[en] BACKGROUNDS: The aim of this study was to assess the relationship between the level of ambulatory physical activity, measured by physical activity tracker, and the clinical components of physical frailty, among nursing home residents. METHODS: We proceeded in 3 steps: (1) Validation of the physical activity tracker (i.e. the Pebble): 24 volunteer adults walked on a treadmill. The number of steps recorded by the Pebble worn by the subjects was compared with the number of steps counted by the investigators, by means of the Intra-class correlation coefficients (ICC). (2) Measurement of ambulatory physical activity, using the Pebble trackers, over a 7-day period. (3) Relationship between the results obtained with the Pebble trackers (step 2) and subjects' clinical characteristics, linked to physical frailty. RESULTS: ICC data, showed that the reliability of the Pebble was better when it was worn at the foot level (ICC ranged from 0.60 to 0.93 depending on the tested speed). Gait speed is also an important determinant of the reliability, which is better for low gait speed. On average, the 27 nursing home residents included in the second step of this study walked 1678.4+/-1621 (median=1300) steps per day. Most physical components of frailty measured in this study were significantly different between subjects who walked less than 1300 steps per day and those who were more active. CONCLUSION: This study showed that nursing home residents have a poor ambulatory physical activity, assessed using a physical activity tracker, which is associated with poorer physical performances and higher disability.