Fatigue and Fatigability

Fatigue and Fatigability

• Concept of fatigability

• How it could be used in assessment and in evaluating responses to interventions

Individual’s Fatigue-Activity Relationship (Fatigability Function):

A Phenotype of Interest

Activity Level (physical, mental, social): effort x time.

FatigueLevel

Fatigability Can Limit Activity

Activity Level (physical, mental, social): effort x time.

FatigueLevel

A.Activity Limit

Tolerable Fatigue “Ceiling”

Fatigue and Physical Function Scores by Age:WHI Women ages 50-79

40

50

60

70

80

90

100

50-54 55-59 60-64 65-69 70-74 75+

Ene

rgy/

Fatig

ue s

core

Physical Function Energy/Fatigue

RAND-36 Energy/Fatigue subscale: “How much of the time during the past 4 weeks did you… feel full of pep? … have a lot of energy? … feel worn out? … feel tired?”

RAND-36 Physical Function subscale: “Does your health now limit you in these activities? If so, how much?”

• Vigorous activities, e.g., running, lifting, heavy objects, strenuous sports• Moderate activities, e.g., moving a table, pushing a vacuum cleaner, bowling, golf• Lifting or carrying groceries• Climbing several flights of stairs• Climbing one flight of stairs• Bending, kneeling, or stooping

•Walking more than a mile•Walking several blocks•Walking one block•Bathing or dressing myself

Activity Level (physical, mental, social): effort x time.

FatigueLevel

B A. .Old Activity Limit

Tolerable Fatigue “Ceiling”

New Activity Limit

Increased Fatigability Can Cause Disability

A goal for interventions to reduce fatigability:

To be able to do all that one would like to do over the course of the day, without feeling more fatigued than one is willing to tolerate

A goal for interventions to reduce fatigability:

To be able to do all that one would like to do over the course of the day, without feeling more fatigued than one is willing to tolerate.

A goal for interventions to reduce fatigability:

To be able to do all that one would like to do over the course of the day, without feeling more fatigued than one is willing to tolerate

How much activity you are willing to tolerate in a day is related to two dimensions of fatigability:

• Capacity: How much you can do before you get too fatigued?• Rate: How fast can you do it without getting too fatigued?

(Differing physiologic factors may affect capacity versus rate.)

Diurnal Patterns of Tiredness in Employed Women:Accumulation of Fatigue Over the Day in Older Women

Hour of Day

222120191817161514131211109876

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

“Tiredness”

50+

Under 30

30-49

Kahneman, Krueger, Schkade, Schwarz, & Stone, Science, 2004

Measuring Fatigue and Activity Over the Day

• ecological momentary assessment (EMA)• experience sampling method (ESM)• day reconstruction method (DRM)

References: • Shiffman S, Stone A, Hufford M. Ecological momentary assessment. Annu

Rev Clin Psychol 2008;4: 1-32 • Smith DM, Brown SL, Ubel PA. Mispredictions and misrecollections:

challenges for subjective outcome measurement. Disabil Rehabil 2008;30(6): 418-24.

• Murphy SL, Smith DM, Clauw DJ, Alexander NB. The impact of momentary pain and fatigue on physical acitivity in women with osteoarthritis. Arthritis and Rheumatism 2008; 59(6): 849-856

A goal for interventions to reduce fatigability:

To be able to do all that one would like to do over the course of the day, without feeling more fatigued than one is willing to tolerate

How much activity you are willing to tolerate in a day is related to two dimensions of fatigability:

• Capacity: How much you can do before you get too fatigued?• Rate: How fast can you do it without getting too fatigued?

Activity-rate-limiting fatigability can limit total daily activity and functional status

Hour

Number of activities done (ADLs, IADLS, etc.)

6 9 12 15 18 21

12

10

8

6

4

2

A

B

N.B. At any time during the day, individual A’s fatigue level equals individual B’s fatigue level.

A goal for interventions to reduce fatigability:

To be able to do all that one would like to do over the course of the day, without feeling more fatigued than one is willing to tolerate

• Some levels of fatigue are highly tolerable (e.g., during exercise).• Though scales of fatigue severity are valuable for several purposes,

dichotomizing between tolerable/intolerable can be useful, particularly for relating fatigue to activity and function.

Different daily activity profiles for persons acting at tolerable fatigue level

Hour

Number of activities done (ADLs, IADLS, etc.)

