Why would sleep change a motor skill at all?
Practicing a movement makes you better in the short term, but something else happens afterward: the skill can keep improving or become more stable without any further practice. Researchers call this offline consolidation, meaning the memory of the movement is reorganized and strengthened after the training session ends, including during sleep. A 2024 review describes sleep-dependent processes as supporting the encoding of new motor memories and the consolidation of motor skills, with stage 2 sleep singled out as important for both [2].
The useful intuition is that sleep is not a single uniform state. It cycles through lighter stages, including stage 2, and REM sleep, when the brain is highly active and dreaming is common. If different sleep stages do different housekeeping for memory, then the stage a person spends more time in after practice could shape what kind of motor memory gets strengthened. That is the logic behind asking whether fine and gross skills depend on different stages, though the evidence supplied here does not settle the question.
In a complex gross motor task, REM sleep looked unhelpful
The most direct evidence here comes from a study of a complex gross motor adaptation task, the kind of whole-body skill where you adjust your movement to a new demand rather than refine a small precise action. In that study, REM sleep after learning seemed to counteract successful consolidation of the new gross motor skill, and the analysis also looked at sleep spindles and stage 2 sleep [1]. In plain terms, more REM sleep in that window was associated with less benefit from the training, not more.
That is a striking result because it runs against the simple story that sleep is uniformly good for motor learning. It is also a narrow result: it concerns one complex gross motor adaptation task, and the abstract-level evidence does not establish that REM sleep harms gross skills in general. The more careful reading is that REM sleep's role may depend on the type of task, and for this whole-body adaptation task it did not appear to help.
Does the fine-versus-gross split actually hold up?
The honest answer is that the supplied evidence does not test it. The gross motor study explicitly does not address fine motor skills [1], and the 2024 review discusses stage 2 and REM sleep in motor learning without differentiating between fine and gross skills [2]. So the common claim that fine skills lean on one stage and gross skills on another is not demonstrated by these sources; at best it is a hypothesis that fits the observation that a gross task showed an unusual REM pattern.
What the evidence does support is a more modest conclusion: stage 2 sleep appears important for encoding and consolidating motor skills generally [2], while REM sleep's contribution may be task-dependent, and in at least one complex gross motor task it seemed to interfere rather than help [1]. A reader trying to apply this should treat stage 2 as the better-supported stage for motor memory and treat claims about REM sleep as conditional on the kind of skill being learned.
What this means if you are trying to learn a motor skill
The practical takeaway is that sleep after practice is plausibly useful for motor memory, with stage 2 sleep the stage most consistently linked to consolidating motor skills in the evidence here [2]. There is no strong basis in these sources for deliberately targeting REM sleep, and the one gross motor study suggests that in some tasks REM sleep may not be doing the consolidating work one might assume [1].
The fine-versus-gross distinction, then, is a question worth asking rather than an answer the research has delivered. The studies supplied here point to stage-specific effects that vary with the task, which is consistent with the idea that different skills recruit different sleep processes, but it does not show that fine and gross skills are handled by different stages.
Sources used in this answer
The impact of diurnal sleep on the consolidation of a complex gross motor adaptation task
In a complex gross motor adaptation task, REM sleep after learning appeared to counteract successful consolidation of the new skill, and the study also examined sleep spindles and stage 2 sleep; it did not address fine motor skills.
Sleep, memory, and motor learning
Stage 2 sleep is described as important for encoding new motor memories and consolidating motor skills, with both stage 2 and REM sleep implicated in sleep-dependent offline motor skill learning, though fine and gross skills are not differentiated.