Effect of co-contraction training on intrinsic neuromodulation properties of motoneurons

• Grant number: 20/03282-0
• Support type: Scholarships abroad - Research
• Effective date (Start): August 01, 2021
• Effective date (End): July 31, 2022
• Field of knowledge: Health Sciences - Physical Education
• Principal researcher: Matheus Machado Gomes
• Grantee: Matheus Machado Gomes
• Host: Charles J. Heckman
• Home Institution: Escola de Educação Física e Esporte de Ribeirão Preto (EEFERP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil
• Research place: Northwestern University, Chicago, United States

Abstract

Among the several factors that contribute to increased muscle strength, neural adaptation seems to be the main determinant. After a few weeks of training, there is an increase in the magnitude of action potentials triggered by motoneurons (neural drive). In the past, the magnitude of the neural drive was believed to be proportional to the descending motor command from cortical pathways. Conversely, there is now considerable evidence that this assumption was incorrect and that motoneurons have intrinsic electrical properties called persistent inward currents (PICs) that amplify and prolong all motor commands. This amplification/prolongation is power, up to 3-5 fold, depending on the intensity of neuromodulatory drive from the brainstem. Studies in animal preparations have shown that PICs are highly adaptable in response to injury and disease of the CNS. This adaptability implies PICs may also adapt to exercise, but this issue has yet to be studied. Recently new techniques have been developed to identify the amplitudes of PICs in human subjects and thus the question of their adaptability can now be effectively studied. In the last decade, an interesting method for resistance training has emerged that does not require an external load called co-contraction training. The co-contraction training involves the simultaneous muscle contraction of an agonist muscle group and its respective antagonist muscle group, thereby generating mechanical resistance to each other. This alternative way to train strength seems to be very promising, with potential use in microgravity and rehabilitation settings. However, the effects of co-contraction training on the intrinsic properties of motor neurons are still unknown. The present project aims to gain more insight into the intrinsic properties of motoneuron modulation and to analyze whether PICs are modified by co-contraction training. A longitudinal study will be performed with analysis of the biceps brachii PICs and the maximal isometric elbow flexion torque before and after four weeks of co-contraction training. The PIC will be estimated by calculating the firing rate difference via paired motor unit analysis by surface high-density electromyography. We hypothesize that co-contraction training will lead to adaptations of PICs that will result in increased muscle strength. (AU)