The infrapatellar fat pad plays a biomechanical role in the knee joint. After knee injury or surgery, its dynamics decrease because of an inflammatory response. Physical therapy might be one of the valuable treatments for the recovery of knee joint mobility. This study aimed to evaluate the immediate effect of physical therapy on the dynamics of the infrapatellar fat pad in healthy participants using ultrasonography. In this prospective, single-blind, randomised controlled trial, 64 healthy young participants were enrolled and randomly assigned to one of the following three interventions: manual therapy, hot pack treatment, and control. Ultrasound images of the infrapatellar fat pad were obtained before and after the intervention. The thickness change ratio of the infrapatellar fat pad was calculated to compare the changes between and within groups before and after the intervention. No significant inter-group differences were observed. The effect sizes were relatively small. Manual therapy or hot pack intervention might not have an immediate effect on infrapatellar fat pad flexibility in healthy participants. Thus, it is necessary to consider more intensive treatments to change the dynamics of the infrapatellar fat pad.