Effects of Different Forms of Fatigue on Double-Task Performance in the Elderly

The dual task (walking and cognitive task at the same time) is increasingly used in geriatrics in protocols for detecting people who are falling and/or for highlighting cognitive disorders. However, frail elderly people tend to get tired quickly and a lack of awareness of the effects of fatigue on dual-task performance could alter the diagnosis. There are two types of fatigue: mental fatigue and peripheral muscle fatigue. Each participant will do both types of fatigue over 2 appointments spaced by 7 days so that the subject can recover from induced fatigue. The sequence of fatigue tasks will be randomized. At the first appointment (day 0): Pre-fatigue assessment : The subject must walk on 10m with round trip for 1min. the subject must do the arithmetic count of 3 in 3 Then comes the evaluation in double task (walking and counting at once for 1min). The subject must walk on 10m with round trip for 1min by doing the arithmetic count of 3 in 3 at the same time. mental fatigue task or muscle fatigue task (randomized) post-fatigue assessment (the same as pre-fatigue assessment) 7 resting days Second appointment (day 7) Pre-fatigue assessment : The subject must walk on 10m with round trip for 1min. the subject must do the arithmetic count of 3 in 3 Then comes the evaluation in double task (walking and counting at once for 1min). The subject must walk on 10m with round trip for 1min by doing the arithmetic count of 3 in 3 at the same time. mental fatigue task or muscle fatigue task (randomized) post-fatigue assessment (the same as pre-fatigue assessment)

First appointment : Pre-fatigue assessment mental fatigue task post-fatigue assessment 7 resting days second appointment Pre-fatigue assessment Muscle fatigue task post-fatigue assessment

First appointment : Pre-fatigue assessment Muscle fatigue task post-fatigue assessment 7 resting days second appointment Pre-fatigue assessment mental fatigue task post-fatigue assessment

Each participant will do both types of fatigue over 2 appointments spaced by 7 days so that the subject can recover from induced fatigue. The sequence of fatigue tasks will be randomized.

Dual task performance (DTEspeed motor performance; DTEcog cognitive performance) will be compared before and after a protocol of peripheral mental and muscular fatigue. For Dual Task Performance, the cognitive task performance (maximum count count - error count) performed alone (single ST task) and performed while walking (double ST task) will be compared.

Dual task performance (DTEspeed motor performance; DTEcog cognitive performance) will be compared before and after a protocol of peripheral mental and muscular fatigue. For Dual Task Performance, the cognitive task performance (maximum count count - error count) performed alone (single ST task) and performed while walking (double ST task) will be compared.

Young group Inclusion Criteria: 20 to 40 years old Exclusion Criteria: psychiatric disorders Severe hearing or vision loss Motor or sensory disability that may interfere with test completion Old group Inclusion Criteria: 65 to 90 years old less than 3 Fried's criteria of fragility walking ability without technical assistance (at least 10m). Exclusion Criteria: psychiatric disorders Severe hearing or vision loss Motor or sensory disability that may interfere with test completion Old frail group Inclusion Criteria: 65 to 90 years old 3 or more Fried's criteria of fragility walking ability without technical assistance (at least 10m). Exclusion Criteria: psychiatric disorders Severe hearing or vision loss Motor or sensory disability that may interfere with test completion