There are few studies that already have validated specific raw accelerometer cut-points for people over 65 years old.

The purpose of the present study is to validate raw accelerometer cut points for general people over 65 years old and specific raw accelerometer cut points based on the functional status of older adults over 65 years old.

The study will be carried out with an observational approach. Participants will be divided into 4 groups. First of them will be made grouping all subjects and the rest divided according to their functional status. They will perform different-intensity physical activities while wearing accelerometers attached to their body and wearing a portable gas analyser too. Their intensity will be assessed based on their own Rest Metabolic Rate (RMR). Energy expenditure and accelerations will be matched and, based on that, sedentary behaviour, light physical activity and moderate-to-vigorous physical activity cut-points will be derived.

Knowledge on health implications of sedentary time and physical activity has been substantially improved in the last decades with accelerometer-based estimations. The popularity of these devices is partially explained by the capacity of objectively recording physical behaviors (e.g., sleep, sedentary time, physical activity…) during the whole day. The so-called "cut-point" approach is behind most of the research on physical activity with accelerometers. Cut-points provide metrics that are easy to understand, to translate to the public and to replicate by researchers in different settings. Usually, the minimum requirement is to use cut-points adapted to the age-group of the population of interest.

Under this paradigm, cut-points have been developed in all age-groups and with a variate set to data collection and processing protocols. However, some scenarios lack of available cut-points to implement, being older adults (> 65 years) the population with less alternatives of cut-points to use. In this sense, studies with older adults choose cut-points developed in younger adults to classify physical activity intensities. Biomechanical and physiological differences between adults and older adults advise against using this strategy. Therefore, relative energy expenditure and functional status should be considered for future cut-points design. Moreover, must be also awarded that hardly any previous cut-points validation protocols have been performed in a free-living setting. For this reason, more studies following these designs seems necessary to improve cut-points population's validity. Missing all mentioned factors could lead to physical activity and sedentary behavior patterns misclassification in this population.

Inclusion Criteria:

• 65 years and older
• Non-institutionalized
• Physical function assessment (SPPB>3)

Exclusion Criteria:

• Have started an exercise program.
• Mini-Mental Score < 18.
• Presenting any physical activity contraindication.

People over 65 years old will be enrolled in the study. They will be recruited from the Frailty Consultation in the Virgen del Valle Hospital from Toledo (Spain).