This study was a meta-analysis of 15 randomized controlled trials that compared either habitual evening HIE or a single bout of evening HIE to no exercise. The 194 participants were healthy and had good sleep quality; 69% of them were fit and active.

Sleep quality was measured either objectively, via polysomnography and actigraphy, or subjectively, via standardized questionnaires. The primary outcomes were total sleep time (TST), time in bed (TIB), sleep efficiency (SE), sleep onset latency (SOL), wake time after sleep onset (WASO), and sleep architecture. The secondary outcome was subjective sleep quality.

🔍 Digging Deeper: Sleep terminology

Sleep architecture refers to the stages of a normal sleep cycle. It comprises REM sleep, which last 10 to 60 minutes, and the three stages of non-REM (NREM) sleep: N1 lasts minutes, just after falling asleep; N2 is a bit deeper sleep that lasts 10 to 60 minutes; and N3 is a deep sleep that lasts 20 to 40 minutes. (There used to be four NREM stages, but since no physiological or clinical differences could be found between N3 and N4, in 2007 the American Academy of Sleep Medicine combined these two stages.^[7])

Total sleep time (TST) is the sum of REM and NREM.

Time in bed (TIB) is the time spent in bed trying to sleep

Sleep efficiency (SE) reflects the difference between TST and TIB.

Sleep onset latency (SOL) is the time it takes to fall asleep, once in bed and trying to sleep.

REM sleep latency is the time it takes to reach the first REM sleep, once in bed and trying to sleep.

Wake after sleep onset (WASO) reflects sleep interruptions: how often you wake up during the night, and for how long.

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Does high-intensity exercise lead to worse sleep? Original paper