Exploratory Assessment of Portable EEG- and PPG-Derived Indices Following High-Intensity Exercise Under Partial Sleep Restriction in Young Men

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Background/Objectives: This exploratory study investigated associations between partial sleep restriction and portable device-derived prefrontal EEG and PPG indices, heart rate recovery (HRR), and perceived exertion (RPE) after high-intensity exercise in young men. Methods: Forty healthy men were randomly assigned to a normal sleep group (NSG; ~8 h, n = 20) or a sleep-restricted group (SRG; ~4 h, n = 20). Participants performed the Harvard Step Test (HST). Prefrontal EEG (Fp1 and Fp2) and single-site PPG were recorded for 1 min before and immediately after exercise using a portable consumer-grade device. Heart rate (HR), HRR, RPE, and physical fitness were assessed. Data were analyzed using mixed-design analysis of variance, t-tests, and supplementary linear mixed-effects models with Holm correction. Results: The theta-to-beta ratio (TBR) showed a significant group × time interaction (Holm-adjusted p = 0.034), increasing only in the SRG (p = 0.0014), whereas spectral edge frequency at 90% (SEF-90) showed no interaction (p = 0.781). Significant interactions were observed for the heart rate variability (HRV) index (p = 0.0085), sympathetic-related index (p < 0.001), and parasympathetic-related index (p = 0.0063). The HRV index decreased and the sympathetic-related index increased only in the SRG, whereas the parasympathetic-related index decreased in both groups. During recovery (1–3 min), the SRG had higher HR and lower HRR than the NSG (all p < 0.05). RPE was also higher in the SRG (p = 0.013). All reported p-values were Holm-adjusted. Conclusions: Partial sleep restriction was associated with changes in prefrontal EEG and exploratory PPG-derived indices, lower early HRR, and greater perceived exertion. The selective TBR response suggests index-dependent EEG changes. These findings warrant caution because of limited EEG spatial coverage, brief recordings, potential artifacts, and unvalidated proprietary algorithms. Device-derived changes do not directly establish altered central or autonomic neural activity.