Background <p>Bariatric surgery is a recognized treatment option for severe obesity, and its effectiveness in reducing weight and controlling obesity-related conditions has been demonstrated. However, it can also lead to decreased skeletal muscle mass and strength, increasing the risk of sarcopenia after surgery. This randomized clinical trial studied the effects of a 16-week exercise program on sarcopenia in bariatric surgery patients.</p> Methods <p>Thirty-seven surgery candidates participated in the EXPOBAR (EXercise POst BARiatric) program and were randomized into experimental or control groups. The intervention lasted 16&#xa0;weeks, starting 1&#xa0;month after surgery, and included a circuit training with aerobic and resistance exercise intervention. The outcomes included physical fitness parameters (anthropometry, body composition, and physical performance) and were assessed at four time points. All participants underwent gastric bypass surgery (RYGB).</p> Results <p>The EXPOBAR trial revealed significant and meaningful effects of the exercise intervention on anthropometric indices, such as weight (<i>p</i> = 0.039) and waist circumference (<i>p</i> = 0.010). The most substantial improvements were observed in physical function and strength metrics (<i>p</i> = 0.005 and <i>p</i> &lt; 0.001, respectively), along with a reduction in fat mass (<i>p</i> = 0.006), indicating the intervention’s effectiveness on sarcopenia parameters and in enhancing both physical fitness and body composition.</p> Discussion <p>Current findings indicate that following an initial decrease due to bariatric surgery, exercise training significantly improves functional physical capacity and strength. The exercise program in this study effectively reversed the surgery-induced loss in function and strength, reducing the number of patients at risk of sarcopenia. Physical and functional capacity are crucial noninvasive indicators for diagnosing muscle quality and sarcopenia.</p> Conclusion <p>Long-term management of sarcopenia and sarcopenic obesity in bariatric surgery patients requires frequent monitoring of body composition and muscle function. This approach is essential for tracking progress and optimizing treatment strategies over time. This study highlights the importance of integrating structured exercise programs into after bariatric surgery care to mitigate the risk of sarcopenia.</p> <p><b>Trial Registration:</b> The trial was registered at Clinicaltrials.gov (NCT05289219).</p>