Eccentric training found to improve flexibility as effectively as stretching

Improving flexibility has traditionally required stretching, while increasing muscle strength and size has required strength training. Researchers have now demonstrated that both goals can be achieved simultaneously through "eccentric-only training," a form of resistance exercise in which muscles produce force while being stretched for an extended period. The training approach was proposed and validated through an intervention study conducted by a research team including Lecturer Raki Kawama at the Faculty of Health and Sports Science, Waseda University (at the time of research, Specially Appointed Assistant Professor at the Organization for Research Initiatives and Development, Doshisha University), Professor Masatoshi Nakamura at the Faculty of Rehabilitation, Nishikyushu University, and Professor Taku Wakahara at the Faculty of Health and Sports Science, Doshisha University. The study was published in the Journal of Applied Physiology.

Static stretching is widely used in sports and rehabilitation settings to improve muscle flexibility. The research group previously showed that "eccentric-only training," in which muscles produce force while being lengthened under prolonged stretch, can permanently reduce stiffness in specific hamstring muscles. However, whether this training method improves flexibility as effectively as conventional static stretching had not been determined.

The researchers conducted a 10-week intervention involving 11 healthy young men, with training performed three times per week. One leg of each participant was assigned to eccentric-only training (ECC), in which the muscles produced force while being lengthened under prolonged stretch, whereas the contralateral leg underwent conventional static stretching with the knee extended. The time spent on each intervention was identical. To evaluate the effects of the two approaches, the team measured hamstring stiffness using ultrasound shear wave elastography, muscle volume using MRI, and knee-flexor strength and joint flexibility using a dynamometer before and after the intervention.

As a result, in both strength training and static stretching, the stiffness of the long head of the biceps femoris and the semimembranosus among the hamstrings permanently decreased. On the other hand, no significant change was observed in the stiffness of the semitendinosus. Joint flexibility increased to a similar extent under both conditions.

Furthermore, in the leg subjected to ECC, maximal muscle strength increased, and the muscle sizes of the long head of the biceps femoris, semitendinosus, and semimembranosus also increased significantly. In contrast, with static stretching, although changes were seen in the size of some muscles, no increase in maximal muscle strength was observed.

The researchers say this is the first intervention study to show that eccentric-only training (ECC) is as effective as static stretching for improving muscle flexibility. Their results indicate that regularly performing ECC over an extended period can reduce stiffness in specific muscles to a similar degree as static stretching, while delivering significantly greater increases in muscle size and strength.

Journal Information
Publication: Journal of Applied Physiology
Title: Similar adaptation in shear moduli of the biarticular hamstring muscles after eccentric-only training and static stretching
DOI: 10.1152/japplphysiol.00026.2026