Individual Patterns of Heart Rate Variability During Prolonged Cognitive Load with Mental Fatigue Induction

Figures

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  Figure 1. Experimental design. (a) Overall structure of the protocol: Pre-Test, BL, MFI, Post, Post-Test. (b) SST. (c) WMT. The asterisk (*) denotes the fixation point displayed at the center of the screen.

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  Figure 2. Dynamics of subjective fatigue ratings. (a) WAM scores before and after the SST and WMT. (b) SMFQ scores before and after the SST and WMT. (c) Dynamics of VAS fatigue ratings across successive 15 min blocks during the MFI stage in the SST and WMT. Hatching denotes SST, while the absence of hatching denotes WMT. The dashed and solid lines show the individual dynamics of subject #1 in the SST and WMT, respectively.

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  Figure 3. Dynamics of behavioral performance measures during prolonged mentally fatiguing tasks. (a) Distributions of standardized accuracy across blocks in SST and WMT. (b) Distributions of standardized reaction time across blocks in SST and WMT. (c) Distributions of the index of efficiency of mental performance (IES) across blocks in the SST and WMT. Dashed and solid blue lines show the individual dynamics of behavioral indices for subject #1 for SST and WMT, respectively. The red line serves as the threshold separating below-average from above-average performance.

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  Figure 4. Statistics of the identified phases of cognitive performance in SST and WMT. (a) Proportion of subjects exhibiting each phase. (b) Durations of the phases. The boundaries of each boxplot correspond to the first and third quartiles, the line inside the box indicates the median, and the whiskers show the minimum and maximum values in the sample.

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  Figure 5. Distribution of subjects by pattern of HR dynamics during task performance. The numbers above the bars show the percentage of subjects with each pattern.

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  Figure 6. Distribution of subjects according to the direction of the initial HR response during the SST and WMT: (a) ΔHR ≥ 0 group; (b) ΔHR < 0 group. Hatching denotes SST, while the absence of hatching denotes WMT. The dashed and solid lines show the individual ΔHR dynamics of subjects #2 and #3 during the SST and WMT, respectively.

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  Figure 7. Dynamics of HRV measures normalized to the BL values across the AP, OP, FP, and Post stages in the ΔHR ≥ 0 and ΔHR < 0 groups: (a) ΔHR; (b) ΔD; (c) ΔSI; (d) ΔLF; (e) ΔHF; (f) ΔLF/HF. Colors indicate the direction of the initial HR response (ΔHR ≥ 0 or ΔHR < 0): when an individually identified AP was present, ΔHR was determined for this phase; when AP was absent, the first 15 min task block was used. Hatching denotes SST, while the absence of hatching denotes WMT. Brackets denote model-based comparisons. Asterisks indicate statistical significance after Holm correction: p < 0.05 (*), p < 0.01 (**), and p < 0.001 (***).