CEU CORNER: Metabolic Training: Is Cardio Worth Your Time?

Many people think of “cardio” and “aerobic exercise” as one and the same. Sometimes cardio is described as “long slow distance” exercise, or any activity that raises the heart rate high enough for the exerciser to be working but still carry on a conversation. The American College of Sports Medicine (Garber et al. 2011) describes cardio as “exercise that uses large muscle groups and is done for 30–60 minutes.” In all of these cases, the type of cardio being discussed is moderate-intensity continuous training, or MICT.

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When asked, fitness professionals are almost unanimous in their confirmation that MICT is important. Many trainers and clients enjoy longer, more moderately paced workouts, such as a weekend run or a day of rails-to-trails bicycling. However, considering clients’ time-crunched schedules and the popularity of high-intensity interval training, the question becomes this: Are MICT workouts worth the time commitment? These workouts can take hours to complete. On the other hand, many respected health associations recommend MICT almost exclusively due to its proven ability to lower disease risk. But are other forms of exercise equally effective—or even more effective? And is MICT safe and effective for all participants? Some of the answers may surprise you.



What Is MICT (“Cardio”)?


Certainly, MICT has benefits for health, fitness and sports performance. It is also useful when trainers are working with special populations and when it is used as a modality for rehabilitation from heart attacks. In fact, the activity guidelines of many health associations feature MICT. For instance, the American Heart Association recommends 150 minutes per week of MICT, or 75 minutes per week of vigorous exercise, or a combination of both (AHA 2016). Examples cited include walking, jogging, swimming and biking. The AHA also suggests there is benefit even when the exercise is divided into segments of just 10–15 minutes, adding up to 30 minutes per day and done 5 days a week. The aerobic exercise recommendations of the ACSM (Garber et al. 2011) and the newly updated ones from the American Diabetes Association (Colberg et al. 2016) are identical to AHA’s with one exception: ADA also recommends 3 or more minutes of light activity every 30 minutes during “prolonged sedentary activities” to benefit blood glucose management, especially among people with type 2 diabetes (ADA 2013; ADA 2016). The U.S. Department of Health & Human Services also suggests a program of 150 minutes per week—and further acknowledges the benefits of increasing baseline activities such as standing, walking slowly, and lifting lightweight objects (2008). Several of these groups do mention nontraditional exercise, such as yoga, resistance training, boot camp and Pilates, but these forms may not be receiving the widespread attention they deserve. This is particularly important to note when we consider the research indicating that MICT may not be a good choice for all clients.


First, some studies have shown MICT to be ineffective for a percentage of individuals. In 1999, Bouchard et al. showed that different people who followed identical MICT exercise programs had dramatically different changes to their VO₂max2. (To review, VO₂max2 is the maximal oxygen uptake used during exercise, measured in milliliters of oxygen per kilogram of body weight per minute.) In this MICT study, the overall average increase in VO₂max2 was ~400 ml/kg/min, and some subjects improved their score by as much as 1,000 ml/kg/min. However, many subjects did not improve their VO₂max2.


Furthermore, it’s possible for MICT to cause negative effects in individuals. In 2012, Bouchard et al. used 1,687 subjects to investigate adverse physiological responses from the MICT protocol. The results show that 8.4% of subjects had an adverse change in insulin, 12.2% had systolic blood pressure increases, 10.4% responded adversely with triglyceride measures, and 13.3% showed a decrease in HDL (“good”) cholesterol levels. These adverse effects increase a person’s risk for diabetes and cardiovascular disease. Also, 7% of the subjects experienced more than one of these adverse responses. (The adverse response traits are independent of the improvement in cardiorespiratory fitness.) This is evidence that MICT is good for some clients, but not so for others.




What Is Metabolic Training?

Metabolic training generally refers to any type of high-intensity exercise that includes anaerobic training, such as interval training, Zone 3 workouts and resistance training, all of which will be discussed later in this article. Perry (2016) indicates that metabolic training is structural (spine-loading/core) and compound (multijoint) exercises with little rest between exercises, with the goal of maximizing calorie burn and increasing metabolic rate during and after the workout. Similarly, DuVall (2016) describes metabolic training as structured patterns of exercise and rest to produce a desired response from the body. And Verstegen (2013) states that metabolic training includes exercises that improve the capacity of energy systems—and thus, in the traditional sense, it is interval training.


A key benefit of metabolic training is increased excess post-exercise oxygen consumption (EPOC). EPOC can be defined as disequilibriums in physiologic function that lead to an increase in recovery metabolism (McArdle, Katch & Katch 2014). The increased calorie burn is caused by the body working overtime to get body functions back to resting metabolism. To do this, the body needs to resynthesize lactate to glycogen; reload hemoglobin with oxygen; start tissue repair; and redistribute calcium, potassium and sodium in the muscle cell (McArdle, Katch & Katch 2014). EPOC is dependent on the intensity and duration of exercise as well as the participant’s training status and gender (e.g. females have less muscle mass). Elevated post-exercise metabolism can last anywhere from 90 minutes to 24 hours.



