Eugene Teo takes on the PACER and challenges his cardiovascular fitness in a new video.

As a bodybuilding coach, Eugene Teo regularly shares advice on how to build strength and muscle safely and sustainably through resistance training—but when it comes to the cardio side of fitness, he is the first to admit his expertise is limited. In a new video on his YouTube channel, he steps out of his comfort zone with the progressive aerobic cardiovascular endurance run (PACER), also known as the multi-stage fitness test, or beep test.

The PACER consists of a series of shuffle runs of 20 meters, with the goal of each length being to reach the line before you hear the beep. The gap between each beep gets shorter and shorter as the test continues, until you are sprinting. When you are no longer able to complete a full 20 meters before hearing the beep, that means you're out of the test.

"I feel like I'm getting PTSD from this because of gym class back in high school," says Eugene. "I sucked at anything physical."

He's joined by trainer Sharelle Grant for the challenge. "I often find that I've got more physical strength in my legs than what I do in fitness," she says. "I can go hard, but I'll be absolutely destroyed at the end of it."

After a short warmup and taking in some high school pre-workout energy in the form of Nerds candy, Eugene and Sharelle begin the test—and hit failure at level 6, which they partially attribute to the fact that they're carrying a fair amount of muscle mass between them.

"I just hate that burning feeling," he says. "I could happily do low intensity cardio for hours... but when my lungs start burning, I tap out mentally."

Sharelle also points out that Eugene's running form was inefficient. "You're making it harder for yourself," she says. "You're very heavy on your feet, and you weren't using your arms to your full capacity to be able to get your stride and your pace." She adds that the PACER test is a good challenge, however, as it's quite difficult to incur injury as long as you warm up sufficiently.

"I've done VO2 testing before using a bike, which is easier because there's no skill," says Eugene. "But running, whether on a treadmill or outdoors or whatever, is very technical. I haven't run in years. And even if I had run in years, many people run, but they don't have good technique. It's a big skill."

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