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Over the past decade, the concept of high-intensity interval training (HIIT) has captivated the attention of the scientific community and health and exercise professionals alike due to its superior ability to improve cardiorespiratory fitness and cardiometabolic health for a lesser weekly time commitment relative to the current aerobic physical-activity guideline of moderate-intensity continuous training (MICT). As such, HIIT is frequently compared to MICT, but is it a fair comparison? Is one superior to the other? This article examines the research on each of these training methods to help you make better decisions when designing exercise programs for your clients.
As a health and exercise professional, you know that regular exercise yields an impressive array of health benefits ranging from improved cardiorespiratory fitness to greater blood glucose control. In fact, the scientifically proven health benefits of exercise are so robust it has led to the concept of exercise is medicine. Much like medications used to treat or prevent illness or disease, exercise programming is designed with a specific volume and intensity that is aligned with an individual client’s interests, physical attributes, health history and goals.
The two most common cardiorespiratory training paradigms are MICT and HIIT. In the scientific literature, there is generally a head-to-head comparison of MICT versus HIIT. However, this either/or approach can be problematic, as it infers that you should pick one or the other. It is important to remember that MICT and HIIT each provide unique health benefits. This notion was nicely illustrated in a few recent studies. In one paper, researchers found that HIIT was most effective at improving endothelial function and cardiorespiratory fitness. On the other hand, other research revealed that only MICT was effective at lowering body fat, blood pressure and lipids. Taken together, these findings highlight an important message for you and your clients: A range of volumes and intensities of exercise are needed for different health outcomes. Therefore, rather than choosing between MICT or HIIT, a more effective approach is to use a combination of the two.
It can be easy to forget that utilizing multiple forms of cardiorespiratory training, such as combining moderate- and vigorous-intensity workouts, is widely accepted and supported. As a reminder, the accepted guidelines for physical activity recommend 150 minutes of moderate-intensity exercise, 75 minutes of vigorous-intensity exercise OR a combination of the two. This pairing of HIIT and MICT has been shown to be as or more effective at improving cardiorespiratory fitness when compared to performing only MICT exercise.
In a previous ACE-supported study, we investigated the health and fitness benefits of two training programs for previously inactive adults. One program used an individualized approach, combining HIIT and MICT; the other program used a standardized, MICT-only program. Compared to the control group, both training programs yielded significant improvements. However, the combined HIIT and MICT group elicited significantly better improvements in cardiorespiratory fitness and cardiometabolic health when compared to the MICT-only group. Furthermore, the HIIT and MICT group produced more responders than the MICT-only group, likely due to the individualized nature of its programming.
Similarly, in another research investigation, we examined the cardiorespiratory fitness benefits of previously inactive individuals performing only MICT or MICT plus one weekly bout of HIIT. The MICT+HIIT group yielded two-and-a-half-times greater improvements in cardiorespiratory fitness when compared to the MICT-only group. Significantly, those who participated in the combination exercise group were more likely to stick with their program than those who only performed MICT.
When introducing a combination of HIIT and MICT into your clients’ programming, it is essential that you understand their current cardiorespiratory fitness levels and goals. With a new client, start with a baseline interview aimed at understanding their exercise history and health considerations. You should already understand your current clients’ cardiorespiratory fitness, but in both cases a cardiorespiratory fitness assessment should be considered for both new and established clients to identify their first and second ventilatory thresholds (VT1 and VT2) so that you can develop a personalized exercise program. The talk test is an effective assessment for most of your clients. With the knowledge gained from these assessments, you can develop a general program that includes HIIT and MICT.
In addition to identifying VT1 and VT2, remember that each client is unique with the types of physical activities they enjoy, as well as their goals, abilities and limitations. This will help you choose the best starting point for having both HIIT and MICT in their program. Below are programming examples for three different populations: young/middle-age and inactive; older with cardiovascular disease; and recreationally active. Each table includes four-week programs for clients who are starting a program with both HIIT and MICT.
HIIT and MICT each offer unique benefits and considering them as a spectrum can help your clients to continue exercising regardless of how busy their schedules might become. For example, if a client shares with you that the upcoming week will be busier than normal, you might adjust their programming to replace one of their MICT days with a HIIT day. The following figures present recommendations for utilizing the HIIT and MICT in varying situations.
While it may be effective, is the combination of HIIT and MICT something your clients will enjoy? Will they adhere to this unconventional type of programming? The ACE Mover Method is a great approach to asking open-ended questions that help your clients identify how they feel about their overall program. Maybe the HIIT intervals feel too long, or they enjoy the MICT exercises more than HIIT. Discuss any barriers that may be preventing your client from progressing as they should. Did they get a new job and have less time to exercise so they skipped a MICT workout?
Finally, collaborate and use your knowledge and what they have told you to come together and find the best plan moving forward. Maybe they need to set more realistic and attainable goals to get the ball rolling or they are doing well and feel ready to progress. Utilizing the ACE Mover Method sets you and your clients up for success because it helps you identify how to adjust their programming to ensure consistency and continuity, which is especially important when introducing a new approach such as combining HIIT and MICT.