What Is Interval Training?

Simply put, interval training is training that alternates between intense effort and periods of rest or lower-intensity exercise. Most of the time, when fitness professionals talk about metabolic training, they are referring to different types of interval training or training that involves both aerobic and anaerobic exercise. NASM Essentials of Personal Fitness Training (2017) states that cardiorespiratory training, in fact, must train both the aerobic and anaerobic energy systems in order to achieve its most common goals, which are


  • to improve health by reducing cardiovascular risk factors such as high body fat, undesirable blood lipids and high blood pressure;
  • to improve performance in sports, work and everyday activities;
  • to maintain a healthy weight; and
  • to reduce stress levels.


Interval training dates back to 1912, when Hannes Kolehmainen, a Finnish middle-distance runner, used race pace intervals to train for the Olympic 10,000-meter race. Later, Emil Zatopek—who was a gold medalist and Olympic record-holder in middle-distance races in the 1952 Helsinki Olympics—also used wind sprints with jog recoveries.


Robbins (2015) describes interval training as it relates to running intervals in preparation for races: Sprint 200 meters, recovery run 400–600 m, sprint 200 m and so on. This sequence can stress the anaerobic energy system while giving the body time to remove some waste products and replenish some energy. According to Robbins, the benefits of interval training also include


  • burning more calories in a shorter period of time;
  • avoiding monotonous exercise intensities;
  • improving cardiorespiratory efficiency; and
  • boosting EPOC.


Some types of interval training are zone training, Tabata, high-intensity interval training and moderate-intensity interval training.




Cardiorespiratory training must include overloading in order to trigger adaptations and improve metabolism. However, recovery is also vital, since it is during recovery that the adaptations actually occur (NASM 2017). For this reason, NASM suggests a type of interval training called zone training. Zone training involves alternating among three zones based on heart rate maximum, with HRmax calculated by the following formula: 208 – (0.7 × Age).


Zone 1 is exercise at 65%–75% of HRmax. Depending on level of fitness, a client can train in Zone 1 for a continuous 15–45 minutes. (In MICT, the exerciser essentially stays in Zone 1 for the entire workout.)


Zone 2 is exercise at 76%–85% of HRmax, which is usually close to a person’s anaerobic threshold. At the anaerobic threshold, the body can no longer meet its demand for oxygen, so anaerobic metabolism takes over. A client cannot train at this heart rate for long and may cycle back to Zone 1 for recovery.


Zone 3 is exercise at 86%–90% of HRmax. A client might be able to exercise for 30–60 seconds in Zone 3, then recover in Zone 1 or Zone 2 before repeating Zone 3. Training once a week in Zone 3 is generally enough to confer the benefits associated with Zone 3, while not risking overtraining. (Training in Zone 3 is a form of high-intensity interval training, or HIIT.)





Some fitness professionals are confused by the terminology used to describe high-intensity interval training and the studies done by Japanese researcher Izumi Tabata (1996).


HIIT is one of the hottest forms of training in the fitness industry (Thompson 2016). This training technique alternates between intervals of high-intensity effort and recovery. With HIIT, the work-to-rest ratio protocols that trainers can use with their clients are unlimited.


Tabata is a HIIT training protocol with specific guidelines: 20 seconds of all-out effort followed by 10 seconds of passive rest, done continuously for 4 minutes. Tabata used the protocol to investigate the effects of HIIT on the Japanese Olympic speedskating team. The team’s coaches wanted to know if a decrease in training volume and an increase in intensity could maintain or improve anaerobic capacity and VO₂max2. By the end of the study, the HIIT group had improved their anaerobic capacity by 28% and their VO₂max2 by 7 ml/kg/min.




One of the strongest arguments against performing MICT exclusively is that HIIT has been found to provide almost identical benefits but in a shorter amount of time (Gibala et al. 2012). In fact, HIIT research demonstrates that results similar to those of MICT can be achieved with up to 90% less training volume and 67% less time commitment (Comana 2014). Here’s a look some other HIIT research results.


