Table 8.

Subjective scales used in the different studies: measurement frequency and fatigue thresholds.

Reference measure	No.	Measure frequency	Measure threshold
Karolinska sleepiness scale	14	10 min	Not stated
	19	3 min	Not stated
	25	1 min	Not stated
	13	10 min	Alert: ≤3; Fatigue: ≥7
	21	5 min	Alert: ≤4; Fatigue: ≥5
	23	5 or 10 min	Alert: ≤4; Fatigue: ≥7
	30	3 times/day	Alert: <3; Fatigue: >7
	33	5 min	Alert: ≤8; Fatigue: = 9
	18	Not stated	Alert: <3; Transition: 3–5; Fatigue: 5–7
	22	5 min	Alert: ≤4; Transition: 5–6; Fatigue: ≥7
	33	5 min	Alert: ≤7; Transition: = 8; Fatigue: = 9
	37	Unclear	Level 1: 1–2; Level 2: 3–4; Level 3: 5–6; Level 4: 7–8; Level 5: 9
	38	Unclear	Level 1: 1–2; Level 2: 3–4; Level 3: 5–6; Level 4: 7–8; Level 5: 9
Borg's rating of perceived exertion	45	10 min	13
	46	1 h	15
	53	10 min	15
	56	Unclear	18
	58	After each fatiguing task set	No fatigue: <7; Fatigue: ≥15
	51	1 min	Low: ≤9.5; Medium: 9.5–13.5; High: 13.5
	54	Unclear	Low: 6–11; Medium: 12–14; High: 15–16; Very high ≥17
	58	After each fatiguing task set	No: <7; Low: ≥7; Medium: ≥11; High: ≥15