HIIT vs. “Regular” Cardio

We’ve talked about high-intensity interval training (HIIT) before and explored some of its benefits; however, many people want to know how this method compares to trusted standards such as sustained, moderate-intensity endurance training (AKA “regular” cardio).

Any athlete or weekend warrior who has done their reading knows that fitness can be a hard thing to measure and, depending on who you talk to, the “best” way to get fit can vary wildly. 

In today’s post, we’ll go over what HIIT is and look at some of the research that’s been done comparing the effects of HIIT to good, old-fashioned “cardio.”

Okay, so what does HIIT involve?

When “cardio” comes up in conversation, most tend to think of exercises that involve a relatively sustained amount of effort over a moderate or long period of time. You can visualize a graph with effort over time as a straight line. 

HIIT, on the other hand, involves multiple short bursts of high-intensity work followed by short rest periods. Now, think of “waves” on a graph, with each peak being the high-intensity energy expenditure and the troughs as lower intensity outputs of effort. 

With HIIT, you tap into anaerobic energy stores. Because the workouts are so intense, they are often much shorter than a comparable cardio session. While a typical cardio session may last 20 – 40 minutes, most HIIT based workouts run between 7 – 20 minutes. The purported benefits of HIIT include improved fat-loss, improved cardiovascular fitness, and even decreased resistance to insulin (the mechanism that causes diabetes) (1).

How does HIIT compare to sustained cardiovascular exercise?

Multiple studies have been done comparing HIIT to continuous, moderate-intensity cardiovascular exercise. One study, looking at the effects of these two training regimens in mice, found that overall, both forms of exercise showed benefit. HIIT, however, was associated with a significantly more substantial increase in RNA and protein production associated with systemic improvements in metabolism (2).

In humans, the results between HIIT and traditional cardio have been mixed, and it often depends on what outcome is being measured. When assessing the effects of both regimens on body weight composition and fat loss in people, one study, which evaluated the results of 13 other included studies, found that there was no difference between HIIT and cardio (3). It did conclude, however, that HIIT was more time-efficient, as the HIIT participants spent an average of 40% less time training and achieved similar results.

Another study, assessing the cardiovascular responses of 12 young male participants, found that HIIT was associated with an approximately 10% higher cardiac output during exercise compared to traditional cardiovascular exercise (4). The cardiac output is a measure of the amount of work being done by the heart (it is the volume being pumped by the heart per minute). 

One meta-analysis, or summary of other research papers, found that the VO2max increase associated with HIIT was 5.5 mL/kg min vs. 4.9 mL/kg min for standard endurance training (5). VO2max is a marker used by researchers and athletes to measure the amount of oxygen being used during exercise. It is considered a marker of aerobic endurance or overall cardiovascular fitness. 

So, what does it all mean?

While research is still being done to assess the potential differences between HIIT and the traditional ‘cardio,’ current evidence appears to show:

• HIIT is associated with similar changes in body composition in obese participants, with 40% less training time
• In young male athletes, HIIT was associated with a 10% higher peak cardiac output during exercise compared to standard cardio
• Based on the analysis of multiple studies, HIIT appears to improve VO2max by about 10% more than standard endurance exercise

Taken in total, this may mean that HIIT can offer an at least comparable (maybe even better) workout as cardio, at a significantly lower time requirement. While HIIT is not for everyone (hey, it does say high-intensity right in the name), it appears to be a time-efficient alternative to traditional cardio routines.