3 Reasons Cardio Isn’t Going To Kill You: Part 2

Do endurance exercise and cardio cause heart attacks or plaque formation? Can cardio really kill you?  Find out the other two reasons why it won't.

Ben Greenfield,
December 28, 2015
Episode #266

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Last week, we took a deep dive into a topic based on this recent article and study reported on in the Wall Street Journal: is cardio is really going to kill you? You learned all about the study, and you also learned about the glaring fact that diet was completely ignored in the study. This week, we’re jumping straight back into the topic.

Let’s begin where we left off …

2) Intensity Matters

While the study acknowledges that intensity for longer periods of time can cause damage to the arteries, it fails to point out the fact that intensity for shorter periods of time can actually allow you to become just as fit without subjecting the body to voluminous stress.

For example, according to an one study on the effect of HIIT on oxidative enzymes responsible for increasing endurance, there were enormous increases in skeletal muscle oxidative enzymes in seven weeks in subjects who did four to ten thirty-second maximal cycling sprints followed by four minutes of recovery just three days a week.

Another six-week training study compared the increase in oxidative enzymes that resulted from either:

Four to six thirty-second maximal-effort cycling sprints, each followed by four-and-a-half minutes of recovery, performed three days a week (classic HIIT training) or forty to sixty minutes of steady cycling at 65 percent VO2 max (an easy aerobic intensity) five days a week. The levels of oxidative enzymes in the mitochondria in subjects who performed the HIIT program were significantly higher—even though they were training at a fraction of the volume of the aerobic group.

So how could this favorable endurance adaptation happen with such short periods of exercise? It turns out that the increased mitochondrial density and oxidative-enzyme activity (both significantly increase endurance) from HIIT are caused by completely different message-signaling pathways than those created by traditional endurance training. In the HIIT pathway, a “master switch” is activated that promotes the favorable endurance adaptation. This master switch is known as PGC-1-alpha, which stands for peroxisome proliferator-activated receptor gamma coactivator 1-­alpha. PGC-1-alpha causes that favorable increase in mitochondrial density and oxidative-­enzyme activity but can be activated by two completely separate signaling pathways—the calcium/calmodulin-dependent kinase (CaMK) pathway or the adenosine monophosphate-activated protein kinase (AMPK) pathway. Continuous, voluminous endurance training seems to activate the master PGC-1-alpha switch via the CaMK pathway, while intense interval training activates it via a completely different pathway: the AMPK pathway.

So ultimately, it turns out there are two different ways to train for a marathon or any other endurance activity: one method uses short, intense efforts, while the other uses the long, voluminous and often intense exercise the recent study found to be harmful to the heart.


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