Older persons experience an increased dependence in activities of daily living (ADLs) during and after acute illness or hospitalization in about 30% of cases. However, functional decline after unplanned hospitalization may also affect mobility, cognition, and quality of life, and it is associated with length of hospital stay, new institutionalization, readmission, progressive disability, and mortality. Because the loss of muscle strength or “acute sarcopenia” due to inactivity and bed rest may at least partially account for in-hospital functional decline, especially in frail, comorbid older patients, in-hospital exercise may prevent deconditioning and help to maintain physical function. Exercise has also been associated with cognitive improvement in older adults and may prevent delirium. A 2007 review reported inconclusive evidence to support exercise to improve functional outcomes for acutely hospitalized older adults, (1) but suggested that multidisciplinary interventions that include exercise may increase the percentage of patients discharged to home and reduce the length and cost of hospital stay. As new research was available, Peter Hartley and other authors performed an update of that review. (2) A search was carried out up to May 2021 on medical databases for studies that compared exercise programs to usual care (with or without a sham intervention) for older persons undergoing unplanned hospitalization. The authors included 24 studies (13 from Europe, 6 from Oceania, and 5 from America), with 7,511 participants (58% women), with average ages ranging across studies from 73 to 88 years. Participants were admitted to hospitals with a wide range of illnesses or medical conditions. The type and amount of exercise also varied: 9 studies investigated rehabilitation-related activities, 6 structured exercises without progressive strength training, and 9 included progressive resistance training. No studies measured whether the participants rated the exercise intervention as successful. The quality of evidence was generally low or very low for most of the included outcomes. The authors concluded that exercise may make little difference to independence in activities of daily living or quality of life, while the effects of exercise on functional mobility, the incidence of delirium, and medical deterioration are uncertain. On the other hand, because there is moderate-certainty evidence that in-hospital exercise interventions do not increase falls during hospitalization, the risk of falls should be no barrier to their implementation. Lacking higher certainty evidence, the authors recommended that clinicians rely on their evaluation to tailor exercise interventions to patients' needs and preferences. Further research providing better quality evidence will be highly relevant to drive decision-making regarding the organization of hospital care for older adults.