Table 4.

Fatigability measures representing perceived fatigue in the context of activity.

Measure	Components		Fatigability output	Level of measurement	Validity/Reliability
	Perceived fatigue	Activity
Severity of perceived fatigability (Barbosa et al., 2015)	• 7-point scale • 1 “extremely energetic” to 7 “extremely tired” • Immediately after activity	• 6-min walking test (6MWT)	Ratio of fatigue to distance walked in the 6MWT	Ratio	Not reported
Changes in perceived fatigue (Buchowski et al., 2013)	• 7-point scale • 1 “extremely more energetic” to 7 “extremely more tired” (4 “neither more tired or energetic”) • After defined physical activity task	• Physical activity tasks (e.g., moving objects with hands while sitting, moving a 0.5-kg weight while standing, walking across a 3-m room with turns	Fatigue score	Ordinal	Not reported
Perceived fatigability severity (Buchowski et al., 2013)	• 7-point scale • 1 “extremely more energetic” to 7 “extremely more tired” (4 “neither more tired or energetic”) • After defined physical activity task	• Physical activity tasks (e.g., moving objects with hands while sitting, moving a 0.5-kg weight while standing, walking across a 3-m room with turns)	Ratio of measured fatigue score to energy expenditure for each task	Ratio	Not reported
The Pittsburgh Fatigability Scale (Glynn et al., 2015) (instrument)	• 6-point scale • 0 “No fatigue” to 5 “Extremely fatigue” • Separate assessment of mental and physical fatigue	• 10 items for defined activity • Sedentary to moderate and high-intensity activity	• Summed mental fatigue scores and summed physical fatigue scores • Each score could range from 0 to 50	Ratio	Reliability • Cronbach’s alpha=0.88 • Test-retest reliability=0.86Validity • Good overall scale score discrimination in correctly classifying persons with high performance deterioration (AUCs, 0.68, p<.001) and high perceived exertion (AUCs, 0.73, p<.001).
Perceived fatigability (Gonzales et al., 2015)	• 7-point scale • 1 “extremely more energetic” to 7 “extremely more tired” (4 “neither more tired or energetic”) • After defined physical activity task	• 400-m walk	Ratio of fatigue score to energy expenditure during 400-m walk	Ratio	Not reported
Perceived fatigability (Lin, Roiland, Polesskaya et al., 2014)	• 18 items of visual analogue scale to evaluate fatigue severity (VAS-F) • Respond on a 10-cm analogue rating line ranging from 0 cm (not at all) to 10 cm (extremely) • Assessment before and after cognitive tests	• Cognitive tests (e.g., trail making test, Stroop color naming, digit span backward)	• Results of cluster analysis of difference in fatigue before and after cognitive tests • Results reported as high or low fatigability	Nominal	VAS-F internal consistency reliability • Before tests: 0.88 • After tests: 0.94
Perceived fatigability (Lin, Roiland, Heffner et al., 2014)	• 18 items of VAS-F • Respond on a 10-cm analogue rating line ranging from 0 cm (not at all) to 10 cm (extremely) • Assessment before and after 1- back tests	• 1-backtests • Including 10 visual sessions and 10 auditory sessions	• Yes/no responses • Use of repeated measure Anova • Significant main effect reported as fatigability (Yes)	Nominal	VAS-F internal consistency reliability • Before tests: 0.88 • After tests: 0.94
Mobility-Tiredness Scale (Manty et al., 2012) (instrument)	• Feeling fatigue or not feeling fatigue	• 2 items for defined activity (e.g., transferring from a chair or bed and walking indoors without another person’s help)	Yes/no responses	Nominal	Not reported
Changes in fatigue during high activity (Murphy & Smith, 2010)	• 5-point fatigue scale • Range of 0–4 (scale values not described) • Assessment at six specific time points each day (waking; +2, +6, +10, and +14 h; and 30 min before bed).	• Free-living activity • 4 h of high activity (1 SD above mean activity)	Difference in fatigue before and after high activity	Ratio	Not reported
Situational Fatigue Scale (Richardson et al., 2014) (instrument)	• 6-point scale • 0 “not fatigued at all” to 5 “extremely fatigued”	• 9 items for mental fatigue activity (e.g., reading magazines or newspapers for 1 h) • 4 items for physical fatigue activity (e.g., jogging for 20 min)	Summed ratings for each item	Ratio	Internal consistency reliability • Overall (Cronbach’s alpha = 0.90) • Mental fatigue items (Cronbach’s alpha = 0.89) • Physical fatigue items (Cronbach’s alpha = 0.88)Criterion validity • Moderate correlation with Fatigue Assessment Instrument (FAI): r = 0.47, p < .001
Rating of perceived exertion (RPE) at the end of a 400-m walk (Richardson et al., 2014)	• RPE on Borg scale • 6 “No exertion at all” to 20 “Maximal exertion” • Immediately after walking test	• 400-m walk	RPE score	Interval	Not reported
RPE after walking at standard speed (0.72 m/s) on a treadmill (Richardson et al., 2014)	• RPE on Borg scale • 6 “No exertion at all” to 20 “Maximal exertion” • Immediately after walking test	• 5 min of treadmill walking at 0.72 m/s	RPE score	Interval	Not reported
RPE after walking at subject-preferred speed on a treadmill (Richardson et al., 2014)	• RPE on Borg scale • 6 ‘No exertion at all” to 20 “Maximal exertion” • Immediately after walking test	• Walking at preferred gait speed for 5 min	RPE score	Interval	Not reported
RPE after walking test (Santasasto et al., 2014)	• RPE on Borg scale • 6 “No exertion at all” to 20 “Maximal exertion” • Immediately after walking test	• 5 min of treadmill walking at 0.72 m/s and 0% grade	• High fatigability: RPE ≥10 • Low fatigability: RPE <10	Nominal	Not reported
Perceived fatigability severity (Schnelle et al., 2012)	• 7-point scale • 1 “extremely energetic” to 7 “extremely tired” • Immediately after walking test	• 10-min walking test (10MWT)	Ratio of fatigue score to walking distance during 10MWT	Interval	Concurrent validity • Perceived fatigability severity measure was highly correlated with performance fatigability severity
Perceived exertion (Simonsick et al., 2014)	• RPE on Borg scale • 6 “No exertion at all” to 20 “Maximal exertion” • Immediately after walking test	• 5 min of treadmill walking at 0.67 m/s	High fatigability: RPE ≥ 10 Low fatigability: RPE <10	Nominal	Concurrent validity • Consistently strong associations with fatigue symptomsPredictive validity Robust association between perceived exertion and reported and observed function whether an RPE of 10 was used as a threshold or RPE was used as a continuous measure
RPE after walking test (Simonsick et al., 2016)	• RPE on Borg scale • 6 “No exertion at all” to 20 “Maximal exertion” • Immediately after walking test	• 5 min of treadmill walking at 0.67 m/s	Fatigue score	Interval	Not reported