你的健康状况竟然可以用这个指标来衡量！

The most useful indicator of your overall health

反映你整体健康状况的最有用指标

“Heart-rate variability” has been decades in the making

“心率变异性”的研究已经开展了数十年。

Modern smart watches can measure all sorts of health indicators. Step counts and heart rates sit at the simpler end of the array, whereas VO2 max and blood-oxygen levels are of more interest to committed health nuts. But a category currently attracting particular attention is heart-rate variability (HRV).

现代智能手表能够测量各种健康指标。步数和心率属于其中较简单的一类，而最大摄氧量（VO₂ max）和血氧水平则更受执着的健康爱好者关注。但目前一个特别引人注目的类别是心率变异性（HRV）。

As its name suggests, HRV measures not how quickly the heart beats, but how regularly spaced those beats are. With heart rate a lower score is usually better, other things being equal, since it suggests a high level of cardiovascular fitness. When it comes to HRV, though, a higher number—that is, a more irregular pattern—is generally what you want.

顾名思义，心率变异性（HRV）衡量的并非心跳速度，而是心跳间隔的规律性。在其他条件相同的情况下，心率数值通常越低越好，因为这表明心血管健康水平较高。不过，就心率变异性而言，数值越高——即心跳模式越不规律——通常是人们所希望的。

HRV arises from the way the body regulates the heart. Left to its own devices, the heart will chug along at 100 beats per minute or so. That default rate is nudged up or down by the opposing halves of the autonomic nervous system (ANS), which acts unconsciously to control things like body temperature, breathing and digestion.

心率变异性（HRV）源于人体调节心脏的方式。如果不受干预，心脏会以每分钟约100次的频率跳动。自主神经系统（ANS）的两个相互对立的部分会使这个默认心率升高或降低，该系统在无意识状态下发挥作用，控制着体温、呼吸和消化等功能。

One half is the sympathetic nervous system, often known as the “fight-or-flight” system. This revs up the heart in response to things like exercise or fear or excitement. Its control is mostly exerted through hormones in the blood and neurotransmitters in the brain. That makes it a blunt instrument, and as the heart rate rises, so the time between beats becomes steadier.

其中一半是交感神经系统，常被称为“战斗或逃跑”系统。它会在运动、恐惧或兴奋等情况下让心脏加速跳动。其控制主要通过血液中的激素和大脑中的神经递质来实现。这使得它成为一种不够精细的调节方式，而且随着心率加快，心跳之间的间隔会变得更加规律。

The other half of the ANS is the parasympathetic, or “rest-and-digest” system. This slows the heart down when it is time to relax. It communicates with electrical signals sent via the vagus nerve. That allows precise control from moment to moment, which makes the time between heartbeats more variable. (Your heart rate speeds up slightly when you breathe in, for instance, and slows down as you breathe out.)

自主神经系统的另一半是副交感神经系统，也就是“休息与消化”系统。当需要放松时，它会使心脏减速。它通过迷走神经发送的电信号进行通信。这使得可以时刻进行精确控制，从而让心跳之间的间隔更具可变性。（例如，吸气时心率会略微加快，呼气时则会减慢。）

All else being equal, stress on the body boosts the sympathetic nervous system, decreasing HRV. All sorts of stress count, whether psychological or physical. A hard workout will cause HRV to fall for hours (or sometimes days) as your system recovers. So will lack of sleep, a cold, a failing marriage or worries about money.

在其他条件相同的情况下，身体所承受的压力会激活交感神经系统，降低心率变异性（HRV）。各种压力都算在内，无论是心理上的还是生理上的。一次高强度的锻炼会导致心率变异性在数小时（有时甚至数天）内下降，因为身体系统需要恢复。睡眠不足、感冒、婚姻破裂或对金钱的担忧也会产生同样的效果。

At a population level, higher HRV is a sign of an ANS that is in good nick, and a body that can adapt itself to the stresses of life. It is associated with a lower risk of heart attacks, and a higher chance of survival if you do have one. (It was in cardiology wards that HRV first proved its usefulness.) It is also associated with slower progression of dementia, less inflammation, a lower chance of suffering depression, and more.

从人群层面来看，较高的心率变异性（HRV）是自主神经系统（ANS）状态良好的标志，意味着身体能够适应生活中的各种压力。它与较低的心脏病发作风险相关，即便真的发作，存活几率也更高。（心率变异性的作用最初是在心脏病房得到证实的。）此外，它还与痴呆症进展较慢、炎症较轻、患抑郁症的几率较低等情况有关。

Most people will be more interested in what HRV can tell them about their personal lives. The best way to think of it is as an “accumulated stress” score. For sporty types a low HRV may be a signal that the body is struggling with too much training, and a hint to go easier in the gym for a while. But the numbers need careful interpretation. A big day out on the bike will cause a low HRV in the morning. But so will beers at the pub afterwards (alcohol suppresses HRV), or an unexpected tax bill waiting at home.

大多数人会更感兴趣的是心率变异性（HRV）能告诉他们关于个人生活的哪些信息。理解它的最佳方式是将其视为一个“累积压力”评分。对于热爱运动的人来说，较低的心率变异性可能表明身体难以承受过多的训练，这是一个暂时在健身房减少运动量的提示。但这些数值需要谨慎解读。骑车外出玩了一整天，第二天早上心率变异性可能会较低。但之后在酒吧喝了啤酒（酒精会抑制心率变异性），或者家里有一张意想不到的税单等着，也会导致心率变异性降低。

Those nerdy enough to track HRV may therefore want to keep a journal to refer to alongside the charts. Knowing what the numbers are telling you, after all, is the difference between mere data and its much more valuable cousin—useful information.

因此，那些痴迷到会追踪心率变异性（HRV）的人可能会想写日记，以便对照图表查阅。毕竟，明白这些数字在告诉你什么，正是单纯的数据与其更有价值的“近亲”——有用信息之间的区别所在。