Choosing an exercise program can be as difficult and confusing as choosing a diet. There are dozens out there, all claiming to be “scientific” and the best way to lose weight, get fit, and a number of other claims. What happened to good ole’ cardio? As it turns out, most of the exercise programs out there break down into a few simple categories — and once you understand the goals and benefits of each, you’ll discover that choosing and sticking to an exercise plan doesn’t have to be that difficult. In this article, we’ll wade through the “fad” and get straight to the “facts,” focusing on two popular exercise types — HIIT vs aerobic training — to help you decide which exercise plan is right for you.

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What is aerobic training?

Physical activity (i.e., exercise) essentially boils down to two types: aerobic and anaerobic.

• Aerobic exercise requires oxygen to generate energy. Aerobic exercise comprises endurance-type exercises, during which a person’s muscles move rhythmically and in a coordinated manner for a sustained period of time. Heart rate and breathing rate are increased during aerobic exercise. Examples of aerobic exercise include running, cycling and swimming.

• Anaerobic exercise does not require oxygen to generate energy. Instead, the body breaks down glucose stores for energy in the absence of oxygen, which causes lactic acid buildup in muscle. Anaerobic exercises involve short, intense bursts of physical activity. Examples of anaerobic exercise include weightlifting/strength training, sprinting and high intensity interval training (HIIT).

So, where does cardio (i.e., cardiovascular training) fit in? People often confuse cardio with aerobic exercise and use the two terms interchangeably; but the truth is, cardio is any type of exercise that raises your heart rate and breathing rate. That means that both aerobic and anaerobic exercise are cardio. To put it another way, all aerobic training is cardiovascular training, but not all cardiovascular training is aerobic training.

Weight loss vs. fitness

Weight loss is a major goal for individuals with prediabetes, diabetes, and other chronic conditions — and with good reason. Maintaining a healthy weight has several benefits, including: 

• Reduced blood pressure 
• Reduced risk for cardiovascular disease 
• Increased insulin sensitivity
• More energy
• Improved mobility
• Better mood
• Increased self-confidence

Restricting your caloric intake is the way to weight loss: if you eat fewer calories than you burn, you will — eventually — lose weight. However, the Centers for Disease Control and Prevention (CDC) cautions against losing weight too quickly and recommends a combination of healthy eating and exercise to safely and effectively get to a healthy weight.

Researchers also caution that losing weight shouldn’t be the only gauge for health and fitness. In fact, they demonstrate that it is more beneficial to health to focus on physical fitness rather than weight loss alone because people experience the metabolic benefits of exercise even in the absence of weight loss. This is because several factors — nutrition, sleep, stress, and hydration — impact your ability to lose weight. Another important consideration is that muscle is denser than fat, meaning that a pound of muscle takes up less physical space than a pound of fat. So, as you lose fat and build muscle, you might not lose weight — or not as much weight as you’d hoped. 

What is cardiorespiratory fitness?

So if fitness is a better measure of health than the number on the scale, how do we measure it?

Cardiorespiratory fitness, “the capacity of the circulatory and respiratory systems to supply oxygen to skeletal muscle mitochondria for energy production needed during physical activity,” is typically used to assess the relationship between physical activity and health status. Improved cardiorespiratory fitness has been linked to reduced risk for several diseases, including cardiovascular disease, obesity, diabetes and cancer. Low cardiorespiratory fitness is a risk factor for cardiovascular disease mortality — and, as such, is increasingly recognized as an essential measurement in regular health screenings.

One important goal of any exercise program is to maximize cardiorespiratory fitness, and there is strong evidence that both aerobic and anaerobic activity can help you meet that goal. But is one type of exercise better than the other? Fierce adherents on either side might lead you to believe that you must choose one. The science isn’t so black-and-white, however.

What is HIIT training?

HIIT — high intensity interval training — has taken the exercise world by storm because it promises the same (or better) cardiovascular benefits as moderate intensity continuous training (MICT) but in a much shorter time frame. Comprising bouts of short-duration, high intensity exercise alternating with rest or very low energy output periods, HIIT technically fits into both the aerobic (recovery phase) and anaerobic (intense activity phase) exercise categories. 

