the intensity needs to be appropriate for the task. The exercise should still challenge you metabolically.

If you are short on time, interval training is your friend. Applying Tabattas to everything isn’t the answer (the intensity is often too low), instead, track your heart rate and how challenging the exercise is for you. Apply intervals to any form of cardio. You can mix IT into a long walk or weekend hike.

It bears repeating, there is no one-size-fits-all approach to exercise or specific exercise goals. If you want to lose weight, exercise volume and intensity, diet, sleep, and stress must be considered. There are foundational concepts that can be universally applied — volume is king for building muscle, sugar is bad, sleep is good — but they need to be molded to the individual. With respect to intensity, determine the mode of exercise that fits you best.

Challenging your body consistently is the most important aspect of exercise when aiming for change. Don’t forget about your diet, sleep, and stress levels, as they dictate your ability to recover and maximize future training sessions. All of the variables can make losing weight challenging and overwhelming. Choosing the mode of your exercise shouldn't be one of the complications.


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