Muscle-tendon unit morphological and mechanical adaptations to eccentric and concentric training

• Applicant: Professor Dr. Daniel Hahn
• Subject Area: Orthopaedics, Traumatology, Reconstructive Surgery
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 565338450

Muscles are the motors of life. With their strength, muscles enable movement, but muscles can also act as brakes, dampers, springs, or structural ties, thereby ensuring not just mobility but also stability and posture. Furthermore, muscles can adapt and change acutely and chronically through exercise and training, but also due to injury, illness, or ageing. It is therefore very important to understand muscle function and their changes. This can help to effectively design preventative and rehabilitative training strategies to maintain mobility over the lifetime or to restore muscle function after injury or illness. Strength training to improve, to maintain or to regain muscle strength can be carried out in different ways: When muscles generate force while shortening, this is called concentric training; when muscles generate force but are stretched by an external force exceeding the muscle force, this is called eccentric training. Eccentric training has received a great deal of attention in recent years. This is particularly true regarding its use in preventative, rehabilitative and clinical contexts, e.g. to prevent muscle injuries, to improve strength and mobility in old age and to treat neuromuscular diseases. However, due to methodological shortcomings, it remains unclear whether eccentric training actually causes specific adaptations of the muscle-tendon unit. Therefore, the overarching goal of this research is to use improved methodology to investigate whether eccentric muscle training leads to specific mechanical and morphological adaptations of the muscle-tendon unit compared with concentric muscle training. For this purpose, a comprehensive training study will be conducted in a randomized crossover design including a control group. Compared to previous research, a new matching strategy will be used that allows the training load of eccentric and concentric training to be controlled and monitored over the entire training period and thus allows conclusions to be drawn about the effect of the contraction type (eccentric versus concentric). Furthermore, in contrast to previous studies, muscle architecture and muscle morphology will be comprehensively determined using 3D ultrasound. For the first time, this allows to determine mechanical and morphological properties of aponeuroses (fascia), which play an important role in efficient locomotion and whose changes can represent a decisive stimulus for growth and remodeling of muscle. In conclusion, this research project contributes to a better understanding of specific adaptations of the muscle-tendon unit to training. This will form the basis for effective training strategies in prevention and rehabilitation.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Brent James Raiteri, Ph.D.