ORIGINAL CONTRIBUTIONS How Does Bariatric Surgery Affect Fall Risk Factors? Florêncio Diniz-Sousa 1 & Lucas Veras 1 & Giorjines Boppre 1 & Vítor Devezas 2 & Hugo Santos-Sousa 2 & John Preto 2 & Leandro Machado 3,4 & João P. Vilas-Boas 3,4 & José Oliveira 1 & Hélder Fonseca 1 Received: 14 January 2021 /Revised: 26 March 2021 /Accepted: 26 March 2021 # The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021 Abstract Purpose This study aimed to assess bariatric surgery (BS) effect on fall risk factors. Materials and methods Fifteen patients undergoing BS (intervention group, IG) and 10 non-surgical obese patients (control group, CG) were recruited. IG was assessed at pre-surgery and 6 months after BS, while CG was assessed at baseline and reassessed after 6 months. At both time-points, anthropometry, lower limbs muscle strength (isokinetic dynamometer), balance in bipedal stance (force platform), daily physical activity (accelerometry), and health-related quality of life (SF-36 questionnaire) were assessed. Results At baseline, there were no differences between CG and IG for all parameters analyzed. Compared to CG, 6 months post- BS, the IG decreased weight, body mass index, waist and hip circumference. Balance showed limited improvements, with gains observed only on antero-posterior and total center of pressure velocity. Muscle strength displayed a divergent evolution 6 months after BS, with a decrease in absolute strength but an increase in relative strength. Although BS did not induce significant changes in time spent in different physical activity intensities, it decreased time in sedentary behavior and increased number of daily steps. Post-BS patients reported substantial improvements in quality-of-life, especially in physical function. Conclusion Patients seem to overestimate their actual physical fitness improvements attained after BS, which combined with increases in physical activity, might increase the likelihood of engaging in risky daily tasks to what they are physically not prepared to, consequently increasing fall risk. Keywords Weight loss surgery . Fall risk factors . Postural control . Muscle strength . Physical activity . Perceived physical function Introduction Severe obesity is one of the leading health problems due to its increasing prevalence and associated comorbidities [1]. Bariatric surgery (BS) is the most effective treatment for severe obesity [2], but it is also associated with some draw- backs such as increased fracture risk [3]. Although the causes are poorly understood, this might be attributed, at least par- tially, to the increased risk of fall injury that occurs after BS [4]. These findings are puzzling because it is known that obe- sity is a major risk factor for falls [5] and, therefore, weight loss should, theoretically, reduce this risk. This apparent paradox suggests that there might be other risk factors for falls that could be influenced by BS. Although bariatric patients seem to report physical function improvements after surgery [6], it is still un- clear what are the real changes in key physical compo- nents related to fall risk, such as balance and muscle strength [7]. Moreover, after surgery, patients are typi- cally encouraged to increase their physical activity levels [8], which may also contribute to increase fall risk [9], especially if they misjudge their real physical function [10]. The impact of BS on these fall risk fac- tors, however, is poorly understood. * Florêncio Diniz-Sousa joseflorenciosousa@gmail.com 1 Research Centre in Physical Activity, Health and Leisure (CIAFEL), Faculty of Sport, University of Porto, Rua Dr. Plácido Costa, 91, 4200-450 Porto, Portugal 2 General Surgery Department, São João Medical Center, Porto, Portugal 3 Centre of Research, Education, Innovation and Intervention in Sport (CIFI2D), Faculty of Sport, University of Porto, Porto, Portugal 4 Biomechanics Laboratory (LABIOMEP-UP), University of Porto, Porto, Portugal https://doi.org/10.1007/s11695-021-05400-2 / Published online: 2 April 2021 Obesity Surgery (2021) 31:3506–3513