The workout debate: experts weigh in on cardio vs. HIIT

For many, going out for a morning jog, a run with friends on the weekend, or hitting the treadmill at the gym, might be a fitness regimen staple. But in the last 10 to 15 years, HIIT workouts—high intensity interval training—have gained a lot of momentum, opening up a debate about which regimen actually provides a better workout or more health benefits.

HIIT workouts typically include an intense work phase that can last anywhere from a few seconds to several minutes, and are performed at a relatively high level, usually 80 to 95 percent of a person’s maximum heart rate. This is followed by a recovery phase that can last as long as the work phase but is performed at a lower intensity, usually around 50 percent of max heart rate. The work/recovery phases continue to alternate anywhere from 10 to 60 minutes, based on the program.

Celebrity fitness trainer Jillian Michaels explained to The Insider why cardio (in this case, running) is the least efficient form of exercise, saying in the piece, “this is because cardio is not metabolic, meaning it doesn't cause the body to continue to burn calories post-workout. Strength training, on the other hand, causes the body to burn calories both during and after a workout.”

Comparing interval training to moderate exercise

But, post-work out calorie burn aside, in clinical terms is HIIT really better than traditional cardio exercise, also known moderate-intensity continuous training (MICT)?

“Interval training has gained interest lately because research has suggested that you make similar gains in cardiovascular fitness as you would with traditional endurance exercise regimens, but with shorter periods of exercise,” said Neel Chokshi, MD, MBA, director of Penn’s Sports Cardiology & Fitness Program. “So, if you do not have time for the traditionally recommended 150 minutes of moderate intensity exercise each week, this may serve as a substitute. The ‘better’ exercise regimen is arguably the one that is consistent and sustainable to see gains over time.”

Kyle Meyer, DO, a Sports Medicine fellow at Penn Medicine, agrees, saying that one really isn’t better than the other. “The main difference between the two is in the time demand and the preference of the person,” he said. “Finding something that you enjoy and will continue is more important than forcing yourself to do an exercise that may have slightly different benefits.”

Meyer added, “HIIT has been shown to provide better results in cardiorespiratory fitness, and could be thought of as more efficient.” Chokshi and Chris Kusmiesz, MS, an exercise physiologist with the Penn Sports Cardiology and Fitness Program, agreed.

“Numerous research studies have shown that HIIT programs can yield similar cardiovascular improvements when compared to more traditional, steady-state exercise programs, like running or cycling,” Kusmiesz said.

In a 2014 study published in the British Journal of Sports Medicine (BJSM) a team from Queensland, Australia, and Trondheim, Norway, found that HIIT significantly increases cardiorespiratory fitness by almost double that of MICT in patients with lifestyle-induced chronic diseases such as coronary artery disease, heart failure, diabetes, hypertension, obesity and metabolic syndrome.

Another difference is that HIIT may improve VO2max to a greater degree, which means the heart and lungs are able to better deliver oxygen to working muscles. HIIT can also increase testosterone, which has been show to decrease with aerobic exercise like cardio. Testosterone affects the body’s ability to synthesize proteins, which helps to build muscle. While these differences are likely more relevant and important to high-level or elite athletes, even casual gym-goers may want to see some muscle toning results after putting in the hard work. Thinking more about the things that may be on the minds the more casual athlete, another potential factor for determining which workout routine could be “better,” would be impact on weight loss and risk for injuries.

The impact on weight loss and risk for injuries

“The explosive exercises, like sprinting, in HIIT would probably predispose a person more to muscle pulls, strains and tears,” said Kristopher Fayock, MD, associate program director of Primary Care Sports Medicine Fellowship and an assistant professor of Clinical Family Medicine and Community Health at Penn Medicine. “On the other hand, the longer, more repetitive activities in traditional cardio (jogging and distance running) would more likely predispose people to overuse skeletal injuries, like stress fractures.”

Fayock went on to note that in addition to injury risk, both HIIT and cardio can impact weight loss, provided diet is also taken into consideration.

“In general, weight loss is achieved through dietary calorie restriction, rather than just exercise,” Fayock said.

The standard exercise recommendation to maintain overall cardiovascular health is to accumulate 150 minutes of moderate intensity activity each week, as Chokshi mentioned. If the goal is weight loss, it requires a caloric deficit of 3500 calories to lose 1 pound—which is best accomplished through both diet and exercise. But if you are trying to lose weight by exercise alone, accumulating 350 to 450 minutes of cardiovascular exercise per week is needed in order to see results.

“There are a few studies that have indicated HIIT may be more beneficial than traditional low to moderate intensity cardiovascular exercise in achieving weight loss, but either option should always be used in addition to a healthy diet,” said Fayock.

Looking at long-term overall health

While it may seem obvious that the best thing to do for weight loss or weight maintenance is to balance a healthy diet with regular exercise, what some may not know is that any form of exercise—whether HIIT, cardio, walking, dancing, or yoga—can improve things like blood pressure, fat metabolism, and insulin sensitivity. The impact on these areas—which are major risk factors for lifestyle-induced diseases as mentioned in the BJSM study—will have the most lasting and positive impacts on one’s overall health.

Experts maintain, that regardless of what kind of exercise regime you prefer, the key takeaway is listening to your body to figure out what’s best for you and to understand what you can handle.

“Most healthy, young, active individuals are able to tolerate or adapt to HIIT programs. However, it is recommended that anyone become accustomed to moderate intensity exercise for several weeks to build a foundation of fitness before starting a HIIT program,” Kusmiesz said. And the same could be said for older adults, who are looking to increase or continue their exercise regimens as they age.

“There is a large amount of evidence showing that consistent aerobic exercise can help reduce the risk factors associated with cardiovascular disease,” he added. “If an older adult doesn't have any specific cardiac or musculoskeletal limitations, then they should be able to participate in a HIIT program or a scaled down version as needed, as long as the program is tailored to their individual body needs and goals.”

Overall, from the experts’ perspective, one exercise isn’t necessarily outright “better” than the other—the same way there isn’t one kind of magic diet that helps you quickly lose weight—but the best thing to do is find something that you like to do regularly, whether that’s running for 30 minutes a day or doing a one hour HIIT program three times a week. Meyer says, “In many cases, a blend of HIIT and traditional cardio might be the key to maintaining good overall health, increasing muscle strength, reducing cardiovascular risk and sustaining cardiorespiratory fitness.”