Author(s): AYUSO-MORENO, R., LLANOS-MUÑOZ, R., LEO, F.M., TAPIA-SERRANO, M.A., GONZÁLEZ-PONCE, I., RUBIO-MORALES, A., Institution: UNIVERSITY OF EXTREMADURA - FACULTY OF SPORT SCIENCES, Country: SPAIN, Abstract-ID: 1329

INTRODUCTION: Mental fatigue (MF) in secondary education represents a psychobiological state induced by prolonged cognitive demands (1), yet its neurophysiological mechanisms remain understudied. Heart rate variability (HRV) reflects autonomic regulation and may indicate fatigue-related decrements (2). Spanish adolescents spend 78% of school time sedentary (3), creating conditions conducive to MF development. Physical activity (PA) shows promise for managing MF (4), but whether academic stress modulates HRV-fatigue relationships and how PA buffers these effects remains unclear. This study examined stress-dependent psychophysiological coupling and PA protective effects across the academic year.

METHODS: 168 secondary students (13-16 years, 51% female) wore Fitbit devices across 6 assessments spanning three academic terms: at term start (low-stress, n = 3) and term end coinciding with evaluations (high-stress, n = 3). Mental fatigue (VAS 0-100), HRV metrics (RMSSD, low-frequency power [LF], high-frequency power [HF]), and daily steps were measured continuously for approximately 7 days per assessment (N = 909 observations: 455 low-stress, 454 high-stress). Pearson correlations, independent t-tests, and group comparisons (median split: high PA >9385 steps/day) were conducted.

RESULTS: MF increased during high-stress vs low-stress periods (44.4±22.9 vs 38.5±21.1, p < 0.001***, d = 0.27), while HRV and PA remained stable (p > 0.05). Critically, among HRV indices, only LF correlated with MF during high-stress periods (r = -0.14, p = 0.007**) but not low-stress periods (r = -0.10, p = 0.068), demonstrating stress moderated autonomic-psychological coupling. PA correlated negatively with MF (low-stress: r = -0.26, p < 0.001***; high-stress: r = -0.10, p = 0.041*) and positively with LF (low-stress: r = 0.18, p < 0.001***; high-stress: r = 0.11, p = 0.036*). During high-stress periods, high-PA students showed 13% lower MF (41.2 vs 47.3, p = 0.004**, d = 0.27) and 16% higher LF (2382 vs 2045 ms², p = 0.012*, d = 0.26), suggesting preserved autonomic modulation.

CONCLUSION: LF-HRV specifically indexes MF under academic stress, revealing context-dependent neurophysiological mechanisms and differential sensitivity across HRV metrics. PA serves as a psychophysiological buffer maintaining autonomic function during high-demand periods. These findings support integrating movement into predominantly sedentary school schedules as a strategy to counteract MF and promote holistic well-being during this critical developmental period.

References: [1] Van Cutsem et al. 2017/ [2] Kim et al. 2018/ [3] Grao-Cruces et al. 2020/ [4] Chaddock-Heyman et al. 2018