Ask Tempo

Should I run with low HRV?

By Dylan, founder of Tempo · 4 min read

Short answer: a low HRV reading on its own isn't a stop sign — it's one input. Read it against how you actually feel, your sleep, and the shape of your week. A modest dip with good subjective feel usually means you're fine to run (maybe start conservatively); a big dip stacked with bad sleep and accumulated fatigue is a much stronger case to go easy. The number informs the call. It doesn't make it.

What HRV actually measures

Heart rate variability is the variation in time between your heartbeats. Higher variability generally signals your parasympathetic ("rest and recover") system is in charge; lower variability often means your body is under load — and that load can come from anywhere, not just training. Poor sleep, a glass of wine, a stressful day, the start of a cold, dehydration, travel, or simply a hard session yesterday will all push it down. That's the first thing worth internalising: HRV reflects total stress on your nervous system, not your training alone.

Read the trend, not the morning

One reading is noisy. Your own rolling baseline — and how far today sits outside your normal day-to-day swing — tells you far more than an absolute figure. A dip that's within your usual variation is mostly noise. A dip well outside it, especially holding low across several days, is the signal worth weighing. If you only ever react to single mornings, you'll chase ghosts.

When a dip is worth respecting

The case to ease off gets stronger when the low reading isn't alone: short or broken sleep, legs that feel genuinely heavy, a resting heart rate that's also elevated, or a few hard days already in the bank. When several of those line up, your body is telling you the same thing from multiple directions — and a hard session today buys less adaptation and more risk.

When you can probably proceed

A single low number with good sleep, fresh-feeling legs, and a normal resting heart rate is often just noise — or yesterday's session still clearing. Plenty of strong workouts happen on a slightly-low HRV morning. One sensible middle path: start the session and let the first few kilometres vote. If you warm up and feel strong, carry on; if the effort feels disproportionate early, you have your answer and can convert to something easier.

The honest limitation

HRV is a useful lagging indicator, not an oracle. Measured inconsistently (different time, posture, or device) it gets noisier still. It's at its best as one voice in the conversation — alongside your own read of your body, which no number can replace.