NIRS-based experimental evaluation of driver back fatigue during long-term driving

Figures & data

Figure 1. Example of driver postures while driving for a long time: Posture A (a); Posture B (b).

Table 1. Characteristics of muscle fiber types.

Fiber characteristics	Slow fibers (Type I, Slow oxidative)	Intermediate fivers (Type IIa, Fast aerobic)	Fast fibers (Type IIb, Fast anaerobic)
ATP use	Slowly	Quickly	Quickly
Capacity to produce ATP	Aerobic	Aerobic	Anaerobic
Concentration of capillaries	Extensive	Extensive	Sparse
Colour of fibers	Red	Red	White (pale)
Contraction velocity	Slow	Fast	Fast
Resistance to fatigue	Highest	High	Low
Fiber diameter	Smallest	Intermediate	Largest
Number of mitochondria	Many	Many	Few
Amount of myoglobin	Large	Large	Small
Primary fiber function	Endurance, maintaining posture	Medium duration, moderate movement	Short duration, intense movement

Figure 2. Oxygen concentration variation curve for the driver's lower back.

Figure 3. Driver's posture based on the seating status.

Figure 4. Mathematical model of lower-back fatigue.

Figure 5. Oxygen concentration variation curve for the drivers in this study.

Table 2. Result of the Spearman correlation analysis to investigate the correlation between the fatigue survey results and the NIRS signal results.

		S1	S2	S3	S4	S5	S6	S7	S8	S9
O2Hb	Correlation coefficient	0.771	0.779	0.732	0.927	0.793	0.639	0.935	0.634	0.725
	Sig.	0.015	0.013	0.039	0.000	0.011	0.064	0.000	0.067	0.027
HHb	Correlation coefficient	−0.104	−0.433	−0.620	−0.823	−0.830	−0.548	0.935	0.205	0.621
	Sig.	0.790	0.244	0.101	0.006	0.006	0.127	0.000	0.597	0.074
tHb	Correlation coefficient	0.771	0.606	0.620	0.927	0.793	0.730	0.935	0.634	0.725
	Sig.	0.015	0.084	0.101	0.000	0.011	0.025	0.000	0.067	0.027

Table 3. Results for the discomfort time point with the SEF90 value while driving for a long time.

Subjects	Posture	SEF90avg (min)	SEF90Freq. (min)	SEF90time (min)	Time constant (min)	Init–final (Freq.)	Max–min (Freq.)	Reliability (%)
S1	Posture A	25	30	20	35	0.420	0.667	64
S2	Posture A	35	35	30	88	1.237	1.263	12
S3	Posture A	30	30	40	56	1.107	1.287	77
S4	Posture A	20	20	15	45	0.793	1.023	54
S5	Posture A	30	30	25	42	1.133	1.213	50
S6	Posture A	40	45	35	24	1.137	1.137	72
S7	Posture A	35	45	40	37	1.220	1.360	80
S8	Posture A	30	35	30	48	1.193	1.397	73
S9	Posture A	30	50	45	56	1.583	1.583	80

Figure 6. Oxygen concentration variation curve based on the driver's posture.

Table 4. Results for the discomfort time points on the SEF90 value based on the driver's posture.

		SEF90avg (min)	SEF90Freq. (min)	SEF90time (min)	init-final (ΔSEF90)	max-min (ΔSEF90)	Reliability (%)
S10	Posture A	30	35	30	1.023	1.100	86
	Posture B	45	50	45	1.713	1.713	83
S11	Posture A	30	30	25	1.793	1.947	78
	Posture B	35	40	30	1.050	1.533	33

Figure 7. Mathematical model of lower-back fatigue based on the driver's posture (Time constant_T1).

Table 5. Information pertaining to the mathematical model on lower-back fatigue (subject 10).

		K (μmol)	α (sec^−1)	Time constant (T1)
S10	Posture A	12.5785	7.50E-04	1.33E+03
	Posture B	17.7715	6.00E-04	1.67E+03

Table 6. Relative discomfort times in each posture for subject 10 (Time constant_T1).

Time constant of position B (TB)	Oxygen concentration variation at TB (Δ)	Time point of Posture A having Δ
28 min	11.2335	50 min

Figure 8. Mathematical model of lower-back fatigue based on the driver's posture (Time constant_area).

Table 7. Times of relative discomfort in each posture for subject 10 (Time constant_area).

Time constant of Position B (TB)	Area of oxygen concentration variation at TB (Σ)	Time point of posture A having Σ
28	1.0896E+05	31

Table 8. Result of the relative discomfort time points on drivers’ postures.

		Time constantT1 (min)	Time constantarea (min)	Reliability (%)
S10	Posture A	50	31	86
	Posture B	28	28	83
S11	Posture A	15	27	78
	Posture B	42	42	33