On days when I do some type of intentional strength or conditioning training, my schedule is fairly consistent: I train late morning or early afternoon, finish my last meal shortly after 4 PM, and am in bed between 8 and 9 PM.
My Polar watch (which I’ve been using for sleep tracking for a while now) generally shows a resting heart rate averaging somewhere in the low 50s over the first four hours of the night (which is the timeframe the watch uses to calculate recovery and sleep scores), with occasional absolute dips into the high 40s. My heart rate variability (HRV—variance between heartbeats that correlates to autonomic nervous system recovery) tends to run in the upper 40s to mid-50s. I often wake up feeling reasonably refreshed—so my subjective experience and the objective data seem to match.
Then there are Wednesdays.
Those are my Brazilian jiu-jitsu (BJJ) training nights. An average evening includes five to seven 5-minute rounds of “rolling” (live grappling sessions in which both partners are actively attempting to submit the other). It’s technical, physical, and about as far from a relaxed evening activity as I can get. We usually finish up by around 8 PM—and by the time I’ve changed, driven home, and showered, it’s close to 9:30 or 10:00 before I’m actually in bed.
The Polar data on those nights tells a very different story. Average resting heart rate lands in the upper 50s to low 60s, and HRV is in the mid-30s. The stiffness I feel the following morning isn’t surprising (that’s just the rolls). But the heart rate and HRV numbers are something else—the nervous system, still processing the effort while I’m trying to sleep.
What’s actually happening
Intense exercise triggers a cascade that is, by design, incompatible with sleep.
Your core temperature rises. Your body releases cortisol and adrenaline (the neurochemicals of effort and alertness). And your sympathetic nervous system (the “fight or flight” side of your autonomic nervous system) activates and stays activated. All of this is appropriate and useful during hard training. But the problem is that it doesn’t switch off the moment you step off the mat or leave the gym.
Your body needs roughly two to three hours after intense exercise to work through the process of reducing core temperature, normalizing cortisol levels, and allowing the parasympathetic (“rest and digest”) side of your nervous system to reassert itself. That’s the state in which sleep onset is easiest and sleep quality is best.
On normal training days, I’m finished with intense activity by noon or early afternoon and in bed six to nine hours later. By then, my nervous system has had all the time it needs to reset.
On BJJ nights, I’m asking my body to make that same transition in about 90 minutes. Of course, my heart rate and HRV numbers demonstrate that my request is on the submission end of the grappling match with nature—and the quality of my sleep dips as a result.
Research consistently supports this. A 2025 study published in Nature Communications (tracking more than 4 million nights of wearable data across nearly 15,000 adults) found that vigorous exercise within four hours of bedtime is associated with delayed sleep onset, shorter sleep duration, and reduced sleep quality, with effects growing more pronounced the closer to bedtime exercise ended. At two hours before sleep, maximal exercise was associated with a 14% drop in HRV and a 7% rise in resting heart rate. That’s my Wednesday night, quantified. (Light or moderate movement—an evening walk, easy stretching—doesn’t carry the same penalty. The same study found that light to moderate exercise ending more than two hours before bed had no meaningful effect on sleep.)
If you want the foundational case for why sleep quality matters at all, this earlier tip covers it well.
What this doesn’t mean
None of this is a reason to stop doing what you love. I still train BJJ most Wednesdays and climb most Fridays (a slightly less intense evening that also ends two to three hours before bed and produces in-between data).
Ultimately, the sleep trade-off is worth it to me. I’m not willing to give up either activity, and I’m not suggesting you should reorganize your life around a sleep score.
But there’s a difference between a trade you’re making consciously and a cost you’re absorbing without awareness.
If you train in the evenings (whether by choice or necessity), the data is fairly clear that it affects your sleep. Knowing that lets you manage your expectations and plan around it rather than just wondering why certain mornings feel harder than others.
Putting it into practice
If you have flexibility in when you train: earlier is better. Moving your workout ahead even thirty to sixty minutes (ideally giving your body at least three to four hours before bed) can make a meaningful difference in sleep quality over time. It might be worth trying if you’ve been treating your evening training time as fixed, when in reality it isn’t.
If evening training isn‘t going anywhere: a few smaller adjustments are worthy of experimentation.
First, keep your eating window earlier if you can. Even if training runs late, finishing your last meal a couple of hours before bed gives your digestion more time to settle before sleep. (This one’s easy for me on BJJ nights, since rolling with a full stomach causes its own problems.)
Second, end your workout with an actual cool-down rather than stopping abruptly. And when you shower after an evening session, try finishing with a slightly cooler rinse (even just 30 to 60 seconds of noticeably cool water can help accelerate the core temperature drop your body is already working on). (If the thought of a cold shower isn’t appealing, know that “useful cold” doesn’t have to be “extreme cold”—which I’ll discuss next week.)
And finally, if the following morning feels rough and your schedule allows, a nap is a very sound response to the situation.