Contractile, elastic, and neural mechanisms of muscular performance enhancement during stretch-shortening cycles.

• Applicants: Professor Dr. Daniel Hahn; Dr. Florian Paternoster; Professor Dr. Wolfgang Seiberl; Professor Dr. Tobias Siebert
• Subject Area: Orthopaedics, Traumatology, Reconstructive Surgery ; Anatomy and Physiology ; Systematics and Morphology (Zoology)
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 354863464

The stretch-shortening cycle (SSC) refers to the contraction condition when an active muscle stretch is immediately followed by active muscle shortening. This combination of eccentric and concentric contractions is the most important contraction condition during human locomotion including patterns such as walking, running or jumping. Two special features characterize SSCs: First, during the concentric push-off phase of a SSC, force, work, and power production are increased by up to 50% compared with a purely concentric contraction without preceding eccentric stretch. Second, this increase in performance during SSCs is accompanied by an increased efficiency. During a first DGF funding period, we identified several contractile, elastic and neuronal mechanisms that contribute to the performance enhancement during SSCs.In this follow-up funding period, one key aspect is the identification of further basic mechanisms underpinning the performance enhancement during SSCs. Additionally, our research will focus on SSC conditions close to everyday life scenarios. The joint project uses a holistic approach with closely intertwined experiments on different structural levels of muscle. These experiments will investigate how neural muscle activation and different muscle fiber types affect the performance enhancement during SSCs and how the performance enhancement during SSCs is driven by passive-elastic elements of the muscle-tendon unit. From an applied perspective and according to typically cyclic locomotion, repetitive SSCs and complex multi-joint leg extensions as they occur e.g. during walking or running will be investigated. Again, the repetitive SSCs will be investigate on different structural levels of muscle.Performing experiments on the different structural levels of muscle from single fibers to complex multi-joint leg extensions comes with several advantages: Experiments on single muscle fibers allow conclusions to be drawn about the contractile and passive structures of the muscle cell. The in vivo experiments with humans provide information on how the interaction of muscles and tendons, and how neuronal activation affect the performance enhancement during SSCs. Finally, the investigation of multi-joint leg extensions allows an assessment of the biomechanics and muscle coordination of contraction conditions similar to those of locomotion. In combination with the findings of the first funding period, this research project contributes to a better understanding of the SSC. This is not only important for a fundamental understanding of human locomotion, but can also have applications in the fields of medical technology, robotics and prosthetics, as well as for the development of efficient humanoid drives.

• DFG Programme: Research Grants