It was originally thought that the nap on E1 should primarily contain REM to ensure a successful adaptation. However, according to the Polyphasic Survey 2018[1], only 50% of adapted E1 sleepers managed to get REM in their nap. This shows that the afternoon nap is not guaranteed to deliver REM sleep. Based on the data above, it still seems possible to complete the adaptation to E1 with no REM in the nap. This is likely a result of those adaptees covering their REM need by their core, leaving their nap as just wakefulness sustainment.
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