There are countless studies showing that exercise drastically improves your health. However, there is an intense debate in the fitness community over whether steady state cardio (jogging for 20 minutes or more at around 60% to 70% of max capacity) or high intensity interval training (short sprint intervals between 15 seconds and 4 minutes at 90% to 100% of max capacity) is better for you. So, which is it: high intensity interval training (HIIT) or steady state cardio?
Let’s start with aerobic fitness levels. Studies have consistently found that high intensity interval training improves aerobic fitness to an equal or greater degree than steady state cardio (despite taking far less time). One meta analysis looked at studies of participants with coronary artery disease, heart failure, hypertension, metabolic syndrome and obesity. It found that HIIT increased VO2peak (a measure of aerobic fitness) by an average of 19.4%, versus just 10.3% for steady state cardio groups.
Of course, your training program will depend on what your goals are. However, High intensity interval training has been shown to improve even endurance athletes. One study, for example, had rowers train 7 times over a 4 week period. The HIIT group did 8 intervals of 2.5 minutes of rowing at 90% of their VO2peak, with individualized recovery periods. The researchers found that the HIIT group improved their 2,000 meter rowing time by 6.3 seconds (3.5 boat lengths) over the steady state group. The HIIT group also improved on every other tested measure including aerobic fitness levels.
Weight loss is the most contentious issue. Some studies have found that HIIT can reduce body fat to a similar or greater degree than steady state cardio. However, many others show the opposite. One meta analysis of patients with coronary artery disease found that participants who did steady state cardio lost more weight than those who did HIIT. Another study of overweight adults found that steady state cardio led to more body fat loss than HIIT. A meta analysis also found that steady state cardio led to more weight loss than HIIT. On net, it appears that steady state cardio beats out HIIT, but it likely depends on the exact HIIT program used.
While neither high intensity interval training or steady state cardio is going to add a lot of muscle, they differ in their interference with strength training. A study found that combining HIIT with a strength training program led to no decrements in strength or power. However, combining steady state cardio with a strength training program led to significant declines in strength and power (versus doing only strength training).
Resting Heart Rate:
A meta analysis found that steady state cardio reduces resting heart rate to a greater degree than HIIT.
Steady state cardio is great for cardiovascular health. However, a review found that HIIT improved vascular function, improved insulin sensitivity, reduced inflammation, and reduced oxidative stress to a greater degree than steady state cardio. Another study found that HIIT improved markers of cardiac function to a greater degree than steady state cardio. Specifically, HIIT led to greater improvements in endothelial function, insulin signaling in fat and skeletal muscle, skeletal muscle biogenesis, excitation-contraction coupling, and blood glucose and lipogenesis in adipose tissue.
Studies have found that high intensity interval training improves insulin sensitivity to an equal greater degree than steady state cardio. HIIT also appears to improve glycemic control to a greater degree than steady state cardio, indicating that it could be more protective against type 2 diabetes.
A number of studies show that steady state cardio reduces mortality risk. While some studies show that vigorous exercise can reduce mortality risk to a greater degree than moderate exercise, high intensity interval training has not specifically been studied to date.
Why choose just one? Both high intensity interval training and steady state cardio have advantages. Common HIIT programs include Wingate HIIT (30 seconds of “all out” intensity, followed by 4 minutes of recovery, repeated 4-6 times) and the Gibala regimen (60 seconds at 95% of VO2max, followed by 75 seconds of rest, repeated 8-12 times). So, start off doing high intensity interval training once a week and see how you like it!
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