Tehran University of Medical Sciences Journal of Modern Rehabilitation 2538-385X 18 1 2024 01 01 127 132 Ardalan Parsa Department of Physical Therapy, Iran University of Medical Science, School of Rehabilitation, Tehran, Iran Zahra Poursaleh Begi Department of Physical Therapy, Iran University of Medical Science, School of Rehabilitation, Tehran, Iran Ali Amiri Department of Physical Therapy, Iran University of Medical Science, School of Rehabilitation, Tehran, Iran Nastaran Bahadorani Department of Physical Therapy, Tehran University of Medical Science, School of Rehabilitation, Tehran, Iran Amirhossein Shamsi Department of Physical Therapy, Tehran University of Medical Science, School of Rehabilitation, Tehran, Iran 2022 07 07 2022 09 05 Introduction: Hamstring injuries are one of the most common tendon injuries, especially in sports that require running and jumping. A comprehensive training program can help athletes to prevent this injury. Among suggested exercises, the Nordic eccentric training can reduce the injury rate by up to 50%; however, it is a high-load exercise that cannot be prescribed in the first stages of rehabilitation. Here, we describe a football player who used low-load resistance exercise with blood flow restriction as an alternative method to strengthen their hamstring after nine months of anterior cruciate ligament reconstruction surgery. Case Description: A 19-year-old non-professional footballer with a body mass index of 22.18 kg/cm2 was invited to participate in this study. The variables examined included strength and cross-sectional area of the hamstring muscles (mean and maximum strength) and the cross-sectional area of the hamstring tendons at their origin. The treatment program included a seated hamstring curl with a load of 30% 1 RM with blood flow restriction for four weeks (thrice a week). Results: The hamstring muscle strength improved by 6.54%, and the cross-sectional area of the muscles and tendons changed as follows: Semimembranosus (tendon=0.07%, muscle=2.57%), semitendinosus (tendon=0.00%, muscle=-4.04%), and biceps-femoris (tendon=5.5%, muscle=4.34%). Conclusion: Low load resistance training with blood flow restriction in this athlete improved the strength and cross-sectional area of the hamstring muscles as well as the cross-sectional area of the tendons. The changes observed in tendon, and muscle cross-sectional areas were more prominent for biceps-femoris. This case showed that a training program with blood flow restriction may be a good alternative for people who cannot tolerate high-load exercises in the early stages of their rehabilitation. Doing more extensive studies with more cases and a control group in the future can help our knowledge in giving the best exercise prescription to our patients. https://jmr.tums.ac.ir/index.php/jmr/article/view/702