MICT, on the other hand, is truly an aerobic effort. It can be performed at low, moderate or high intensity, and typically lasts for 30 minutes or more. An effective HIIT workout, however, can be completed in 10 minutes — making it an attractive alternative for busy individuals juggling work, family and other commitments. And the science suggests that despite the minimal time commitment required to get in a good workout, the benefits are many:

• HIIT can reduce hyperglycemia (i.e., high blood sugar) in people with type 2 diabetes (T2D).

• HIIT can reduce abdominal/visceral fat mass in overweight/obese post-menopausal women.

Compared to MICT, HIIT appears to be superior for maximizing cardiorespiratory fitness, particularly in individuals with compromised health:

• A 2014 meta-analysis of 10 studies done on people with cardiometabolic diseases (coronary artery disease, heart failure, hypertension, metabolic syndrome and obesity) showed a significantly higher increase in VO₂ peak (maximal oxygen uptake) with HIIT than with MICT.

• Similarly, a randomized clinical trial in women undergoing cardiac rehabilitation found HIIT was superior for increasing VO₂ peak.

However, these studies were performed on relatively small numbers of people, so results may not be generalizable to everyone. To that point, a study in heart failure patients found no significant difference between HIIT and MICT. Additionally, most studies have been done in men, and while studies do support HIIT in women for cardiorespiratory fitness, the beneficial impacts on insulin sensitivity — another important component of metabolic health — are not as extensive in women as they are in men.

Clearly, more studies are needed to fully understand the beneficial impact of HIIT on all measures of health (not just cardiorespiratory fitness). Some studies even suggest that personalized exercise plans comprising combinations of HIIT, MICT and traditional resistance training will yield the best results. 

Nevertheless, when considering only cardiorespiratory fitness, it appears that HIIT is superior to MICT. But keep in mind that studies comparing the two exercise regimens are simply comparisons, and the important thing is that both types of exercise improve cardiorespiratory fitness, blood pressure, resting heart rate, heart rate recovery, vascular function and arterial stiffness. It’s also worth noting that some longer-term studies suggest the advantage of HIIT over MICT may lessen over time. This is important, because HIIT may not be for everyone.

HIIT vs aerobic workouts: Why and when HIIT may not be right for you

Most studies show that HIIT is a safe exercise regimen for most people; however, as with any exercise plan, you should talk with your doctor before starting a new fitness regimen. Some people shouldn’t participate in HIIT if they have certain preexisting conditions or other clinical complications. If you have any of the following, then you should avoid engaging in HIIT:

• Unstable angina pectoris (chest pain caused by reduced blood flow to the heart)

• Heart failure associated with symptoms (such as shortness of breath) that severely impact your quality of life

• Heart attack in the last 4 weeks

• Coronary artery bypass graft or percutaneous coronary intervention in the last year

• Heart disease that limits exercise (valvular, congenital, ischaemic and hypertrophic cardiomyopathy)

• Complex ventricular arrhythmias or heart block

• Severe chronic obstructive pulmonary, cerebrovascular disease, or uncontrolled peripheral vascular disease

• Uncontrolled diabetes

• Blood pressure >180/110 

• Severe neuropathy

As long as you don’t have these conditions, evidence shows you can safely enjoy a HIIT exercise regimen. According to Mayo Clinic, HIIT is safe and can even be especially beneficial for older, overweight and diabetic individuals. Because the regimen can be intense, however, there are some general recommendations that can help make the transition easier for you:

• Don’t start all-out: if you rush into a strenuous exercise plan before your body is ready, you could injure yourself.

• Slow down if you feel like you’re overdoing it.

• Avoid high-impact movements, jumping movements or heavy weights if your body can’t handle them. There are plenty of HIIT workout options that don’t include these movements.

Key takeaways

Exercise, by increasing cardiorespiratory fitness, is one of the best ways to reduce the risk for chronic diseases such as diabetes, metabolic syndrome, cardiovascular disease and obesity. But what about HIIT vs aerobic training? Research suggests that HIIT training results in more drastic improvements in cardiorespiratory fitness compared to lower-intensity, longer-duration workouts. Given those benefits, and the fact that a workout can be completed in as little as ten minutes, HIIT may be a great option for many people. However, HIIT is not for everyone, including those with certain heart conditions or those who simply aren’t interested in such a strenuous workout. If you prefer lower-intensity workouts, that’s just fine — as they, too, improve cardiometabolic health. The most important thing is just to move every day. If you do that, you’ll be well on your way to better health!