A randomized crossover clinical trial evaluated postexertional symptoms in patients with post-COVID condition (PCC) compared to healthy controls. Thirty-one patients with PCC and 31 healthy controls participated. Participants underwent three exercise trials (HIIT, MICT, and ST) and reported symptoms before, immediately after, and 48 hours post-exercise. Patients with PCC reported more symptoms than controls at all time points, but no significant difference in fatigue worsening was observed across exercise types. However, PCC patients experienced greater muscle pain after HIIT and concentration difficulties after MICT compared to controls. PCC patients had lower aerobic capacity and less muscle strength than controls, with 62% showing myopathic signs. Despite these findings, PCC patients generally tolerated exercise with preserved cardiovascular function. The study suggests that cautious exercise rehabilitation should be recommended to prevent further deconditioning in PCC patients. The results indicate that while exercise does not significantly worsen symptoms in PCC patients, they have lower aerobic capacity and muscle strength, and some show signs of myopathy and orthostatic intolerance. The findings support the need for careful, individualized exercise programs for PCC patients.A randomized crossover clinical trial evaluated postexertional symptoms in patients with post-COVID condition (PCC) compared to healthy controls. Thirty-one patients with PCC and 31 healthy controls participated. Participants underwent three exercise trials (HIIT, MICT, and ST) and reported symptoms before, immediately after, and 48 hours post-exercise. Patients with PCC reported more symptoms than controls at all time points, but no significant difference in fatigue worsening was observed across exercise types. However, PCC patients experienced greater muscle pain after HIIT and concentration difficulties after MICT compared to controls. PCC patients had lower aerobic capacity and less muscle strength than controls, with 62% showing myopathic signs. Despite these findings, PCC patients generally tolerated exercise with preserved cardiovascular function. The study suggests that cautious exercise rehabilitation should be recommended to prevent further deconditioning in PCC patients. The results indicate that while exercise does not significantly worsen symptoms in PCC patients, they have lower aerobic capacity and muscle strength, and some show signs of myopathy and orthostatic intolerance. The findings support the need for careful, individualized exercise programs for PCC patients.