How Do the Adaptations to Moderate-Intensity Continuous Exercise and High-Intensity Interval Training Differ?

April 14, 2024

by Cathe Friedrich

Exercise is a powerful stimulus for adaptation and the type of adaptations you get from your workouts depends on the type of exercise you do. For example, your heart and muscles adapt differently to strength training than a brisk walk.

Let’s look at the unique physiological adaptations you get from two forms of training: High-Intensity Interval Training (HIIT) and Moderate-Intensity Continuous Training (MICT) and how they differ.

Cardiovascular Adaptations: A Tale of Central and Peripheral Effects

A major difference between HIIT and MICT is the cardiovascular adaptations you get from each form of exercise:

HIIT: Focuses on central cardiovascular adaptations. This means it strengthens the heart itself, improving its ability to pump blood efficiently. HIIT workouts involve bursts of intense exercise followed by periods of rest or low-intensity activity. These intense bursts push your heart rate up significantly, forcing it to work harder. Over time, this strengthens the heart muscle and improves VO2 max, the maximum amount of oxygen your body can use during exercise.
MICT: Targets peripheral adaptations, focusing on how well your muscles use oxygen. MICT involves sustained exercise at a moderate intensity. This type of training improves the network of capillaries in your muscles, allowing them to extract more oxygen from your bloodstream. It also enhances the efficiency of your mitochondria, the powerhouses within your cells that use oxygen to create energy.

Metabolic Stress: A Key Driver of Metabolic Adaptations

Another key difference between HIIT and MICT is the type of metabolic stress they produce. HIIT, with its intense intervals, creates significant metabolic stress, so much so, that it prompts the body to adapt in ways that enhance metabolic health, such as improving insulin sensitivity and substrate metabolism. That’s why scientists and doctors believe HIIT improves markers of metabolic health more. For example, some studies show that HIIT training improves markers of glucose control more than MICT.

Research also shows that HIIT training is better for reducing visceral fat, including liver fat, which contributes to non-alcoholic fatty liver disease, previously known as NAFLD. Scientists have changed the name to metabolic dysfunction-associated steatotic liver disease (MASLD) because of the negative effects it has on insulin sensitivity and metabolic health.

MICT also has beneficial effects on your heart and markers of heart and metabolic health, but it may not have as profound of an effect, as it doesn’t create as much metabolic stress. Consequently, the adaptations that occur in response to MICT may not be as pronounced as those triggered by HIIT-induced metabolic stress. But don’t let that stop you from working out at a moderate intensity. Your body can’t work at top speed all the time. It’s all about balance.

Intensity and Enjoyment: Striking a Balance

Sticking to an exercise routine – that’s key if you want to reap all the benefits. But do you know what can make or break that long-term commitment? How much you enjoy the activity itself. Surprisingly, more and more research suggests that people enjoy HIIT more than MICT.

Why? Well, those short, varied intensity bursts during HIIT make the whole experience more engaging and you know it’ll be over quickly too! You’re not stuck in one monotonous pace the whole time. Variety is the spice of life, as they say!

Now, that’s not to say everyone feels that way. At the end of the day, enjoyment comes down to individual preferences and fitness levels. Some may find HIIT’s high-intensity too intimidating or challenging. While others prefer that steady-state comfort zone MICT provides. To each their own, right?

Time Efficiency: Maximizing Results in Minimal Time

HIIT strikes a responsive chord for people who are time strapped. HIIT sessions are shorter in duration compared to MICT sessions, yet they elicit similar or even greater physiological adaptations. This time-efficient nature of HIIT makes it an attractive option for individuals with busy schedules or those seeking to maximize their exercise benefits within a limited time frame.

But don’t discount moderate-intensity cardio (MICT) just yet. It’s an ideal option if you prefer exercising at a moderate pace for longer stretches or if you have limitations that make HIIT less ideal.

See, not everyone’s wired the same way when it comes to exercise preferences. Some love the steady-state groove of MICT workouts. Whatever the reason, MICT’s benefits are legit. It’s all about choosing what works for you. Plus, you don’t have to restrict yourself to one or the other. You can do both, just not on the same day.

The main thing is staying consistent with whatever exercise regimen you enjoy most. That’s the real key to unlocking mind and body gains. There’s more than one approach to exercising. Plus make time to add strength training to your routine if you want to stay fit and functional.

Summing It Up

Both HIIT and MICT can do a solid job boosting cardiovascular health and exercise capacity. But under the hood, they work a bit differently in terms of the specific physiological adaptations they create.

HIIT is excellent for triggering central adaptations that improve cardiovascular and metabolic health. MICT, on the other hand, is more about stimulating peripheral adaptations in the muscles themselves. And as mentioned, some people prefer a moderate, steady-state approach.

At the end of the day though, neither one is inherently “better.” The choice comes down to your individual needs and preferences – Are you chasing a specific fitness goal? What are your overall health considerations? Because both HIIT and MICT can certainly play a key role in a balanced, well-rounded training regimen.

It’s all about figuring out what mix of these exercise modalities works best for you personally. No one-size-fits-all here. Variety is key to continual progress anyway, right? Therefore, embracing a blend of HIIT’s intensity and MICT’s consistency could be the optimal strategy for most people.

References:

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“High-Intensity Interval Training Improves Glycemic Control, Cellular ….” 17 Jul. 2023, https://www.mdpi.com/1648-9144/59/7/1320.
“Understanding Liver Disease’s New Names—NASH is now MASH.” 07 Aug. 2023, https://liverinstitute.medschool.vcu.edu/news/understanding-new-liver-disease-names/.
“The physiology of interval training: a new target to HIIT.” 12 Dec. 2016, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5157059/.
“HIIT (High Intensity Interval Training) | The Nutrition Source ….” https://www.hsph.harvard.edu/nutritionsource/high-intensity-interval-training/.