问题The question
HRV(心率变异性)常用来看身体恢复得怎样。我想让系统从第二天的 HRV 倒推出前一天哪件事做得不好,于是让 AI 比了四类模型,包括神经网络;数据是 2018 年以来 HRV 记录比较完整的约 2,300 天。HRV (heart rate variability) is a common sign of recovery. I wanted the system to work out from the next day's HRV which of the previous day's choices hurt it, so I had AI compare four kinds of models, including a neural network, on about 2,300 days since 2018 with reasonably complete HRV records.
结果The answer
单件事对第二天 HRV 的影响不到 1 毫秒,日常波动却有 ±5 毫秒,要几百个晚上才分得出来;神经网络也没有赢过简单的线性模型。唯一稳定的一条是多睡:多睡 1 小时,第二天 HRV 平均高 0.3–0.8 毫秒。我据此决定,网页不去猜“昨天哪件事让今天变差”。A single choice moves HRV by less than 1 ms while everyday swings are about ±5 ms, so it would take hundreds of nights to tell them apart, and the neural network did no better than a simple linear model. The one consistent signal was sleep: an extra hour went with 0.3–0.8 ms higher HRV the next day. So I decided the dashboard would not guess which of yesterday's choices made today worse.