❤️ **心脏健康评估**：通过主动代谢评估，包括测量最大摄氧量（VO2 max）和心率，可以客观了解心脏的健康状况和运动能力。VO2 max被认为是衡量心血管健康的重要指标，并可用于诊断潜在的心脏问题及制定个性化训练计划。定期进行此类评估有助于追踪身体变化和训练效果。

🔥 **燃脂与增肌的最佳速度**：文章指出，并非越快的速度就越有利于燃脂。研究表明，中低强度（心率和氧耗量处于较低区域）的有氧运动，即能进行对话的慢跑速度，是身体主要依靠脂肪供能的区间，最适合脂肪燃烧。而高强度运动（心率和氧耗量处于较高区域）则更多地依赖碳水化合物提供能量，但对于快速提升最大摄氧量和增加肌肉量有显著作用。

💡 **训练策略与心理调适**：根据评估结果，作者被建议将每周训练的80%用于中低强度有氧运动（Zone 2 & 3），以提高燃脂效率，并使身体更有效地利用能量。剩余的20%则建议进行高强度训练（Zone 4），以快速提升VO2 max和肌肉量。文章强调，克服心理上的不适感和“停止”的念头，是实现更具挑战性运动目标的关键。

📊 **身体成分分析的重要性**：在运动评估开始前，进行了身体成分分析，测量了肌肉、脂肪和水分的百分比。这有助于识别具体的健身目标，如减少体脂或增加肌肉。对于作者而言，目标是减少体脂同时保持肌肉量，这对于健康老龄化至关重要。

After running for over a decade, I wanted to see how healthy my heart is.I got an active metabolic assessment at Life Time, measuring my VO2 max and heart rate.I also learned which running speeds burn fat and build muscle.

I'm what I call an "on-paper" athlete. I've been running for a decade, I regularly take weightlifting classes, and I finished a marathon. In my mind, I should be ripped, shredded — all the paper metaphors that apply to human bodies.

Reality reveals some wrinkles. My running pace slowed down over the years, and I still can't do a real burpee. I recount the second half of the New York City marathon with the same gravitas people devote to speaking of real adversity.

So, I have no idea how "healthy" I actually am. To get to the heart of the matter, I decided to test my heart. I scheduled an "active metabolic assessment" through the athletic club Life Time. The AMA would measure my heart rate and my VO2 max — how much oxygen I consumed at different running intensities — to check how strong my heart is.

A high VO2 max is widely considered to be the "401K" of good health — something you should invest in sooner rather than later. Dr. Bradley Serwer, an interventional cardiologist and the Chief Medical Officer of a physician-led healthcare organization called VitalSolution, told me that VO2 max assessments are helpful in potentially diagnosing heart issues and can also be used to create personalized training plans.

"We're able to establish a baseline and then, with a mixture of training, hopefully see that VO2 max rises with time," Serwer, who is not affiliated with Life Time, said. The assessment would also show me which running speeds would help me burn fat, and which ones would build muscle and cardiovascular health, with the goal of increasing the speeds in both.

In the end, I learned I do need to challenge myself more — but luckily, not in the daunting ways I thought.

We started with a body composition analysis

Before we did anything, Donovan Stewart, a personal trainer at Life Time, performed a body composition analysis, which uses electrocurrent technology to measure my muscle, fat, and water content percentages. This could help me identify specific fitness goals, such as reducing fat or building muscle.

I'd gotten two body composition analyses before — one at the start of the year and one about eight months later. This third one confirmed that my main goal should be to lose a little bit of body fat without sacrificing muscle, which is necessary for healthy aging.

While extreme running can hinder muscle growth, Stewart explained that certain speeds can actually help runners bulk up. Knowing how often to run each speed could ensure that I hit my weight loss goals while also steadily gaining muscle.

My heart rate soared in anticipation

Stewartjoked that my heart rate was already high before I even stepped on the treadmill. As I tightened the heart rate monitor around my arm and pinched the oxygen mask around my nose, I realized I was nervous.

The plan was simple enough: I'd start off at a comfortable walking pace. Every two minutes, Stewart would increase my speed and incline, then ask me to rate the difficulty from 1 to 10. Once I hit my personal 10, the test was over.

It was more of a mental struggle

Even though I was straining to run faster than I ever had, I still didn't want to give up too soon. My brain was eyeing the ever-enticing "STOP" button on the treadmill, but my ego could always go 0.2 MPH faster.

As I ran, I reflected on the fact that I tend to talk myself out of doing more challenging runs because I hate being uncomfortable (with the exception of the marathon, in which FOMO overrode all my natural instincts).

I learned that if I can run it with a trainer and photographer watching, I should probably try to keep up the pace when I'm out on my own, too.

The best speed for fat loss isn't the quickest

After the assessment, Stewart broke down my personal cardio zones. He outlined which of my paces were a breeze, moderately challenging, and galloping-from-a-predator fast, all determined by my oxygen consumption and heart rate at different intervals.

To my surprise, faster speed doesn't equal greater fat loss, which is a common misconception, Stewart said.

I learned that zones 1 through 3 — ranging from a walk to a moderately-paced jog — are the best for burning fat. This is because the body primarily relies on fat for energy at this intensity.

People generally hit their VO2 max in zone 4, Serwer said, which is when a shift occurs. As one moves faster and reaches zone 5, their body stops getting enough energy from oxygen, relying more on carbohydrates for quick fuel.

Considering my goals, Stewart recommended that I spend about 80% of my weekly workouts focusing on zone 2 and 3 cardio. Since I was mostly running at a zone 2 pace, the goal is to gently increase my speed.

"You should be able to go out with a group and carry on a conversation for that long run," Serwer said. Doing so is "training your body to burn fat more efficiently."

Sprinting has its own benefits

While the assessment gave me an "optimal" VO2 max score, Stewart said he'd personally give me a slightly lower one based on his observations.

Serwer also said that VO2 max test results can vary because not all testing equipment is the same. Plus, even small factors like masks not being put on tightly enough can alter results. That's why he said it's a good idea to re-test every few months and look for consistent growth in the results.

"As a runner, you're going to want to improve your VO2 max," Serwer said. "You want to operate more efficiently so that your body uses less energy to produce the same results."

One way to quickly build up my VO2 max is to practice pushing myself more to the limit. Stewart recommended spending the other 20% of my week on zone 4 cardio, shaving off about a minute per mile in my speed. High-intensity cardio also puts more strain on my muscles, helping me build up muscle mass.

Days after the assessment, I sprinted around a local track field for the first time in my life. Just when I wanted to give up, my watch announced that I'd run my fastest mile ever.

I learned, begrudingly, that I can hit my more aspirational athletic goals. My brain just needs to get out of the way first.