Researchers from The University of Queensland and the University of Southern Queensland, working with Stanford University, published new findings on Apr. 16 that explain why eccentric training, such as the Nordic hamstring exercise, can help prevent common hamstring injuries in sports.
Hamstring injuries are frequent among athletes who sprint or accelerate quickly. These injuries often cause significant time away from competition and represent about 10 percent of all injuries in field-based sports. While exercises like the Nordic hamstring exercise have been shown to reduce injury risk, the reason for their effectiveness has not been fully understood.
The study involved nine weeks of supervised Nordic hamstring exercise training for participants. Researchers measured changes in muscle strength and used ultrasound imaging to observe muscle fiber behavior. They also estimated sarcomere lengths by combining fascicle length measurements with previous data on serial sarcomere numbers.
After the training period, participants showed a roughly 40 percent increase in eccentric knee flexor strength and could perform the exercise through a greater range of motion. Muscle fibers reached about 25 percent longer lengths during movement after training, but individual sarcomere lengths did not change. According to Dr. Max Andrews, first author of the study and postdoctoral fellow at The University of Queensland: "Previous research has shown that exercises such as the Nordic hamstring exercise are very effective at reducing hamstring injury risk." Senior author Dr. Patricio Pincheira from the University of Southern Queensland said: "Following training, the muscle fibers can stretch to longer lengths during the exercise without overstretching the sarcomeres... This may be one reason why eccentric training is effective at reducing hamstring injury risk." He added: "Our findings suggest that the muscle adapts in a way that allows it to generate force at longer lengths, which may help the hamstrings tolerate the large mechanical demands placed on them during dynamic movements."
These results indicate that structural adaptation within muscles—specifically adding more sarcomeres end-to-end—may allow athletes' muscles to handle greater stretching without damage during activities like sprinting.
The researchers believe this understanding could improve how coaches and clinicians design programs aimed at preventing persistent athletic injuries.
