Copyright © 2017 The Academy of Geriatric Physical Therapy, APTA. Unauthorized reproduction of this article is prohibited. Journal of GERIATRIC Physical Therapy 1 Research Report INTRODUCTION Frailty is a common and important geriatric syndrome, distinct from any single chronic disease, 1 and it is char- acterized by an age-associated decline in physiological reserve and function across multiple systems, 2 particularly the immune, endocrine, musculoskeletal, and nervous sys- tems. 3 This altered network leads to a state of high vulner- ability to adverse health outcomes, such as mobility issues, falls, hospitalization, and mortality. 4,5 There is no consen- sus on a universal definition of frailty or a single tool to be used in assessing the syndrome. 6 The physiological changes that result in frailty are complex, and it has thus far been extremely difficult to characterize them because of the fre- quent coexistence of acute and chronic illnesses. 4 The causes of this loss in physiological reserve and func- tion are likely multifactorial. 7 Malnutrition and immobility are considered to be the key to the development of frailty. Slow walking speed is the most reliable variable for screen- ing and predicting frailty, and it is a function of fear of fall- ing and neurological and musculoskeletal deficits. 6 Limited mobility has been associated with lower PALs, especially 3rd, 7th, 12th, 13th, and 14th days after the baseline collec- tion and analyzed by mass spectrometry. Results and Discussion: The older adults who were frail pre- sented significantly lower PAEE (1453.7 [1561.9] vs 3336.1 [1829.3] kj/d, P < .01), PAL (1.4 [0.3] vs 1.9 [0.6], P = .04), and TEE (7919.0 [2151.9] vs 10442.4 [2148.0] kj/d, P < .01) than the older adults who were nonfrail. There was no difference in their RMRs (5673.3 [1569.2] vs 6062.0 [1891.7] kj/d, P = .57). Frailty has been associated with a smaller lean body mass and with a disease-related hyper- metabolic state, which might explain the lack of difference in the RMR. The PAL of the older adults who were frail was below the recommended level for older adults and deter- mined a lower PAEE and TEE when compared with older adults who were not frail. Conclusion: This study showed that low energy expenditure in physical activity is a main component of frailty. The PAL of the older adults who were frail was far below the recommended level for older adults. Key words: doubly labeled water, energy expenditure, frailty, older adults (J Geriatr Phys Ther 2017;00:1-7.) ABSTRACT Background and Purpose: Frailty is a common and important geriatric syndrome, distinct from any single chronic disease, and an independent predictor of mortality. It is characterized by age-associated decline in physiological reserve and func- tion across multiple systems, culminating in a vicious cycle of altered energy expenditure. The total energy expenditure (TEE) of an individual includes the resting metabolic rate (RMR), the thermic effect of feeding, and the energy expendi- ture in physical activity (PAEE). The investigation of the energy expenditure of older adults who are frail is essential for better understanding the syndrome. Therefore, we compared the RMR, the PAEE, the physical activity level (PAL), and the TEE of older adults who were frail with those who were not frail. Methods: A cross-sectional study was conducted with 26 community-dwelling older adults (66-86 years of age). Older adults in the frail and nonfrail groups were matched for age and gender, and the matched pairs were randomly selected to continue the study. The RMR was measured by indirect calorimetry. The TEE was obtained by the multipoint, doubly labeled water method. After collecting a baseline urine sam- ple, each participant received an oral dose of doubly labeled water composed of deuterium oxide and oxygen-18 ( 2 H 2 18 O). Subsequently, urine samples were collected on the 1st, 2nd, Energy Expenditure in Older Adults Who Are Frail: A Doubly Labeled Water Study Alessandra de Carvalho Bastone, PT, PhD 1 ; Eduardo Ferriolli, MD, PhD 2 ; Karina Pfrimer , N, PhD 2 ; Bruno de Souza Moreira, PT, PhD 3 ; Juliano Bergamaschine Mata Diz, PT, MS 3 ; João Marcos Domingues Dias, PT, PhD 3 ; Rosângela Corrêa Dias, PT, PhD 3 1 Department of Physical Therapy—Federal University of Jequitinhonha and Mucuri Valleys, Diamantina, Minas Gerais, Brazil. 2 Division of General Internal and Geriatric Medicine, School of Medicine—Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil. 3 Postgraduate Program in Rehabilitation Sciences—Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil. This work received funding from the Brazilian National Council of Technological and Scientific Development—CNPQ. The authors declare no conflicts of interest. Address correspondence to: Alessandra de Carvalho Bastone, PT, PhD, Department of Physical Therapy— Federal University of Jequitinhonha and Mucuri Valleys, Campus JK, Rodovia MGT 367, Km 583, N 5000, Bairro Alto da Jacuba, Diamantina, MG, Brazil-CEP 39100-000 (ale.bastone@gmail.com). Robert Wellmon was the Decision Editor. Copyright © 2017 Academy of Geriatric Physical Therapy, APTA. DOI: 10.1519/JPT.0000000000000138