6 9 12 15 18 21

12

10

8

6

4

2

B

C

A

• Identify the daily activities that an individual needs to do (e.g., ADLs), plus additional ones that s/he wants to be able to do in the course of a day (exercise, other activities).

Capacities for Daily Activities with Tolerable Fatigue:Assessment

• Identify the daily activities that an individual needs to do (e.g., ADLs), plus additional ones that s/he wants to be able to do in the course of a day (exercise, other activities.

• Assess how many of them the s/he can do in the course of a day without feeling intolerably fatigued.

Capacities for Daily Activities with Tolerable Fatigue:Assessment

• Identify the daily activities that an individual needs to do (e.g., ADLs), plus additional ones that s/he wants to be able to do in the course of a day (exercise, other activities).

• Assess how many of them the s/he can do in the course of a day without feeling intolerably fatigued.

• Assess times and activities during which s/he experiences fatigue severe enough to stop or slow down.

Capacities for Daily Activities with Tolerable Fatigue:Assessment

• Identify the daily activities that an individual needs to do (e.g., ADLs), plus additional ones that s/he wants to be able to do in the course of a day (exercise, other activities.

• Assess how many of them the s/he can do in the course of a day without feeling intolerably fatigued.

• Assess times and activities during which s/he experiences fatigue severe enough to stop or slow down.

• Assessment could be based on self-reports (e.g., ecological momentary assessment), on observation, or by simulation methods (e.g., “Easy Street”)

Capacities for Daily Activities with Tolerable Fatigue:Assessment

• Identify the daily activities that an individual needs to do (e.g., ADLs), plus additional ones that s/he wants to be able to do in the course of a day (exercise, other activities).

• Assess how many of them the s/he can do in the course of a day without feeling intolerably fatigued.

• Assess times and activities during which s/he experiences fatigue severe enough to stop or slow down.

• Assessment could be based on self-reports (e.g., ecological momentary assessment), observation , or by simulation methods (e.g., “Easy Street”)

• Assessment instrument could generate a simple score that could be used to assess responses to interventions to reduce fatigability (relevant for drug indications, health care coverage policies).

Capacities for Daily Activities with Tolerable Fatigue:Assessment

• Identify the daily activities that an individual needs to do (e.g., ADLs), plus additional ones that s/he wants to be able to do in the course of a day (exercise, other activities.

• Assess how many of them the s/he can do in the course of a day without feeling intolerably fatigued.

• Assess times and activities during which s/he experiences fatigue severe enough to stop or slow down.

• Assessment could be based on self-reports (e.g., ecological momentary assessment), observation , or by simulation methods (e.g., “Easy Street”)

• Assessment instrument could generate a simple score that could be used to assess responses to interventions to reduce fatigability (relevant for drug indications, health care coverage policies).

• Does such an assessment instrument exist?

Capacities for Daily Activities with Tolerable Fatigue:Assessment

• Standard disability measures tell you if someone can or can’t do a a single task (e.g., walk a quarter-mile) with or without difficulty or assistance.

Capacities for Daily Activities with Tolerable Fatigue: Differences from Disability Measures

• Standard disability measures tell you if someone can or can’t do a a single task (e.g., walk a quarter-mile) with or without difficulty or assistance.

• They don’t tell you how much this ability is affected by the burden of other requirements for independent living, i.e.,

→ Even if you can walk a quarter-mile, are you too fatigued to do it after dressing, cleaning, and shopping?

→ Even if you aren’t too fatigued after dressing, cleaning, and shopping, do you do them so slowly in order to avoid fatigue so that you don’t have time to walk a quarter-mile after these activities?

Capacities for Daily Activities with Tolerable Fatigue: Differences from Disability Measures

• Standard disability measures tell you if someone can or can’t do a a single task (e.g., walk a quarter-mile) with or without difficulty or assistance.

• They don’t tell you how much this ability is affected by the burden of other requirements for independent living, i.e.,

→ Even if you can walk a quarter-mile, are you too fatigued to do it after dressing, cleaning, and shopping?

→ Even if you aren’t too fatigued after dressing, cleaning, and shopping, do you do them so slowly in order to avoid fatigue so that you don’t have time to walk a quarter-mile after these activities?

• Concept of capacities for daily activities with tolerable fatigue incorporates considerations of fatigability and speed in relation to disability. It may be a particularly meaningful outcome to many persons. (“Have a good day.”)

Capacities for Daily Activities with Tolerable Fatigue: Differences from Disability Measures