  • Whyte, Gill & Cathcart (2010) worked with 10 men who were classified as overweight/obese and sedentary. Over the course of 2 weeks, the researchers had the men perform 6 sessions of 4–6 Wingate (30-second) sprints with 4.5 minutes of recovery between sprints. The results after 2 weeks showed that VO₂max2 and Wingate power increased and waist and hip circumferences decreased. Also, 24 hours postworkout, the subjects’ insulin sensitivity and resting fat-burning rate were higher, while their systolic blood pressure and resting carbohydrate burning were lower.
  • Hazell et al. (2014) had 15 recreationally active women perform 6 weeks of sprint interval training. The subjects did 4–6 (30-second) maximal sprints on a treadmill with 4 minutes of rest between sprints, 3 times per week. The sprint interval training decreased the subjects’ body fat by 8% and waist circumference by 3.5%. There were increases of 1.3% in fat-free mass, 8.7% in VO₂max2, and 4.8% in peak running speed. The researchers conclude that their training protocol is a time-efficient mode of training for decreasing body fat, increasing aerobic capacity, increasing peak running speed and increasing fat-free mass in healthy young women.
  • Tremblay, Simoneau, and Bouchard (1994) compared the effects of MICT exercise and HIIT on fat loss and muscle metabolism. The MICT group did 20 weeks of endurance training on a cycle ergometer, 4 then 5 times per week, 30–45 minutes per session, at an intensity of 60%–85% of heart rate reserve (HRR). The HIIT group did 25 half-hour aerobic training sessions at 70% of HRR plus 19 short interval sessions (starting with 10 sets of 15–30 seconds of work, increasing later to 15 sets) and 16 long interval sessions (starting with 4 sets of 60–90 seconds of work, increasing later to 5 sets). In sum, the MICT group did more than 80 sessions (over 40 hours total), while the HIIT group did 60 sessions (about 16 hours total).


The total calories burned for the endurance (MICT) group was greater, at 28,757.04, whereas the HIIT group burned 13,829.17—a difference of 14,927.87. The remarkable finding in this study was that while the HIIT group burned fewer calories, they decreased their subcutaneous fat far more than the MICT group did. The HIIT group also had a significant increase in enzymes promoting fat metabolism for muscle contraction. The bottom line: HIIT may confer greater fat loss and metabolism benefits than MICT, and in an abbreviated timeframe.



Making “Cardio” More Effective

For clients who don’t respond as well to MICT but enjoy this type of workout (distance runners, for instance), fitness professionals have many options for exercise programming. One option is to alternate workouts among MICT, high-intensity continuous training and HIIT. Here are two others.




Consider the findings of Ross, de Lannoy & Stotz (2015), who investigated the effect of different intensities and durations on improvements in VO₂max2. There were 121 middle-aged (average age 53.2 years) subjects in the study, all of whom had abdominal obesity. Subjects were assigned to one of three training protocols:


  • low-amount, low-intensity training for 30 minutes at 50% VO₂max2
  • high-amount, low-intensity training for 60 minutes at 50% VO₂max2
  • high-amount, high-intensity training for 40 minutes at 75% VO₂max2


The results indicate that increasing the duration or intensity of a training session can eliminate the problem of “nonresponders,” or people whose VO₂max2 is not improved by a MICT workout. In this study, 38.5% in the low-amount low-intensity group were nonresponders (their VO₂max2 did not improve). When the duration was doubled, only 17.6% (those in the high-amount low-intensity group) were nonresponders. And when both intensity and duration were increased, all of the participants showed improvements in VO₂max2.



Another way that trainers can help clients be responders is to have them perform resistance training. Not only is a benefit derived from burning more calories, but clients can also improve fitness, reduce weight and body fat, increase bone mineral density and improve self-confidence. Artero et al. (2012) did a review of literature on the effects of increased muscle strength and found that strength training has a protective effect against cancer and all other causes of mortality in healthy middle-aged men, men with hypertension and patients with heart disease. Westcott (2012) completed another review of the literature on resistance training, and he found that perks included improved sports and fitness performance, movement control, cognitive abilities, self-esteem, walking speed and functional independence (for elderly clients). Further, Westcott’s review indicated that resistance training can promote bone development, with studies showing a 1%–3% increase in bone mineral density. Also notably, he shared that weight training can reduce lower-back pain and the discomfort of arthritis and fibromyalgia.


Get Creative With Program Design

Even though many health resources recommend MICT for improved fitness and health, fitness professionals and clients should be aware that the benefits of other forms of exercise can be as good as—or better than—those of MICT. This is not to suggest that MICT does not have benefits; rather, it’s an indication that other forms of exercise can (and perhaps should) be included along with MICT in a total training program.


To summarize, cardio/MICT has been shown to reduce cardiovascular risk factors, improve blood lipid measures, lower high blood pressure, improve sports performance and reduce anxiety. But it is important to remember the research done by Bouchard et al. (1999) and Ross, de Lannoy & Stotz (2015), which showed that some people do not respond to MICT. For this group, increasing the intensity and duration of training may elicit the desired physiological response. From Tremblay, Simoneau & Bouchard (1994) to Hazell et al. (2014), we learned that interval training at high or moderate intensities produces very good results for burning calories during and after exercise, improving VO₂max2, increasing fat loss, reducing waist and hip circumferences, reducing systolic blood pressure and increasing fat-free mass. Further, weight training has benefits for almost every aspect of health and fitness, especially its role in increasing bone mineral density and weight loss. With so many options for exercise, fitness professionals shouldn’t hesitate to be creative with their programming in order to help their clients achieve all of their goals in a safe, effective and time-efficient manner.