Evaluate the effectiveness of cognitive stimulation and physiological dynamization on sleep inertia.

Introduction: Sleep inertia, characterized by impaired cognitive and psychomotor performance post-waking, poses a significant safety concern in operational settings, particularly when exacerbated by prior sleep loss. Existing reactive countermeasures demonstrate limited efficacy within the critical initial minutes following awakening. This study aimed to evaluate the effectiveness of two reactive interventions-cognitive stimulation and physiological dynamization -in mitigating sleep inertia, examining their impact after both a 9-hour time in bed baseline night and a 3-hour recovery night following total sleep deprivation. Methods: Forty-two healthy participants were randomized into Control, Cognitive Stimulation, or Dynamization (respiratory and muscular exercises) groups, performing a 5-minute countermeasure immediately upon awakening. Primary outcomes included Psychomotor Vigilance Test reaction times and attentional lapses, Karolinska Sleepiness Scale, and the Operational Assessment of Sleep Inertia State, measured at predefined intervals of 5, 20, 35, 40, 55 minutes post awakening. In the absence of a pre-protocol, true rested baseline, the 55 minutes measure was taken as the within-session reference point. Resutls: We confirmed that sleep inertia was significantly more pronounced following the 3-hour recovery night. Crucially, physiological dynamization significantly reduced sleep inertia within the first 20 minutes post-awakening, evidenced by lower reaction times (-49 ms, Cohen'd=0.81, p=0.02) and lapses (-2.3 lapses, d=0.71, p=0.02) at the Psychomotor Vigilance Task, and decreased subjective sleep inertia scores compared to the control group. Cognitive stimulation also conferred some benefits, notably reducing lapses and subjective sleepiness inertia scores, though its effect was not as consistent as that of dynamization. Participants in the cognitive stimulation group showed higher subjective and objective measures of sleep inertia after waking up, while no such significant differences were observed for the dynamization group. Conclusion: These findings indicate that physiological dynamization, incorporating brief respiratory and muscular exercises, is a highly promising reactive countermeasure for rapidly dissipating sleep inertia. Implementing such interventions post-awakening holds substantial potential value for enhancing immediate performance, though field studies are required to validate operational implications in demanding professional environments.